DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Part 571
Docket No. NHTSA-00-8011
RIN 2127-AI54
Federal Motor Vehicle Safety Standards; Tires
AGENCY: National Highway Traffic Safety Administration (NHTSA), Department of Transportation.
ACTION: Notice of proposed rulemaking (NPRM).
SUMMARY: The Transportation Recall Enhancement, Accountability, and Documentation Act of 2000 mandates a rulemaking proceeding to revise and update our safety performance requirements for tires. In response, this document proposes to establish new and more stringent tire performance requirements in a new Federal motor vehicle safety standard that would apply to all new tires for use on vehicles with a gross vehicle weight rating of 10,000 pounds or less. The agency recently proposed to establish a new tire standard, Standard No. 139, in a December 2001 NPRM on tire safety information. Today's document proposes to include the new tire performance requirements in that standard.
This document seeks comments on the proposed new standard, including its applicability and test procedures, modifications to related existing standards, and lead time provided for manufacturers to achieve compliance. It also seeks comments on the possible future specification of shearography analysis, a technique which evaluates the condition of a tire using laser technology. Finally, it seeks comments on NHTSA's research plans.
DATES: You should submit your comments early enough to ensure that Docket Management receives them not later than [INSERT DATE 6O DAYS AFTER DATE OF PUBLICATION IN THE FEDERAL REGISTER].
ADDRESSES: You may submit your comments in writing to: Docket Management, Room PL-401, 400 Seventh Street, SW., Washington, DC, 20590. Alternatively, you may submit your comments electronically by logging onto the Docket Management System website at http://dms.dot.gov. Click on "Help & Information" or "Help/Info" to view instructions for filing your comments electronically. Regardless of how you submit your comments, you should mention the docket number of this document.
FOR FURTHER INFORMATION CONTACT:
For technical and policy issues: Mr. George Soodoo or Mr. Joseph Scott, Office of Crash Avoidance Standards, National Highway Traffic Safety Administration, 400 Seventh Street, SW, Washington, DC 20590. Telephone: (202) 366-2720. Fax: (202) 366-4329.
For legal issues: Nancy Bell, Attorney Advisor, Office of the Chief Counsel, NCC-20, National Highway Traffic Safety Administration, 400 Seventh Street, SW, Washington, DC 20590. Telephone: (202) 366-2992. Fax: (202) 366-3820.
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Table of Contents
I. Executive Summary and Overview
Section 10 of the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act mandates that the agency issue a final rule to revise and update its tire performance standards. However, the Act gives the agency substantial discretion over the substance of the final rule. The Act does not specify what revisions or updatings should be made. For example, it does not specify which particular existing tests should be improved or how much they should be improved. Likewise, it does not specify which particular new tests should be added or how stringent they should be. However, the legislative history does contain specific references to some tests like aging tests.
In response to section 10, the agency comprehensively examined possible ways of revising and updating its tire standards. In doing so, it placed particular emphasis on improving the ability of tires to withstand the effects of factors mentioned during the consideration and enactment of the TREAD Act such as tire heat build up, low inflation, and aging. The agency has examined the value of modifying the existing tests in its tire standards. In addition, it has examined the value of adopting several new tests.
As a result of these efforts, the agency has identified an array of amendments for revising and updating its tire standards and thereby improving tire performance. Some would upgrade existing tests, while the others would add new ones.
The agency recently proposed to establish a new tire standard, Standard No. 139, in a December 2001 NPRM on tire safety information (Docket No. NHTSA-01-11157, 66 FR 65536, December 19, 2001). Today's document proposes to include the new tire performance requirements in that standard. The standard would apply to light vehicle tires. As used in the December 2001 proposal, "light vehicles" are vehicles (except motorcycles) with a gross vehicle weight rating (GVWR) of 10,000 pounds or less.
Under today's proposal, the new standard would contain requirements and test procedures addressing the following aspects of tire performance: Tire Dimension, High Speed, Endurance, Road Hazard Impact, Bead Unseating, Low Inflation Pressure, and Aging Effects. (1)
The proposed High Speed and Endurance tests would replace the current High Speed and Endurance tests in FMVSS No. 109, New Pneumatic Tires - Passenger Cars, 49 CFR 571.109, with a more stringent combination of testing parameters (ambient temperature, load, inflation pressure, speed, and duration.) Most significantly, the proposed High Speed test specifies test speeds (140, 150 and 160 km/h (88, 94, and 100 mph)) that are substantially higher than those currently specified in FMVSS No. 109 (120, 128, 136 km/h (75, 80, 85 mph)). Likewise, the proposed Endurance Test specifies a test speed 50 percent faster (120 km/h (75 mph)) than that currently specified in FMVSS No. 109 (80km/h (50 mph)), as well as a duration 6 hours longer (40 hours total) than that currently specified in FMVSS No. 109 (34 hours total). At the specified test speed (120 km/h), the Proposed Endurance Test distance (4800 km) is almost double the distance accumulated than under the current Endurance Test (2720 km at 80 km/h). These new testing parameters are based on NHTSA's activities undertaken in response to the TREAD Act, including extensive agency testing, data gathering and analyses as well as agency review of other existing international, industry and National standards and proposals, and submissions by the public.
The proposed Road Hazard Impact Test and the Bead Unseating Test are modeled on SAE Recommended Practice J1981, Road Hazard Impact Test for Wheel and Tire Assemblies (Passenger Car, Light Truck, and Multipurpose Vehicles), and the Toyota Air Loss Test, respectively. These new tests would replace the Strength and Bead Unseating Resistance tests in the current FMVSS No. 109 with tests that are more dynamic as opposed to quasi-static.
In addition to the tests cited above, the proposed standard contains tests for two new aspects of performance: Low Inflation Pressure Performance and Aging Effects. By creating tests for these aspects of performance, the agency is attempting to address concerns raised by members of Congress in hearings that preceded the enactment of the TREAD Act that NHTSA's current test requirements do not evaluate how well tires perform when significantly underinflated or after being subjected to environmental variables, such as heat, which accelerate aging. In particular, underinflation and heat were factors highlighted as contributing to failure of the Firestone ATX and Wilderness tires in the TREAD hearings, and in the agency's Firestone investigation (NHTSA Office of Defects Investigation (ODI) investigation number EA00-023).
To test Low Inflation Pressure Performance, the agency is proposing two alternative tests based on agency testing and data analyses. Both tests utilize tires significantly under-inflated, for instance 20 psi for P-metric tires (the low inflation pressure threshold requirement for warning lamp activation in the proposed Tire Pressure Monitoring System (TPMS) standard, Docket No. NHTSA-00-8572 (66 FR 38982, July 26, 2001)), as the "inflation pressure" testing parameter for standard load P-metric tires. To test for resistance to Aging Effects, the agency proposes three alternative tests that would evaluate a tire's long term durability through methods different than and/or beyond those required by both the current and the proposed Endurance Test parameters. The three tests use peel strength testing, long-term durability endurance requirements, and oven aging, respectively. The agency solicits comments on which of the two proposed tests for addressing Low Inflation Pressure Performance, and which of the three tests proposed for addressing Aging Effects, should be chosen for the new standard.
In addition to proposing test procedures for the new standard, the agency also discusses in this document its ongoing and future research plans on tire safety, and seeks comments on the future use of shearography analysis (a method of analysis using laser technology) for evaluating the condition of tires subjected to the proposed testing procedures and the plans for revising the Uniform Tire Quality Grading Temperature Grading Requirement testing speeds so that they are consistent with the test speeds in the proposed High Speed tests.
Finally, the agency discusses revising FMVSS Nos. 110, Tire selection and rims, for passenger cars, 49 CFR 571.110, and 120, Tire selection and rims for motor vehicles other than passenger cars, 49 CFR 571.120, to reflect the applicability of the proposed light vehicle tire standard to vehicles up to 10,000 pounds GVWR, and revising FMVSS Nos. 117, Retreaded pneumatic tires, 49 CFR 571.117, and 129, New non-pneumatic tires for passenger cars, 49 CFR 571.129, to replace the performance tests which reference or mirror those in FMVSS No. 109 with those specified in the proposed new light vehicle tire standard.
Wishing to adopt only those amendments that contribute to improved safety, and mindful of the principles for regulatory decisionmaking set forth in Executive Order 12866, Regulatory Planning and Review, NHTSA has examined the benefits and costs of these amendments. Its efforts to do so, however, have been limited by several factors. Two factors stand out. One is the limited time allowed by the schedule specified in the TREAD Act for completing this rulemaking. That has limited the amount and variety of information that the agency could obtain and testing that the agency could conduct to examine the effects of different versions of the amendments under consideration. The other is the difficulty inherent in crash avoidance rulemakings, stemming from the multiplicity of the factors contributing to the occurrence of any crash and the difficulty of ascertaining the relative contribution of each factor, in linking specific improvements in safety requirements with specific reductions in crashes and resulting deaths and injuries. Together, these limitations have made it difficult to assess and compare the benefits and costs of this rulemaking.
At this time, the agency believes that improving tires will be beneficial in reducing tire failures and crashes resulting from tire failures. However, we do not have a good estimate of the extent to which the improvements will improve safety. We have made an estimate of the target population - 373 fatalities and 9,247 injuries in the target population. If the improvements needed to pass the high-speed and endurance tests (estimated to be 22 percent) related directly to an improvement in safety, the total potential improvement would be 82 lives saved (373* .22) and 2,034 injuries avoided. Since 32.8 percent of the tires currently do not pass the proposed requirements, the benefits would be 27 lives saved (373 * 0.22 * 0.328) and 667 injuries reduced.
The agency emphasizes that not all benefits could be quantified. Specifically, the agency believes that there will be other, currently non-quantifiable, benefits from the proposed Aging test and aspects of the proposal that address the overloading of vehicles. Additionally, there could be benefits from the proposed Low Inflation Pressure Performance tests and from the proposed Road Hazard and Bead Unseating tests.
The agency's estimate of the price increase to improve tires up to the performance levels required in the High Speed and Endurance tests is $3 per affected tire. Based on testing, we estimate that about one-third (32.8 percent) of all tires would need improvements to pass those two tests. If the cost for these improved tires were spread across the entire new light vehicle fleet, the average new vehicle price increase would, we estimate, be $4.09 per vehicle. The overall annual cost of these tests for new original equipment (64 million tires) and replacement tires (223 million tires) is estimated at $282 million for a total of 287 million tires sold annually and the net costs per equivalent life saved would be about $7.2 million.
We do not anticipate an increase in costs for the proposed Road Hazard Impact and Bead Unseating tests because our testing indicates that most of current production tires would pass these tests. The agency has not conducted sufficient testing of the proposed Aging tests to anticipate their potential costs. The agency believes, however, that most manufacturers already perform an aging test. Therefore, it is likely that the incremental cost of adding an aging test would be minimal.
With regard to the Low Inflation Pressure Performance tests, one alternative would provide no added costs because agency testing indicates that current production tires pass the test. Tires tested to the other alternative have a higher failure margin. Costs for this test cannot be characterized by the agency at this point.
The agency is concerned about the overall costs of this rulemaking and the net costs per equivalent life saved. While the agency believes that its proposed amendments represent a reasoned proposal that is based on best currently available information and that would improve tire safety, it is concerned about the apparent overall costs of those amendments. The agency is particularly concerned that the cost per equivalent life saved is significantly higher than that in most NHTSA vehicle safety rulemakings.
Because of the broad mandate from Congress and the uncertainty associated with the analysis of benefits and costs, the agency believes that the most appropriate course of action is for it to seek public comment on the full array of potential amendments that it has identified. As a result of this NPRM, the agency anticipates receiving cost data and other information that will enable it to refine its assessment of benefits and costs. The agency will then be in a better position to pick and choose among the proposed amendments. Its intention is to use that information to fashion a final rule consistent with the principles of Executive Order 12866.
II. Background
The Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, Pub. L. 106-414, signed into law on November 1, 2000, requires the agency to address numerous vehicle safety matters through rulemaking. Section 10 of the Act directs the Secretary of Transportation to conduct a rulemaking to revise and update the tire safety standards published at 49 CFR 571.109 and 571.119, and to complete the rulemaking, i.e., issue a final rule, by June 1, 2002. (2)
III. Existing Tire Standards - Performance Requirements
The following discussion summarizes current provisions relating to tires.
FMVSS No. 109, New pneumatic tires, 49 CFR 571.109, specifies the requirements for all tires manufactured for use on passenger cars manufactured after 1948. This standard, which was issued in 1967 under the National Traffic and Motor Vehicle Safety Act (Safety Act), specifies dimensions for tires used on passenger cars and requires that the tires meet specified strength, resistance to bead unseating, endurance, and high speed requirements, and be labeled with certain safety information. FMVSS No. 109 applies to passenger car (P-metric) tires produced for use on passenger cars, multipurpose passenger vehicles (MPV), and light trucks (sport utility vehicles (SUV), vans, minivans, and pickup trucks). The standard was adopted from the Society of Automotive Engineers (SAE) recommended practice J918c, Passenger Car Tire Performance Requirements and Test Procedures, which was first issued by the SAE in June 1965. (3) The current FMVSS No. 109 includes four performance requirements for tires:
For the purposes of testing tires to determine their compliance with these requirements, the standard specifies values for several factors, such as tire inflation pressure, the load (4) on the tire, and the rim on which a tire is mounted. The standard specifies permissible inflation pressures (or wheel sizes, in the case of bead unseating test) to facilitate compliance testing. The standard requires that each passenger car tire must have a maximum permissible inflation pressure labeled on its sidewall (S4.3). Section 4.2.1(b) lists the permissible maximum pressures: 32, 36, 40, or 60 pounds per square inch (psi) or 240, 280, 290, 300, 330, 340, 350, or 390 kiloPascals (kPa). A manufacturer's selection of a maximum pressure has the effect of determining the pressures at which its tire is tested. For each permissible maximum pressure, Table II of the standard specifies pressures at which the standard's tests must be conducted. The intent of this provision is to limit the number of possible maximum inflation pressures and thereby reduce the likelihood of having tires of the same size on the same vehicle with one maximum load value, but with different maximum permissible inflation pressures.
Closely related to FMVSS No. 109 is FMVSS No. 110, Tire selection and rims, 49 CFR 571.110. FMVSS No. 110 requires that each passenger car be equipped with tires that comply with FMVSS No. 109, that tires on the cars be capable of carrying the GVWR of that vehicle, that the rims on the car be appropriate for use with the tires, and that certain information about the car and its tires appear on a placard in the passenger car. FMVSS No. 110 also specifies rim dimension requirements and further specifies that, in the event of a sudden loss of inflation pressure at a speed of 97 km/h (60 mph), rims must retain a deflated tire until the vehicle can be stopped with a controlled braking application. FMVSS No. 110 initially became effective in April 1968.
FMVSS No. 117, Retreaded pneumatic tires, 49 CFR 571.117, establishes performance, labeling, and certification requirements for retreaded pneumatic passenger car tires. Among other things, the standard requires retreaded passenger car tires to comply with the tubeless tire resistance to bead unseating and the tire strength requirements of FMVSS No. 109. FMVSS No. 117 also specifies requirements for casings to be used for retreading, and certification and labeling requirements.
FMVSS No. 119, New pneumatic tires for vehicles other than passenger cars, 49 CFR 571.119, specifies performance and labeling requirements for new pneumatic tires designed for highway use on multipurpose passenger vehicles, trucks, buses, trailers and motorcycles manufactured after 1948, and which requires treadwear indicators in tires, and rim matching information concerning those tires. Under this standard, each tire has to meet requirements that are qualitatively similar to those in FMVSS No. 109 for passenger car tires. The high speed performance test in this standard only applies to motorcycle tires and to non-speed-restricted tires of 14.5-inch nominal rim diameter or less marked load range A, B, C, or D. In addition, FMVSS No. 119 does not contain a resistance-to-bead unseating test.
A tire under FMVSS No. 119 is generally required to meet the performance requirements when mounted on any rim listed as suitable for its size designation in the publications, current at the time of the tire's manufacture, of the tire and rim associations that are listed in the standard. Further, the tire is required to meet the dimensional requirements when mounted on any such rim of the width listed in the load-inflation tables of this standard. In addition to the permanent marking for any non-matching listed rims, each tire manufacturer is required to attach to the tire, for the information of distributors, dealers and users, a label listing the designations of rims appropriate for use with the tire.
FMVSS No. 120, Tire Selection and rims for motor vehicles other than passenger cars, 49 CFR 571.120, requires that vehicles other than passenger cars equipped with pneumatic tires be equipped with rims that are listed by the tire manufacturer as suitable for use with those tires and that rims be labeled with certain information. It also requires that these vehicles shall be equipped with tires and rims that are adequate to support the fully-loaded vehicle under contemplated operating conditions.
The primary effect of Standard No. 120 is to specify the minimum load-carrying characteristics of tires not already subject to the passenger car tire and rim selection requirements of FMVSS No. 110.
Tire selection under FMVSS No. 120 consists of two elements. With one exception, each vehicle must be equipped with tires that comply with FMVSS No. 119 and the load rating of those tires on each axle of the vehicle must together at least equal the gross axle weight rating (GAWR) for that axle. If the certification label lists more than one GAWR-tire combination for the axle, the sum of the tire's maximum load ratings must meet or exceed the GAWR that corresponds to the tire's size designation. If more than one combination is listed, but the size designation of the actual tires on the vehicle is not among those listed, then the sum of the load ratings must simply meet or exceed the lowest GAWR that does appear.
FMVSS No. 120 also contains a requirement related to the use of passenger car tires on vehicles other than passenger cars. The requirement states that when a tire that is subject to FMVSS No. 109 is installed on a multipurpose passenger vehicle, truck, bus, or trailer, the tire's load rating must be reduced by a factor of 1.10 by dividing by 1.10 before determining whether the tires on an axle are adequate for the GAWR. This 10 percent de-rating of P-metric tires provides a greater load reserve when these tires are installed on vehicles other than passenger cars. The reduction in the load rating is intended to provide a safety margin for the generally harsher treatment, such as heavier loading and possible off-road use, that passenger car tires receive when installed on a MPV, truck, bus or trailer, instead of on a passenger car.
FMVSS No. 129, New non-pneumatic tires for passenger cars, 49 CFR 571.129, includes definitions relevant to non-pneumatic tires and specifies performance requirements, testing procedures, and labeling requirements for these tires. To regulate performance, the standard contains performance requirements and tests related to physical dimensions, lateral strength, strength (in vertical loading), tire endurance, and high speed performance. The performance requirements and tests in FMVSS No. 129 were based upon those contained in FMVSS No. 109.
The FMVSS No. 129 labeling requirements are similar to those set forth in section S4.3 of FMVSS No. 109 for size, designation, load, rating, rim size and type designation, manufacturer or brand name, certification, and tire identification number. The standard also includes temporary use and maximum speed labeling requirements and allows methods of permanent marking other than "molding" in anticipation of the difficulty of molding required information on non-pneumatic designs. FMVSS No. 129 initially became effective in August 1990.
IV. Current Safety Problem - Outdated performance requirements
A. Transition from bias ply to radial tires
When FMVSS No. 109 was issued in 1967, nearly all (more than 99 percent) of passenger car tires in the U.S. were of bias, or bias belt construction. The test procedures that appear in FMVSS No. 109 were developed in a bias tire environment. Today, bias tires have been almost completely replaced by radial tires on passenger cars. The use of radial tires has grown to the extent that they represent more than 95 percent of passenger tires in both the U.S.
and Europe and are used on most new light vehicles sold in the U.S. (5) NHTSA does not require radial tires, but regulates their performance through FMVSS Nos. 109 and 119.
Radial tires are less susceptible than bias ply tires to most types of failures. Also, radial tire design resulted in significant improvements in tire performance compared with bias ply tires, thus making it easier for radial tires to comply with the requirements of FMVSS No. 109 than for bias tires.
A bias passenger car tire carcass is typically made up of two or four plies of cord material that run from bead to bead at an angle of approximately 35 degrees to the centerline of the tire. Alternating plies are applied at alternating angles during tire manufacture so that the cord paths of alternating plies criss-cross. This type of construction provides a very strong, durable carcass for the tire. However, it has drawbacks. Because the ply cords criss-cross and all the cords are anchored to the beads, the carcass is stiff and relatively inflexible. This type of construction prevents different parts of the tire from acting independently of one another when forces are applied to the tire. As a result, a bias construction is susceptible to impact breaks because it does not easily absorb road irregularities.
By comparison, a radial passenger car tire carcass is typically made up of one or two plies of cord material that run from bead to bead at an angle of approximately 90 degrees to the centerline of the tire. As a result, the cords do not criss-cross. Because the cords do not criss-cross and because the opposite ends of each cord are anchored to the beads at points that are directly opposite to each other, the radial tire carcass is very flexible. The radial tire is reinforced and stabilized by a belt that runs circumferentially around the tire under the tread. This construction allows the sidewalls to act independently of the belt and tread area when forces are applied to the tire. This "independent" action is what allows the sidewalls to readily absorb road irregularities without overstressing the cords. Impact breaks caused by cord rupture do not occur in radial-ply passenger car tires. This "independent" action also allows two important things to happen during cornering: 1) the tread of a radial tire remains fully in contact with the road over the entire tread width, and 2) the ply cords and sidewall are able to absorb the cornering forces without exerting the twisting force on the beads that are exerted by bias constructions.
These characteristics of a radial tire construction are what make the existing high speed test, endurance test, strength test (6), and bead-unseating test appear to be ineffective in differentiating among today's radial tires with respect to these aspects of performance.
B. Safety Problems Associated with Tires
Tire under-inflation, high ambient temperatures, and vehicle load are among the factors being considered in the ongoing evaluation of the radial tire failures that have occurred in recent years. Data concerning tire failure, blowouts, and rollovers are discussed below.
1. Population of tire related crashes
Several crash files contain information on "general" tire related problems that precipitate crashes. These files are the National Automotive Sampling System - Crashworthiness Data
System (NASS-CDS) (7) and the Fatality Analysis Reporting System (FARS). (8)
NASS-CDS data for 1995 through 1998 indicate that there are an estimated 23,464 tow-away crashes per year caused by blowouts or flat tires.
Estimated Annual Average Number (1995-98 NASS) and Rates of Blowouts or Flat Tires Causing Tow-away Crashes
| Tire Related Cases | Percent Tire Related | |
|---|---|---|
| Passenger Cars Total | 10,169 | 0.31% |
| Rollover | 1,837 (18%) | 1.87% |
| Non-rollover | 8,332 (82%) | 0.26% |
| Light Trucks Total | 13,294 | 0.99% |
| Rollover | 9,577 (72%) | 6.88% |
| Non-rollover | 3,717 (28%) | 0.31% |
| Light Vehicles Total | 23,463 | 0.51% |
| Rollover | 11,414 (49%) | 4.81% |
| Non-rollover | 12,049 (51%) | 0.28% |
Therefore, about one half of one percent of all crashes are caused by these tire problems. The rate of blowout-caused crashes for light trucks (0.99 percent) is more than three times the rate of those crashes for passenger cars (0.31 percent). Blowouts cause a much higher proportion of rollover crashes (4.81) than non-rollover crashes (0.28); and again more than three times the rate in light trucks (6.88 percent) than in passenger cars (1.87 percent).
FARS data for 1995 through 1998 show that 1.10 percent of all light vehicles in fatal crashes were coded with tire problems. Light trucks had slightly higher rates of tire problems (1.20 percent) than passenger cars (1.04 percent). The annual average number of vehicles with tire problems in FARS was 535 (313 passenger cars and 222 light trucks).
2. Geographical and Seasonal Effects
The agency further examined the FARS data to determine whether heat is a factor in tire problems. We examined two surrogates for heat: 1) the region of the U.S. in which the crash occurred, and 2) the season in which the crash occurred. The highest rates of tire problems occurred in light trucks in southern states in the summertime, followed by light trucks in northern states in the summertime, and then by passenger cars in southern states in the summertime. The lowest rates occurred in winter and fall.
Geographical and Seasonal Analysis of Tire Problems (Percent of Vehicles) in FARS with Tire Problems
| Passenger Cars | Light Trucks | All Light Vehicles | |
| Northern States | |||
| Winter | 1.01% | 0.80% | 0.94% |
| Spring | 1.12% | 1.01% | 1.08% |
| Summer | 0.98% | 1.46% | 1.15% |
| Fall | 1.04% | 0.93% | 1.00% |
| Southern States | |||
| Winter | 0.87% | 0.99% | 0.92% |
| Spring | 1.09% | 1.27% | 1.16% |
| Summer | 1.31% | 1.99% | 1.59% |
| Fall | 0.89 | 1.07% | 1.00% |
Winter = December, January, February; Spring = March, April, May; Summer = June, July, August; Fall = September, October, November.
Southern States = AZ, NM, OK, TX, AR, LA, KY, TN, NC, SC, GA, AL, MS, and FL; Northern States = all others.
Based on these data, tires on light trucks appear to be more affected by higher ambient temperatures than tires on passenger cars.
3. Tire Problems by Tire Type and Light Truck Type
The agency also examined tire problems in the NASS-CDS from 1992 to 1999 by types of light trucks and vehicle size to determine whether LT tires used on light trucks exhibited more problems than P-metric tires. LT tires are used on vehicle classes identified for this analysis as Van Large B and Pickup Large B groups of vehicles. These groups of vehicles typically represent the 3/4 ton and 1-ton vans and pick-ups. P-metric tires are used on most of the other light trucks. The data indicate that the average percentage of light trucks in the NASS-CDS having a LT tire problem is 0.84 (10/1,186), while the average percent of light trucks having a P-metric tire problem is 0.47 percent (53/11,226).
Tire Problems by Light Truck Vehicle Type
1992 to 1999 NASS-CDS Unweighted Data (9)
| Light Truck Type | Number of Cases with a Tire Problem | Total Number of Cases | Percent of Cases with a Tire Problem |
|---|---|---|---|
| Van - Compact | 11 | 2,125 | 0.52 |
| Van - Large A | 3 | 431 | 0.70 |
| Van - Large B | 4 | 501 | 0.80 |
| Pickup - Compact | 13 | 3,155 | 0.41 |
| Pickup - Large A | 7 | 1,849 | 0.38 |
| Pickup - Large B | 6 | 685 | 0.88 |
| SUV - Compact | 16 | 3,147 | 0.51 |
| SUV - Large | 3 | 519 | 0.58 |
| Total | 63 | 12,412 | 0.51 |
These larger pickups and vans, however, are also vehicles that carry heavier loads and are more likely to be more overloaded than lighter trucks. In addition, these heavier vehicles are often used at construction sites and may be more apt to encounter nail punctures and experience flat tires. Thus, there may be usage issues that increase the percentage of tire problems for these larger trucks, rather than exclusively a qualitative difference between P-metric and LT tires.
4. Crashes Indirectly Caused by Tire Problems
While the agency has not attempted to estimate the extent to which improved tires would reduce the chance of having a flat tire it has looked at crashes indirectly caused by or involved with tire problems.
The agency has identified several types of such crashes. For instance, if a driver stops his vehicle on the side of the road due to a flat tire, curious passing drivers often slow down to view the incident. This can cause congestion, potentially resulting in a rear impact involving two or more of the passing vehicles toward the rear of the congested traffic. Another crash type indirectly caused by tire problems involves tire repair on the shoulder of the road. Sometimes drivers repairing tires or seeking assistance due to tire problems are struck, as pedestrians, by other vehicles. These phenomena are not captured in NHTSA's data files. However, Pennsylvania, Washington, and Ohio have data files that allow for combining and search for codes for this phenomena; for instance, searching simultaneously for "Flat tire or blowout" and "Playing or working on a vehicle" and "Pedestrians." Our examination of these files for calendar year 1999 for Ohio and Pennsylvania and 1996 for Washington showed the following information:
State Data on Tire Problems and Pedestrians
| Ohio | Washington | Pennsylvania | |
| Pedestrians Injured | 3,685 | 2,068 | 5,226 |
| Pedestrians Injured While Playing or Working on Vehicle | 50 (1.4%) |
27 (1.3%) |
56 (1.1%) |
| Pedestrians Injured While Working on Vehicle with Tire Problem | 0 | 2 | 0 |
| Total Crashes | 385,704 | 140,215 | 144,169 |
The combined percentage of total crashes with tire problems in these three states (3,100/670,088 = 0.46) is consistent with the NASS-CDS data percentage of 0.51 percent. The portion of pedestrians coded as being injured while working on a vehicle with tire problems is 2/10,979 = 0.018 percent. Applying this to the estimated number of pedestrians injured annually across the U.S. (85,000 from NASS-GES) results in an estimated 15 pedestrians injured per year. The agency, however, does not have data to estimate how many pedestrian injuries could be reduced by having better tires.
C. Implications of changes in U.S. light vehicle market
Sales of light trucks have risen steadily for over the past 20 years and now account for almost half of the U.S. light vehicle market - more than twice their market share as recently as 1983. (Industries in Transition, 1/01/00; Journal of Transportation and Statistics, December 2000.) While 9.0 million passenger cars were sold in 2000, the consumer preference for light truck vehicles continued to grow, with sales reaching approximately 8.4 million units, just short of parity with passenger car sales. (Automotive News 2001 Market Data Book). According to analysts and manufacturers, sales of light trucks are expected to surpass sales of cars by approximately 100,000 units this year and the light truck segment is likely to reach "around 60%" before stabilizing. (Auto & Truck Manufacturers Industry Report, 5/15/00).
In addition to purchasing more SUVs, Americans have shifted toward a significantly higher use of minivans, pickup trucks, and SUVs for personal travel. (Journal of Transportation and Statistics, December 2000). The 1995 Nationwide Personal Transportation Survey (NPTS) data set suggests that the average light duty truck (LDT) (pickup trucks, SUVs, and minivans) is used over longer distances and with more people aboard than passenger cars. (10) Additionally, SUVs are popular for long distance weekend travel.
Approximately 90 percent of these light trucks use passenger car (P-metric) tires. The other 10 percent use load range C, D, or E tires which are LT tires and are typically used on heavier light trucks with a gross vehicle weight rating (GVWR) between 6,000 and 10,000 pounds. (11) Sales growth of heavier light trucks, those that have GVWRs above 6,000 pounds, increased at a much faster rate than their lighter counterparts, with larger SUVs (6,000-10,000 pounds GVWR) showing an average increase of 38 percent annually between 1990 and 1998.
V. Agency Response to Safety Problem
A. Relationship Between TREAD Act and Tire Harmonization (Work in UN/ECE's World Forum for Harmonization of Vehicle Regulations (WP.29))
Prior to this rulemaking, NHTSA embarked on a program of global harmonization for light vehicle tire standards under the auspices of the United Nations/Economic Commission for Europe's (UN/ECE) World Forum for Harmonization of Vehicle Regulations (WP.29). (12) NHTSA, within the WP.29's Working Party on Brakes and Running Gear (GRRF) (13), has been working cooperatively with other countries to develop a global tire standard that could better assess the safety performance of modern tires.
In July 1999, NHTSA participated in a GRRF meeting in London, England which initiated deliberations to develop a global technical regulation for tires with other countries. An industry developed standard, Global Tire Standard 2000 for New Pneumatic Car Tires (GTS-2000) (14), was used as a basis for initial discussions on harmonization at that meeting. GTS-2000 would substitute a single high-speed test for the four performance tests in FMVSS No. 109 for most radial tires. (15) More specifically, GTS-2000 would replace the current FMVSS No. 109 high speed test with the high-speed test required by ECE-R30 (the European tire regulation for tires used on light passenger vehicles), including temporary spares. It would also limit the application of the other three tests currently required by FMVSS No. 109, namely the strength test, the bead unseating test, and the endurance test, to bias tires and low speed rated radial tires because industry believes that these three tests have relevance to bias and bias-belted tires, but little, if any, relevance to radial tires, with the single exception of the endurance test for low speed (160 km/h/99 mph, or less) radial tires.
Since the July 1999 meeting, the GRRF has been considering a draft global technical regulation (GTR). Prior to the enactment of the TREAD Act, tentative consensus within an ad hoc tire harmonization working group of the GRRF concerning the draft GTR had been reached on the following issues: 1) to adopt the ECE R30 high speed test methodology (16) in place of the FMVSS 109 high speed test, 2) to keep the current FMVSS 109 resistance-to-bead unseating test until NHTSA develops an alternative that is more appropriate for radial tires, and 3) to develop an optional requirement for testing wet grip. Other issues also under discussion in the ad hoc group prior to the TREAD Act included: a) the U.S.'s suggestion to lower the inflation pressures in and increase the duration of the high speed test (current ECE R30 test), b) the U.S.'s suggestion to agree on the need for tire labeling requirements that are unique to the U.S., such as maximum inflation pressure, and UTQG consumer information, c) the U.S.'s suggestion to identify requirements that should be included as optional requirements, d) assigning to the UN the responsibility for tire plant code registration for a global standard, and e) the U.S.'s suggestion to increase the ambient temperature for the high speed test.
In a February 2001 submission to the docket (Docket No. NHTSA-2000-8011), the Chairman of the GRRF Tire Harmonization Working Group recommended on behalf of the GRRF that NHTSA adopt a draft text that reflects the current state of deliberations for developing a harmonized tire standard.
B. Submissions to NHTSA tire upgrade docket (Docket No. NHTSA-2000-8011)
In September 2000, NHTSA opened a docket, NHTSA-2000-8011, entitled "Tire Testing - Federal Motor Vehicle Safety Standard (FMVSS 109)." The purpose of this docket was to collect tire test data and receive feedback on its high speed and endurance performance testing matrices.
As of the issuance of this document, comments and recommendations from 7 entities have been received in the docket. Substantive comments and recommendations in response to NHTSA's testing matrices are discussed below. Additionally, Toyota Motor Company (Toyota) submitted a copy of its Air Loss Test Procedure.
1. RMA December 2000 Testing Protocol
In December 2000, RMA presented to NHTSA a test protocol (RMA 2000) that was designed and administered with the participation of the following tire companies: Bridgestone/Firestone, Continental/General, Cooper Tire and Rubber, Michelin, Goodyear, Pirelli, Yokohama. The test protocol is divided into the following principal parts: Passenger Car Tire High Speed, Passenger Car Tire Endurance, Light Truck High Speed, and Light Truck Tire Endurance. One hundred thirty-two tests on approximately 900 tires were included in this protocol. A brief summary of RMA 2000's conclusions and recommendations are discussed below.
a. Passenger Tires - High Speed Test
RMA 2000 concluded that
[t]he SAE test [J1561] conditions were found to be the most consistent discriminators required for completion of the rated speed within the customary one-hour duration. (17) Test inflation pressure had the greatest effect in determining completion of the rated speed. Maximum load was also shown to have an effect on performance, although not as great as inflation.
RMA 2000 recommended that the agency revise the High Speed Performance test in FMVSS No. 109 to reflect the conditions found in SAE J1561:
1) Test speed and duration: (Initial Test Speed (ITS) = Tire's rated speed minus 40 km/h), 6 speed steps, each 10 min in duration: 1) 0 to ITS, 2) ITS, 3) ITS + 10 km/h, 4) ITS + 20 km/h,
5) ITS + 30 km/h, 6) ITS + 40 km/h. (18)
2) Inflation pressures (kPa): 240 for speed rating through N, 260 for P, Q, R, & S, 280 for T, U, & H, 300 for V & Z, 320 for W & Y.
3) Load and ambient temperature: 80 percent of maximum rated load, 38C +/-3C.
b. Passenger Tires - Endurance Test
RMA concluded that "the results seem to indicate that speed, followed closely by inflation pressure, are key determinants affecting the number of hours to failure."
RMA recommended revising the Endurance test in FMVSS No. 109 to include the following parameters:
1) Inflation pressure: 180 kPa.
2) Test speed: constant at 120 Km/h.
3) Duration and load: 8 hours at 85 percent of maximum rated load, 8 hours at 90 percent of maximum rated load, 8 hours at 100 percent of maximum rated load.
4) Ambient temperature: 38C +/- 3C.
c. Light Truck Tires - High Speed Test
RMA concluded that
[f]or load range C tires an analysis of the results shows the maximum load conditions of 90 percent to be more realistic than the 80 percent. Also, it appears that the inflation pressure of 350 kPa is the most suitable for this test. For load range E tires the data showed that conditions of 90 percent maximum load and 550 kPa pressure, while not particularly discerning for the Q speed rated tires did become much more rigorous for the R speed rated tires (no S rated tires were included in the load range E tests).
RMA recommended that NHTSA incorporate a test similar to SAE J1633 or ISO 10454 into its light truck tire standard, using maximum inflation pressure, limited to tires marked "LT" or "C" and load range A-E or Load Index 124 or below. The parameters are as follows:
1) Speed and duration (ITS= Tire's rated speed -20 km/h): 3-speed steps: 0 to ITS for 10 min, ITS for 10 min, ITS + 10 km/h for 10 min, ITS + 20 km/h for 30 min.
2) Inflation pressure corresponding to maximum load.
3) Load: 90 percent of maximum.
4) Ambient temperature: 38C +/-3C.
d. Light Truck Tires - Endurance Test
RMA 2000 concluded that
[a]s with passenger car endurance tests, speed is deemed to be the greatest determinate of tire failure, followed closely by inflation pressure...In the FMVSS 119 test it wasn't until load limits became unrealistically high that tires begin to fail. However, in the four test protocols using combinations of the test conditions cited above, average hours to failure were more realistically demonstrated when testing at 120 km/h using the inflation pressures corresponding to the maximum load rating marked on the tire (350 kPa for load range C, and 550 kPa for load range E).
RMA 2000 recommended revising the light truck tire standard to include the following test parameters:
1) Inflation pressure: at pressure corresponding to the maximum load rating marked on the tire.
2) Speed: constant at 120 Km/h.
3) Duration and load: Load range A, B, C, & D for 8 hours at 75 percent of maximum rated load, 8 hours at 97 percent of maximum rated load, and 8 hours at 114 percent of maximum rated load. Load Range E for 8 hours at 70 percent of maximum rated load, 8 hours at 88 percent of maximum rated load, and 8 hours at 106 percent of maximum rated load.
4) Ambient Temperature: 38C +/-3C.
2. Other Substantive Submissions
In February 2001, Michelin presented its suggested Endurance Certification Test to NHTSA. This is an endurance test for long term durability, which evaluates the following factors: belt edge stress, long-term cyclic fatigue and compound evolution. The following table illustrates the parameters of this test:
| Metric Passenger Car | Light Truck | |||||
| Load Range | Standard Load | Extra Load | B | C | D | E |
| Test Temperature (F) | 100+/-5 | 100+/-5 | ||||
| Speed (mph) | 60 | 60 | ||||
| Filling Gas | 50%O2/50%N2 | 50%O2/50%N2 | ||||
| Load (lbs) - % Max Single | 111 | 142 | 112 | 98 | 92 | |
| Initial Pressure (psi)- Regulated | 40 | 46 | 57 | 57 | 65 | 80 |
In May 2001, Michelin supplemented its requested endurance test with a discussion of the influence of its long term durability endurance test variables on tire endurance and crack propagation.
Michelin has also recommended replacing the current high speed test with ISO 10191. ISO 10191 contains test variables substantially similar to those in SAE J1561 and those recommended by RMA 2000 for the high speed test for passenger tires.
In a November 2000 submission to the docket, GM provided the following general comments on the first phase of NHTSA's tire testing matrix: 1) increased high speed capability will result directly in compromises with mass, fuel economy (rolling resistance) and ride comfort, 2) correlation of laboratory tests with performance of tires in the field environment is necessary and tires with known acceptable field performance should serve as reference to acceptable performance on such laboratory tests, 3) tests that take the tire to failure can always be developed but may not indicate poor performance and tire failures on these tests should not be interpreted as an indication of unacceptable performance, 4) the definition of failure for these tests should be clarified, and 5) it is recommended that temperature monitoring be included in the testing.
GM also submitted a number of comments on NHTSA's test matrices. These comments, specific to NHTSA's preliminary test parameters, are not discussed in detail here, but are available for review in the docket.
C. NHTSA tire testing at Standards Testing Lab (STL)
Shortly after the enactment of the TREAD Act, the agency initiated tire testing at Standards Testing Labs (STL) in November 2000 to evaluate the high-speed performance, endurance performance, and low inflation pressure performance of a limited number of current production tires. The agency developed a test matrix which focused on the five main parameters currently used in tire testing under FMVSS Nos. 109 and 119: load, inflation pressure, speed, duration, and ambient temperature. Copies of the test matrix and testing results for P-metric tires and for LT tires is available in the docket (see the Tire Test Matrix in NHTSA Docket No. 2000-8011-1).
1. High Speed Testing
The high speed tests included a wide range of values for the test parameters to facilitate evaluation of the performance of a variety of tires used on light vehicles. A baseline high speed test was performed on each of the tire brands using the GTS-2000 high speed test for P-metric tires and FMVSS No. 109 for the LT tires. (19)
The Phase I test matrix included loads of 80, 90, and 100 percent (20); inflation pressures of 180 kPa, 210 kPa and 240 kPa; durations at each speed step of 10 minutes, 20 minutes and 30 minutes; and four speeds steps beginning at an initial test speed (ITS) 30 km/h below the rated speed of the tire, and increasing in 10-km/h increments up to the rated speed (ITS + 30km/h). Some tests were conducted to failure, beyond the rated speed of the tires, to assess the performance margin for the tires. In this phase of testing, nine P-metric tire brands and three LT tire brands were tested using 28 tires per brand, one tire for each of the 28 high speed tests performed. The total number of tires tested to the high speed test in this phase was 336 tires.
The test results from the Phase I tests show that all but one of the tires completed the baseline high speed tests up to their rated speed without failure. The results of the matrix tests indicate that all the parameters have an impact on tire failure in the high-speed test; however, a decrease in inflation pressure appeared to have the greatest impact on time to failure in the high-speed test. For example, at an inflation pressure of 180 kPa using 20-minute speed intervals, the results of the P-metric tire tests indicate 3 of 9 tire failures, while at 240 kPa, under similar test conditions, all 9 tires completed the high speed test. The data also indicate that RMA 2000's suggested 10-minute test duration at each speed appears to be too short to properly evaluate the high speed performance of a tire. In the agency's testing, few failures occurred at the 10-minute steps, and all tires tested were able to complete many of the tests conducted using 10-minute speed intervals. In general, the most stringent mix of parameters was 100 percent load, low inflation pressure of 180 kPa, combined with the longest test duration for each speed step, 30 minutes. This test condition resulted in only one of nine P-metric tires completing the high speed test. A similar test condition for the test on three LT tires resulted in one tire completing the high speed test. The agency notes that these severe test conditions enabled us to evaluate the high speed performance limits of some current production tires.
The agency conducted additional high speed testing using a Phase II matrix. This second phase of the high-speed testing included 12 tire brands (8 P-metric and 4 LT tires) with a sample of five tires per test per brand. The test parameters included loads at 80 and 85 percent; inflation pressures at 210 kPa and 220 kPa; duration of 20 minutes; and speeds similar to the ITS plus 10, 20, 30 km/h method used in Phase I, and also three fixed speeds of 160, 170, and 180 km/h for 30 minutes at each speed step. For the LT tires tested to the high-speed test, the parameters were similar as those used for P-metric tries, except that the inflation pressures were changed to reflect the higher maximum inflation pressures on those tires.
The test results from the second phase testing demonstrated that there is variability in the manufacturing quality of tires since a mix of passes and failures occurred within the 5 samples tested for each brand.
2. Endurance Testing
The endurance testing was also comprised of two phases of matrix testing. The baseline endurance test used for the P-metric tires was the one in GTS-2000 for radial tires rated "Q" or below. For LT tires, the FMVSS No. 119 endurance test was used as the baseline. The agency also conducted endurance testing with load combinations of 100/115/125 percent load, test speeds of 120 and 140 km/h, inflation pressures of 160 kPa and 200 kPa for P-metric tires, and for a duration of 50 hours. Similar parameters were used for LT tires, except with different inflation pressures since these tires have higher maximum inflation pressures than P-metric tires.
All the tires completed the baseline endurance tests without any failures. The results of the matrix tests for endurance indicate that the higher test speed, 140 km/h, had a large impact on the time to failure, even at the higher inflation pressure of 200 kPa. The high load percentages also contributed significantly to the short time to failure, especially for some of the LT tires.
The second phase of the endurance testing included test parameters closer to those that the agency is proposing in this NPRM. The parameters were as follows: lower loads of 100/110/115 percent combined with a test speed of 120 km/h at 180 kPa inflation pressure for a duration of 50 hours; higher loads of 100/115/125 percent combined with a lower test speed of 100 km/h at 180 kPa inflation pressure for 50 hours.
The results of the second phase of endurance testing indicate that fewer failures occurred in Phase II testing with the combination of high load (100/115/125 percent) and lower speed (100 km/h) than under the parameters of Phase 1 testing. In Phase 2, 7 of the 8 P-metric tires completed the test without any failures in any of the 5 samples of each brand tested. The 4 LT tires tested also performed well with one failure in the five samples in 3 of the 4 brands tested. One brand completed the test with all 5 tires completing the 50-hour test. The test conditions that produced the most failures in the P-metric tires were the higher load combinations at 120 km/h. These conditions, surprisingly, did not produce many failures in the LT tires tested.
3. Low Inflation Pressure Testing
The agency also conducted a test at low inflation pressures (140 kPa (20 psi) inflation pressure for P-metric tires), at a speed of 120 km/h (75 mph) for a duration of 90 minutes, on the same tires (2 samples of each of the 12 brands) that successfully completed the endurance test. The purpose of this test was to evaluate tire performance at a low inflation pressure threshold level, 20 psi, being proposed for tire pressure monitoring systems for light vehicles. (21) Similar tests were performed using the LT tires, but at low inflation pressures values commensurate with 58 percent of their maximum inflation pressure. These low threshold values were selected based on the lowest inflation pressure at which a tire load is provided by the tire industry standardizing bodies. The test results indicate that all 24 tires tested completed the 90 minute test low inflation pressure test without failure.
4. Conclusions from Testing Results
In summary, the results of the high speed and endurance tests indicated that the agency can develop and propose test requirements that are realistic in terms of the test parameters, yet more stringent than the current FMVSS No. 109, FMVSS No. 119 requirements, European Regulation ECE R 30, GTS 2000, and RMA 2000. The proposed test requirements differentiate tires with better high speed and endurance performance from those with lesser performance. The low pressure validation tests indicate that tires that were able to successfully complete the endurance testing can also complete an additional 90-minute test at a low inflation pressure, 140 kPa for P-metric tires, thus providing an adequate safeguard for consumers to take corrective action when the low pressure warning lamp proposed under the tire pressure monitoring system rulemaking is activated at a "significantly" under-inflated level.
VI. Agency Proposal
A. Summary of Proposal
The agency is proposing a single standard for light vehicle tires, FMVSS No. 139, New Pneumatic Tires for Light Vehicles, which would require light vehicle tires to meet a high-speed test, an endurance test, a low inflation pressure performance test, a resistance-to-bead unseating test, a road hazard impact/strength test, and an accelerated aging test. This standard would require tires for passenger cars, multipurpose passenger vehicles, trucks, buses and trailers with a gross vehicle weight rating (GVWR) of 4,536 kilograms (10,000 pounds) or less, manufactured on or after November 1, 2003, to comply with the test requirements. Therefore, this proposal is applicable to LT tires up to load range E. (22) The following chart compares the types of test requirements that currently exist, those that have been suggested by third parties, and those are being proposed by this agency:
TABLE 1 - COMPARISON OF TYPES OF TIRE PERFORMANCE REQUIREMENTS IN VARIOUS EXISTING AND DRAFT TIRE STANDARDS
| TESTS | FMVSS 109 |
FMVSS 119 |
GRRF Draft GTR |
GTS-2000 | RMA 2000 |
ECE R30 |
PROPOSED FMVSS 139 |
|---|---|---|---|---|---|---|---|
| High Speed | X | - | X† | X | X | X | X |
| Endurance | X | X | X* | X** | X | - | X |
| Low pressure performance |
- | - | - | - | - | - | X |
| Strength; or Road Hazard Impact |
X - |
X - |
- | - | - | - | - X |
| Bead Unseating |
X | - | X*** | - | - | - | X |
| Accelerated Aging |
- | - | - | - | - | - | X |
Both the proposed High Speed Test and the Endurance test contain testing parameters (ambient temperature, load, inflation pressure, speed, and duration) that make the tests more stringent than those tests currently found in FMVSS Nos. 109 and 119, as well as the tests suggested by industry. Most significantly, the proposed High Speed test specifies test speeds (140, 150 and 160 km/h (88, 94, and 100 mph)) substantially higher than those specified in FMVSS No. 109 (120, 128, 136 km/h (75, 80, 85 mph)). Likewise, the proposed Endurance Test specifies a test speed 50% faster (120 km/h (75 mph)) than that currently specified in FMVSS 109 (80km/h (50 mph)), as well as a duration 6 hours longer (40 hours total) than that currently specified in FMVSS 109 (34 hours total). At the specified test speed (120 km/h), the Proposed Endurance Test mileage (3,000) is almost double the mileage that a tire endures under the current Endurance Test (1,700 miles at 80 km/h).
The proposal also contains two alternative Low Inflation Pressure tests which seek to ensure a minimum level of performance safety in tires when they are underinflated to 140 kPa. The agency requests comments on which test is more appropriate to be included in the new standard.
In place of the current strength test in FMVSS No. 109, the agency proposes that the new standard contain a Road Hazard Impact test which is modeled after a SAE recommended practice. This test, which simulates a tire impacting a road hazard, such a pothole or curb, provides both a more stringent and more real world test than the FMVSS No. 109 "plunger test."
The proposal would also replace the current FMVSS No. 109 Bead Unseating Test with a new Bead Unseating test which is based on a test currently used by Toyota. Industry has previously recommended to the agency that the current bead unseating test be deleted from the standard because radial tires are easily able to satisfy the test. Results from the agency's 1997-1998 rollover testing, however, provide a strong rationale for upgrading, rather than deleting, the bead unseating requirement in FMVSS No. 109. The Toyota test uses test forces more stringent than those in current FMVSS No. 109 which were developed for bias ply tires and are typically not stringent enough for radial tires.
To address the deterioration of tire performance caused by aging, the proposal contains three alternatives for an Aging Effects Tests. These tests, the Adhesion (Peel) Test, Michelin's Long-term Durability Endurance test, and Oven Aging all seek to expose tires to the type of failures experienced by consumers at 40,000 kilometers or beyond. The agency requests comments on which test is most appropriate to be included in the new standard.
The proposal would also revise FMVSS Nos. 110 and 120 to reflect the applicability of the new standard and would revise certain of the tests in FMVSS Nos. 117 and 129 to ensure that all light vehicle tires are required to comply with the identical minimum performance requirements. Lastly, the proposal discusses NHTSA's ongoing and future Road Hazard Impact Test and Bead Unseating Test research plans, the lead time for implementation of the new tire standard, the use of shearography analysis, and the revision of the requirements for the test speeds in UTQG Temperature Grading Requirement to mirror those in the proposed High Speed Test.
NHTSA believes that the proposed upgraded standard would specify more stringent and real-world, yet practicable, tests that would provide a higher level of operation safety and performance for tires on today's light vehicles.
B. Applicability
FMVSS No. 139 would apply to new pneumatic tires for use on motor vehicles with a GVWR of 10,000 pounds or less, manufactured after 1975, except for motorcycles. Given the increasing consumer preference for light truck use for passenger purposes, the agency is proposing that the safety requirements for passenger car tires also be made applicable to LT tires (load range C, D, and E) used on light trucks.
Currently, the performance requirements for LT tires in FMVSS No. 119 are less stringent than the requirements for P-metric tires in FMVSS No. 109. LT tires are required to comply with a strength test and a low speed endurance test, but are not required to be tested to a high speed performance test or a resistance-to-bead unseating test as required under FMVSS No. 109. However, LT tires are increasingly used in the same type of on-road service as P-metric tires on light vehicles. Further, recent sales data for heavier light trucks indicate that the use of these tires on passenger vehicles will continue to increase in the near future.
NHTSA is not proposing to require that FMVSS No. 139 apply to motorcycle tires because motorcycle tires are of a design and construction unlike the types of vehicle tires that would be subject to the proposed standard (e.g, tread, load carrying capacity) and motorcycle tires still often use inner tubes. Further, the agency is not currently aware of any safety problems associated with motorcycle tires.
NHTSA is also not proposing to require that the new standard be applicable to tires beyond load range E, which are typically used on medium (10,001-26,000 lbs. GVWR) and heavy (greater than 26,001 lbs. GVWR) vehicles, and temporary spare tires, (23) for two reasons. This rulemaking is required by the TREAD Act, and must be completed by June 2002. To meet this statutory deadline, the agency has limited its tire upgrade research and analysis to conventional tires for light vehicles. The issues associated with upgrading performance standards for tires on medium and heavy vehicles and temporary spare tires are different from the issues associated with upgrading performance standards for conventional tires on light vehicles. For example, medium and heavy vehicles are equipped with tires that are much larger and have higher pressure levels than the tires used on light vehicles. Temporary spare tires are smaller, have higher inflation pressures, and are intended for shorter distance and lower speed driving than conventional light vehicle tires. Given the TREAD Act deadline on this rulemaking, the agency does not have the time to study and analyze sufficiently the different issues presented by medium and heavy vehicle tires and temporary spare tires. NHTSA will examine these types of tires after we have completed this rulemaking.
C. Proposed Test Procedures
1. High Speed Test
NHTSA proposes that the High Speed test be conducted using the following five parameters:
A tire complies with the proposed requirements if, at the end of the high speed test, there is no visual evidence of tread, sidewall, ply, cord, inner liner, or bead separation, chunking, broken cords, cracking, or open splices, and the tire pressure is not less than the initial test pressure.
The agency proposes a high speed test with three pre-selected speeds. This testing methodology is different from that in two alternatives which were considered by the agency: 1) GTS-2000, and 2) a high speed test using identical parameters to those proposed above, except that the test speeds are based on the rated speed of the tire (initial test speed (ITS), ITS + 10, ITS + 20, ITS + 30) for durations of 20 minutes at each speed step with a 10-minute warm-up from 0 km/h - ITS. (24)
The methodology suggested by the tire industry in GTS-2000 for tire harmonization and the second alternative determines the test speed based on the tire's speed symbol rated speed. The following chart illustrates the rated speed in km/h for each speed symbol.
| Speed Symbol | Rated Speed - km/h | Speed Symbol | Rated Speed - km/h |
| F | 80 | R | 170 |
| G | 90 | S | 180 |
| J | 100 | T | 190 |
| K | 110 | U | 200 |
| L | 120 | H | 210 |
| M | 130 | V | 240 |
| N | 140 | W | 270 |
| P | 150 | Y | 300 |
| Q | 160 | ZR | > 300 |
The initial test speed (ITS) in GTS-2000 is the rated speed of the tire minus 40 km/h. The test is conducted at the following speed steps: ITS, ITS+10 km/h, ITS+20 km/h, ITS+30 km/h and ITS+40 km/h. The final speed step, ITS+40 km/h, is identical to the rated speed of the tire. Similarly, the ITS in the second alternative is the rated speed of the tire minus 30 km/h. The test is conducted at the following speed steps: ITS, ITS+10 km/h, ITS+20 km/h, and ITS+30 km/h, with the final speed step being identical to the rate speed of the tire. Therefore, under both alternatives, each tire with a different speed rating is tested at different speeds during the high speed test.
Historically, the agency establishes uniform minimum performance requirements for its safety standards for the item of motor vehicle equipment. Testing for compliance using the tire's rated speed differs from that philosophy since it does not establish a single absolute minimum requirement for all tires, but establishes a relative requirement based on each tire's maximum design capabilities.
The agency's proposal, based on pre-selected test speeds and independent of the rated speed of the tire, establishes the same minimum requirement for all tires, regardless of the designed level of performance. We believe that such a methodology is equitable for all tire manufacturers and does not impose higher safety standard requirements on a tire with a higher level of performance.
The following table illustrates an at-a-glance comparison of the other standards and suggestions discussed in this document. (25)
TABLE 2 - HIGH SPEED TEST COMPARISON
| TEST PARAMETERS | FMVSS 109 |
GTS 2000 | RMA 2000 |
ECE 30 | Proposed FMVSS 139 |
|---|---|---|---|---|---|
| Ambient (oC) | 38 | 25 | 38 | 25+5 | 40 |
| Load (%) | |||||
| P-metric | 88 | 80 | 80 | 80 | 85 |
| LT | - | - | 90 | ||
| Inflation Pressure (kPa) | |||||
| Standard load P-metric | 220 | - | - | - | 220 |
| Extra load P-metric | 260 | - | - | - | 260 |
| LT load range C/D/E | - | - | sidewall max | - | 320/410/500 |
| SpeedRating (Std/Extra) | - | ||||
| L,M,N | - | 240/280 | 240/280 | - | - |
| P,Q,R,S | - | 260/300 | 260/300 | 260/300 | - |
| T,U,H | - | 280/320 | 280/320 | 280/320 | - |
| V | - | 300/340 | 300/340 | 300/340 | - |
| W,Y | - | 320/360 | 320/360 | 320/360 | - |
| Test speed* (km/h) | 120, 128, 136 | 0-ITS, ITS, +10, +20, +30 | 0-ITS, ITS, +10, +20, +30, +40 | ITS, +10, +20, +30 | 140, 150, 160 |
| Duration (mins) | 90 | 60 | 60 | 60 | 90 |
An explanation of the proposed parameters is provided below.
a. Ambient temperature
The proposed ambient temperature is 40C. This temperature is a slight increase over the temperature, 38C, currently specified in FMVSS No. 109. This temperature reflects the typical daytime temperatures in the South and Southwestern regions of the U.S. during the Summer. As discussed earlier, the highest rates of tire problems occurred in the southern states in the summertime.
b. Load
The load proposed for the high-speed test is 85 percent. The load percent currently specified in FMVSS No. 109 is 88 percent. As discussed in greater detail below, decreasing the load from 88 percent to 85 percent increases the tire reserve needed by a vehicle under normal loading conditions from 12 percent to 15 percent, resulting in a larger margin of safety when a vehicle is loaded to its GVWR or its tires are underinflated.
Changing the load from 88 percent to 85 percent in the high speed test would affect the current requirement in S4.2.2 of FMVSS No. 110 which states that the vehicle normal load on the tire is to be no greater than the applicable load used in the high speed performance test. "Tire reserve load" refers to a tire's remaining load-carrying capability when the tire is inflated to the vehicle manufacturer's recommended inflation pressure and the vehicle is loaded to its gross vehicle weight rating (GVWR). (26) When a tire is loaded to 88 percent of the maximum load labeled on the tire sidewall, the unused 12 percent is considered the reserve load of the tire under normal loading conditions (curb weight of the vehicle plus three occupants in a vehicle with a designated seating capacity of five or more.) A change from 88 percent to 85 percent load on the tire for the high speed test would, in essence, require a vehicle manufacturer to increase the reserve load under normal loading from 12 percent to 15 percent. This requirement may, in turn, necessitate the use of a larger tire size on some vehicles since the load limit on existing tires may not be sufficiently high to provide a load reserve of 15 percent of the tire's maximum rated load.
In addition, the requirement for a 12 percent tire reserve under normal loading conditions currently applies only to passenger cars. This notice proposes to require light trucks for the first time to have a specified tire reserve under normal loading conditions. Light trucks would have to provide the same 15 percent reserve proposed for passenger cars.
The agency also proposes revised language in FMVSS No. 110 to clarify that the test load that is compared with the vehicle normal load must be determined at the vehicle manufacturer's recommended cold tire inflation pressure, and not at the maximum tire load limit on the sidewall. The agency believes that since the vehicle normal load defines loading during normal operation of the vehicle, it is appropriate to require the load to be determined at the vehicle's recommended cold tire inflation pressure. (27)
Although 85 percent loading for the high speed testing of tires represents a slight decrease from the current 88 percent specification in FMVSS No. 109, test data from the agency's testing and from RMA testing indicate that tire failure is more sensitive to speed and inflation pressure than to loading variations in the 80 to 90 percent range. (28) The agency believes that a speed increase from 75, 80 and 85 mph to speeds up to 160 km/h (100 mph) would contribute to a more stringent test which would more than offset a small decrease in test load requirements. In Phase I of the agency's testing, 5 of 9 P-metric tires failed at 90 percent load and 2 of 9 failed at 80 percent. Phase II of the testing included testing of 8 P-metric tire brands, 5 samples each, at 80 and 85 percent loads, and with all other test parameters remaining constant (inflation pressure - 220 kPa, 20 - minute steps, speeds ITS to ITS + 30 km/h). In these tests, fewer tire failures occurred at 85 percent load than at 80 percent load. (29) At 85 percent load, 5 of 8 tire brands had no tire failures in their 5 samples and the other three brands had at least one failure in the five samples. One brand experienced failures in all 5 samples tested to the high speed test. Four brands of LT tires were also tested and all samples for each of the brands completed the high speed test at 85 percent load without any failures. This testing appears to confirm that small increases in tire load have less of an impact on time to failure as compared with changes in inflation pressure and test speed.
c. Inflation Pressure
The agency proposes a test inflation pressure of 220 kPa (32 psi) for all unrated and speed rated P-metric tires and 260 kPa for extra load tires. The proposed P-metric tire pressure is the same as that specified in FMVSS No. 109. The agency proposes the following inflation pressures for LT tires based upon their higher maximum inflation pressures: 320 kPa for load range C, 410 kPa for load range D, and 500 kPa for load range E tires. During its testing, the agency incorrectly used 600 kPa as the maximum load rate inflation pressure for LT tires with load range "E", and calculated test pressures utilizing 600 kPa. Based on the Tire and Rim Association (T&RA) Yearbook, load range E tires have an inflation pressure of 550 kPa at its maximum load rating. Therefore, the test inflation pressures are revised accordingly.
The proposed inflation pressures are based on surveys showing that tires are typically operated at some level of underinflation. (30) Given the tire pressure survey data, the agency selected the proposed test pressures based on the level of underinflation experienced during normal vehicle operation. The 220 kPa value represents an under-inflation of 20 kPa (3 psi) or 8 percent from the 240 kPa maximum inflation pressure, and 260 kPa represents an under-inflation of 20 kPa (3 psi) or 7 percent from the 280 kPa maximum inflation pressure.
Although 220 kPa is the same test pressure specified in FMVSS No. 109, this test pressure, in conjunction with the new proposed test speeds, represents a more stringent test than that contained in FMVSS No. 109. Agency testing results indicate that 220 kPa is a test inflation pressure that would be appropriate for the high speed test given the parameters of speed, load and test duration.
RMA suggested basing the test inflation pressure on the rated speed of the tire. Tires rated P, Q, R, and S would be tested at 260 kPa; tires rated T, U, H are tested at 280 kPa; tires rated V are tested at 300 kPa; and tires rated W, Y, and Z are tested at 320 kPa. (31) The agency believes that these inflation pressure values are too high for high speed testing because 1) they do not reflect values that are similar to the cold inflation pressures recommended by vehicle manufacturers, and 2) they do not correspond well with the real-world inflation pressures recently obtained from the vehicles measured during a recent NHTSA sponsored consumer tire pressure survey. (32) Further, the agency has stated in previous rulemakings that standard load tires with higher maximum inflation pressures (300 and 350 kPa) are not capable of carrying additional load at higher inflation pressures beyond 240 kPa. They should be tested at an inflation pressure similar to that of the 240 kPa maximum inflation pressure tires. (53 FR 17950, 5/19/88; 53 FR 936, 1/18/88)
d. Speed
The proposed test speeds, 140, 150 and 160 km/h (88, 94, and 100 mph) represent a substantially increased stringency from the test speeds currently used in FMVSS No. 109 and 119 for which tires are tested at 75, 80, and 85 mph for 30 minutes at each speed. This approach would more closely mirror the upper limit of real world operational speeds beyond which drivers have few opportunities to operate their vehicles and eliminate from production any tires whose production just achieved the lowest rung of Temperature resistance rating in our Uniform Tire Quality Grading System (UTQGS), "C" rated tires.
The agency considered proposing a higher threshold test speed of 180 km/h so that speed rated tires with a speed rating lower than "S' (180 km/h) would not have been able to comply with the high speed test. In the U.S., light vehicles are typically equipped with tires speed rated no lower than Q (160 km/h). GM suggested that the agency consider basing our test speed on the speed rating of the tire since many of their light trucks are equipped with LT tires rated Q and R, 160 km/h (100 mph) and 170 km/h (106 mph), respectively. NHTSA, however, believes that an upper test speed threshold of 160 km/h (100 mph) ensures a minimum level of safe operation that is 25-30 mph beyond typical speed limits on interstate highways in the U.S.
Under the UTQG test procedure, a tire is rated C if it fails to complete the test at 100 mph for 30 minutes. The test is initiated at 75 mph for 30 minutes and then successively increased in 5 mph increments for 30 minutes each until the tire has run at 115 mph for 30 minutes. Therefore, tires with a temperature rating of C would be able to complete 30 minutes at speeds of 75, 80, 85, 90, and 95 mph (120, 128, 136, 144, and 152 km/h), but not complete the 100-mph (160 km/h) step. NHTSA, as mentioned above, believes that testing at an upper test speed threshold of 160 km/h (100 mph) ensures a minimum level of safe operation.
As discussed above, NHTSA used test speeds based on the speed rating of the tires for its high speed testing at STL (see the Tire Test Matrix in Docket No, NHTSA-00-8011-1). While representing a departure from the methodology of utilizing three predetermined test speeds (as proposed above and currently used in the FMVSS Nos. 109 and 119 high speed tests), this approach is identical to that contained in ECE R 30, GTS-2000, RMA 2000, and in SAE Recommended Practice J15161, Laboratory Speed Test Procedure for Passenger Car Tires. NHTSA seeks comment on whether test speeds based on speed ratings would be more appropriate, than those proposed above, for the High Speed Test and, more specifically, whether the method for determining test speeds contained in NHTSA's high speed testing matrix or the two alternatives mentioned above would be appropriate for the High Speed Test in the final rule.
e. Duration
NHTSA proposes a 30-minute test duration for each of the 3 speed steps, 140, 150, and 160 km/h. The total test time equals 90 minutes. The 30-minute duration allows the tire to attain and maintain its operating temperature at each speed step so that the tire's performance could be evaluated during a steady rate of speed for a duration longer than 10 minutes.
Based on its testing, the agency believes that RMA 2000's 10 minute duration at each speed step (10 minute speed build-up from 0 km/h to ITS, then five 10 minute speed steps) is too short to provide a proper evaluation of high-speed performance. Very few failures occurred in the agency's testing using the 10-minute duration for speed steps. Additionally, RMA's recommendation reduces the duration currently specified in FMVSS No. 109 by almost 50 percent.
3. Endurance Test
NHTSA proposes that the Endurance test be conducted using the following five parameters:
A tire complies with the proposed requirements if, at the end of the endurance test, there is no visual evidence of tread, sidewall, ply, cord, inner liner, or bead separation, chunking, broken cords, cracking, or open splices, and the tire pressure is not less than the initial test pressure.
This combination of these parameters for P-metric tires represents a more real-world test and an increase in stringency over FMVSS No. 109's endurance test with an 18 percent increase in the duration, a 10 percent increase in the load, and a 50 percent increase in speed.
Two alternatives to the proposed test parameters were considered by the agency: 1) RMA 2000, and 2) an endurance test using identical parameters to those proposed above except for test loads at 100/110/115 percent for durations of 8, 10, 32 (total 50).
RMA 2000 includes no change in the load combination of 85/90/100 percent and a 10-hour (almost 30%) decrease in duration from the current standard, FMVSS No. 109. The load and duration increase of the second alternative to a load combination of 100/110/115 and a 16-hour (almost 50%) increase in duration from FMVSS No. 109 would fail over 40 percentage of P-metric tires and 20 percent of LT tires tested. (33)
The agency proposes an endurance test that has parameters different from the two alternatives in load and duration. The agency believes that, given the change in the composition of the light vehicle market in the U.S. over the past 10 years towards a greater proportion of light trucks and vans being used for passenger purposes, the load values for an endurance tire test should be increased up to 110 percent to reflect the greater likelihood of vehicle overloading that is more likely to occur with light trucks and vans than with passenger cars. Further, the agency believes that an increase in duration for the test is warranted reflecting the increased life of today's tires. The increase in duration from 34 hours to 40 hours combined with the proposed test speed of 120 km/h represents an increase in the total test distance from 2720 km (1700 miles) to 4800 km (3000 miles).
The following chart illustrates an "at-a-glance comparison" of the proposed standard to the other standards and suggestions discussed in this document. (34)
TABLE 3 - ENDURANCE TEST
| TEST PARAMETERS |
FMVSS 109 |
FMVSS 119 |
GTS-2000* | RMA 2000 | ECE R30 |
New FMVSS 139 |
|---|---|---|---|---|---|---|
| Ambient (oC) | 38 | 38 | 38 | 38 | N/A | 40 |
| Load (%) | ||||||
| P-metric | 85/90/100 | - | 100/110/115 | 80/90/100 | N/A | 90/100/110 |
| LT-load C/D | - | 75/97/114 | - | 75/97/114 | N/A | 90/100/110 |
| LT-load E | - | 66/84/101 | - | 70/88/106 | N/A | 90/100/110 |
| Inflation Pressure (kPa) | ||||||
| Standard load P-metric | 180 | - | 180 | 180 | N/A | 180 |
| Extra load P-metric | 220 | - | 220 | 220 | N/A | 220 |
| LT-load C/D | - | sidewall max | - | sidewall max | N/A | 260/340 |
| LT-load E | - | sidewall max | - | sidewall max | N/A | 410 |
| Speed (km/h) | 80 | 80 | 80 | 120 | N/A | 120 |
| Duration (hrs) | 34 | 34 | 34 | 24 | N/A | 40 |
The endurance testing conducted in Phase 1 of the agency's testing was performed at 120 km/h and 140 km/h, with loads of 100 percent, 115 percent, and 125 percent for a total of 50 hours, and at inflation pressures of 160 kPa and 200 kPa. Many failures occurred at the combination of low inflation pressure (160 kPa) and high speed (140 km/h). At a test speed of 120 km/h with an inflation pressure of 200 kPa, 2 of the 9 P-metric tires failed to complete the 50 hour test.
In Phase 2 of the testing, the agency tested with loading conditions of 100/110/115 percent, (identical to the load recommended by the tire industry for the endurance test in GTS-2000), 180 kPa inflation pressure, 120 km/h for 50 hours. For P-metric tires, 2 of the 8 tire brands completed the test without any failures in their 5 samples; the remaining tire brands experienced at least one failure in the five samples used during the test.
Although neither phase of the endurance testing tested tires at exactly the same conditions as those proposed above, analysis conducted by the agency indicates that 19 of the 24 tires tested would pass the proposed endurance test. This analysis is contained in the PEA. NHTSA seeks comment on this analysis and whether the two alternatives mentioned above would be appropriate for the Endurance Test in the final rule.
A more detailed explanation of the proposed parameters is discussed below.
a. Ambient temperature
The proposed ambient temperature is 40C. This temperature is a slight increase over the temperature, 38C, currently specified in FMVSS No.109, and reflects typical daytime temperatures in the South and Southwestern regions of the U.S. during the Summer months. As discussed earlier, the highest rates of tire problems occurred in the southern states in the summertime.
b. Load
The proposed loads for the endurance test are 90, 100, and 110 percent. These load percentages represent an approximate 10 percent increase over the load percentages specified for the endurance test in FMVSS No. 109 (85, 90, and 100 percent) and an increase over those recommended by RMA 2000.
The load levels originally proposed by the tire industry in GTS-2000 for P-metric tires rated Q or below were 100/110/115 percent at a test speed of 80 km/h. Given the increased use of light trucks and vans by the general public and the larger cargo volumes available in these vehicles, the agency believes that they are more likely to be operated in an overloaded condition than passenger cars. Our proposal for loads in the endurance test, 90/100/110 percent, reflects the need to increase the loads beyond the loads currently required in FMVSS No. 109 but not to the levels proposed by industry in the original GTS-2000 proposal. The RMA now supports a load combination of 85/90/100 percent for P-metric tires, which is identical to the test loads currently required for the endurance test in FMVSS No. 109, but at the higher speeds of 120 km/h, as proposed by the agency. The load combination proposed by RMA for LT tires with load C or D is 75/97/114 percent, and for load range E tires is 70/88/106 percent. The industry's endurance test proposal for P-metric and LT tires is based on a 24-hour test, which represents a 10-hour reduction in the endurance test time from FMVSS No. 109.
c. Inflation pressure
The inflation pressure of 180 kPa represents a 25 percent under-inflation for 240 kPa maximum inflation pressure tires and is the same inflation pressure currently required for the endurance test in FMVSS No. 109. Tires tested to more severe levels of underinflation, e.g., 160 kPa, failed much sooner into the 50-hour endurance test than those tested at 180 kPa.
d. Speed
The proposed test is conducted at 120 km/h (75 mph). The current endurance test in FMVSS 109 is conducted at 80 km/h (50 mph). A 80 km/h test speed may have been an appropriate test speed in 1968 when initially proposed for bias ply tires. However, today, it is too low a speed for evaluating the endurance of today's tires given current vehicle performance capabilities and speed limits. (35) In addition, speed limits on interstate highways across the U.S. have reached as high as 75 mph, with actual vehicle traffic speeds typically at least several miles per hour above the posted speed limit.
e. Duration
NHTSA is proposing a 40-hour test at 120 km/h. The total test distance is 4800 km (3000 miles), which is almost double the distance for the current endurance test in FMVSS No. 109 (1700 miles at 80 km/h). The proposed test duration represents a slight increase from the current 34-hour test in FMVSS No. 109.
3. Low Inflation Pressure Tests
The TREAD Act requires that light vehicles be equipped with a tire pressure monitoring system, effective November 1, 2003, to indicate to the driver when any of the tires on his vehicle is significantly underinflated. NHTSA has proposed to establish 20 psi as a low pressure threshold at or above which the low pressure lamp must be activated. (36)
NHTSA proposes to include in the new light vehicle tire standard a low inflation pressure test to ensure a minimum level of endurance and/or high speed performance/safety when operated at a significant level of under-inflation. To aid the agency in choosing an appropriate test, NHTSA seeks comments on the following alternative tests: 1) the Low Pressure - TPMS test, 2) or the Low Pressure High Speed test. Both proposed tests are described and detail below.
a. Low Pressure - TPMS
The Low Pressure - TPMS test includes a linkage between the proposed requirements of the tire pressure monitoring system standard and the proposed endurance test for the tire standard upgrade proposed requirements. The former test is predicated upon the notion that a low pressure test would be most appropriate on tires that have completed the endurance test because a significantly underinflated condition for a tire is more likely to occur in a tire after several weeks of natural air pressure loss or due to a slow leak. The parameters for this test, which the tire must complete without failure, are as follows:
A tire complies with the proposed requirements if, at the end of the test, there is no visual evidence of tread, sidewall, ply, cord, inner liner, or bead separation, chunking, broken cords, cracking, or open splices, and the tire pressure is not less than the initial test pressure.
As discussed, supra, the agency also conducted a test at 140 kPa (20 psi) inflation pressure, at a speed of 120 km/h (75 mph) for a duration of 90 minutes, on the same tires (2 samples of each of the 12 brands) that successfully completed the endurance test to evaluate tire performance at the low inflation threshold level being proposed for tire pressure monitoring systems for light vehicles. Similar tests were performed using the LT tires, but at low inflation values commensurate with about 58 percent of their maximum inflation pressure. The test results indicated that all 24 tires tested completed the 90-minute low inflation test without failure.
The agency believes that this test provides an extra safeguard to ensure that tires which were able to successfully complete the endurance testing can also complete an additional 90-minute test at low inflation pressures.
b. Low Pressure - High Speed Test
This proposed test provides a linkage between the proposed TPMS requirements and the proposed high speed test. While it would evaluate tires at a lower load than that specified in the Low Pressure -TPMS test, the Low Pressure - High Speed test would ensure that a manufacturer designs a tire so that its high speed performance would comply with the test requirements not only at recommended inflation pressure, but also at a low inflation pressure. The parameters for this test are as follows:
A tire complies with the proposed requirements if, at the end of the test, there is no visual evidence of tread, sidewall, ply, cord, inner liner, or bead separation, chunking, broken cords, cracking, or open splices, and the tire pressure is not less than the initial test pressure.
The above conditions place the test point slightly below the T&RA load curves. The T&RA load curves establish the load capacity a tire is designed to carry at a specific inflation pressure A tire is considered to have passed the test if it completes the 30 minute step at 160 km/h (100 mph).
NHTSA recently conducted testing of the above parameters on 8 tire brands. The results of this testing are contained in a report which has been added to the docket for this rulemaking. The results indicate that 30 percent of tires with an "S" speed rating, 63 percent of tires with an "R" speed rating, and 75 percent of tires with a "Q" speed rating would not pass this test. However, 70 percent of tires with an "S" speed rating, and all "T" and "H" rated tires would have completed the test. The following bullets summarize key conclusions derived from the results:
Effect of test pressure on tire performance - Inflation pressure has a significant effect on speed-at-failure. An inflation pressure of 180 kPa (26 psi) produces a substantial number (32 out of 168, or 19 percent) of failures at speeds less than the rated speed of the tire.
Combined effect of load and pressure on tire performance - The combination of NHTSA and RMA data supports the hypothesis that the performance of a tire is the same for a test condition anywhere on the T&RA load curve except for inflation pressure below 180 kPa (26 psi). At these lower pressures, specifically at 140 kPa (20 psi), failure rates are higher for tires with lower speed ratings than would be predicted from the results of tests run at higher pressures and loads that correspond to points on the T&RA load curve, i.e., the proposed high-speed test condition.
Effect of length of time at a speed on tire performance - For high-speed tests of tires at the maximum sidewall pressure (240 kPa (35 psi) for the tires tested), it may be necessary to test with durations greater than 10 minutes to fully judge failure rates. For tests at lower pressures, the results do not provide a consistent picture. For example, the RMA data at 180 kPa (26 psi) suggests that it probably is not necessary to test for more than 10 durations. However, the NHTSA data at 140 kPa (20 psi) suggests that 10 minutes may not be a sufficiently long duration.
4. Road Hazard Impact Test
The agency proposes that a road hazard impact test replace the strength (plunger) test in the new standard. A tire complies with the proposed requirements if, at the end of the test, there is no visual evidence of tread, sidewall, ply, cord, inner liner, or bead separation, chunking, broken cords, cracking, or open splices, and the tire pressure is not less than the initial test pressure.
A road hazard impact test simulates a tire impacting a road hazard, such as a pothole or curb, and is a more realistic test for radial tires than the current strength test in FMVSS No. 109. For this test, NHTSA is utilizing the existing SAE Recommended Practice J1981, Road Hazard Impact Test for Wheel and Tire Assemblies (Passenger Car, Light Truck, and Multipurpose Vehicles) ("J1981").
J1981 was developed to provide a uniform test procedure for evaluating the effect, on wheel and tire assemblies, of impacting a road hazard such as a pothole or curb. J1981 does not attempt to simulate the exact conditions encountered when the wheel and tire assembly strikes such a hazard. The equipment developed for this test does, however, attempt to reproduce under controlled conditions the wheel and tire deformations that may be experienced with a road hazard impact. The test equipment can also be used to determine, with a high degree of accuracy, the threshold condition at which tire damage first occurs.
In the preparation of J1981, laboratory and road tests carried out by a number of manufacturers were studied. The pendulum test specified in J1981 was designed to provide equivalent damage with low cost equipment that would give accurate and reproducible results. The test is designed for testing of wheel and tire assemblies used with passenger cars, light trucks, and multipurpose vehicles. The test is limited to a front (radial) impact with both wheel rim flanges being impacted simultaneously.
The following bullets summarize the key components of a Road Hazard Impact Test Machine (used by STL) and the test procedure for the Road Hazard Impact Test as specified by SAE J1981:
The basic machine consists of a framework designed to guide the Pendulum Weight System so that, when released, it will free fall and impact the wheel tire assembly. The wheel/tire assembly is adjustable so that it can be aligned with the Pendulum Weight Assembly.
The equipment must be calibrated to ensure that the impact force is correct since the impact force on the wheel and tire assembly depends on the length of the pendulum, the shape of the striker, and the friction at the fulcrum.
The tire and wheel assembly, inflated to the required test pressure, is installed on the test fixture. The inflation pressure proposed for P-metric tires is 180 kPa, and for LT tires load ranges C, D, and E, it is 260 kPa, 340 kPa, and 410 kPa, respectively.
The 54 kg striker is raised to the predetermined drop height based on the pendulum centerline angle of 80 degrees to the vertical. The striker is allowed to fall freely from this predetermined height to impact the test tire and wheel assembly.
The test is repeated for a total of five equally spaced points around the circumference of the tire.
The tire pressure at the end of the test shall not be less than the initial test pressure, and there must be no visual evidence of tire failure.
5. Bead Unseating
The current resistance-to-bead unseating test is designed to evaluate how well the tire bead remains on the rim during turning maneuvers. The test forces currently used in FMVSS No. 109 are based on bias ply tires and are typically not stringent enough for radial tires. For this reason, the industry, in GTS-2000, recommended that the test be deleted from the standard because radial tires are able to satisfy the test easily. Results from the agency's 1997-1998 dynamic rollover testing, however, provide a strong rationale for seeking to upgrade, rather than delete, the bead unseating requirement in FMVSS No. 109. In this NHTSA test program, vehicles experienced bead unseating on three of twelve test vehicles. This bead unseating occurred during severe maneuvers, but on level surfaces without any external impact to the tire. Such bead unseating in the real world would pose serious safety concerns. Therefore, NHTSA proposes to replace the current bead unseating test in FMVSS No. 109 with the Toyota Air Loss Test.
The Toyota Air Loss Test was developed by Toyota to evaluate tubeless tire performance. While the current FMVSS No. 109 bead unseating test applies force in the middle of the sidewall, the Toyota Air Loss Test applies force at the tire tread surface edge. The tire tread surface edge is the actual location at which force occurs due to tire/road interface during severe vehicle maneuvers. There are two general methods for conducting the Toyota test:
1. Air Loss Bench Test Method: A tire that receives a lateral force from the ground is deformed and may be deflated as its tire bead is separated from the rim bead. The air loss test is intended to measure the tire inflation pressure at which a tire is deflated under the above condition. The test may be conducted with an actual vehicle or with a tire assembly on a test bench.
2. On-Vehicle Air Loss Test Method: When an actual vehicle is used for the