DOT HS-801 440 122 uzq ' 4 -. EHICLE-IN-USE LIMIT PEFORMANCE Pro-zflTig Ww ,5(ll"E - ;:-2 rc ". z s-g MOa".ND TIRE FACTORS. * ILK??!a?? :VIE IN USE. ;I Contract No. DOT-HS-031-3-693 March 1975 Final Report PREPARED FOR: U.S. DEPARTMENT OF TRANSPORTATION NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION WASHINGTON, D.C. 20590 Document is available to the public through the National Technical Information Service, Springfield, Virginia 22151 ,?his document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Govern- ment assumes no liability for its contents or use thereof. --, .. .- -..A-1- ----- + -.__.. - . i 1, i~r;.~~~:..-. I 1 I DOT-HS - 801-440 I I I--- ttle on? S~bl~tie Vehicle- In-Use Liniit I'el.formance and Tire Factors T& -Tir~in.Use -.------- -- --- - -- 1---.----- 8 f'erfortn~n~O~gontxottorl R.l'orf No 7 Avth0.l~) James E. Bernard? Paul S. Fancher, Rajiv Gupt;] i1 Hovard ibloncarz, Leonard Segel ml-HSRI-PF-75-1-2 10 Work Un~t140 ng Urson rct~snKurne anc Address Safety !:csee~-ch Ins ti tute The Uni versity of Jlichigan 11. Contract or Cront NO. ~HuronParkliay 6 Baxtcr Road DOT-HS-031-3-693 (AR~?.rbor, ?fic]lj gcin 48105 13. Type 01 Report ond Pertoo Covered -.--- - 12 S;,r .or ng Aaency Nome and Addre's Appendix A, B, C i--IXztlonal High~iayTraffic Safety Administration 6/73 - 2/75 !I!. 5. D~partmentof Transportation Kssn.7. ngton, 3. C. 20590 14. Sponsoring Agcncy Code 16 Absfrucl The influence of tire-in-use factors (inflation pressure, replacement mixes, and wear) on the steering and braking respoilse of autc~~!obiltsjs examined through analysis, simulation, laboratory and j over-the-yoad tire testing, and vehicle testing. Results for a 1971. I !.lustang 2nd a 1973 Buick station wagon illustrate the influence of 1 tire-in-use factors on (a) the open-loop braking and/or turning pcr- formance in drastic maneuvers on wet and dry surfaces, and (b) the I understcer/oversteer factor for maneuvers involving lateral acceleratio belors 0.3 g. This investigation shows that differences in tire mechanical pro- perties betweer the front and rear wheels (as caused by tire-in-use f acto?.~j can cause significant and potentially dangerous changes in I. I klni: les2onse and from the stability and control characteristics bntended by the vehicle manufacturer. The report recommends that (1) inspection limits for inflation pressure be within +1 psi of the man, acturerfs reconnended level, (2) minimum tread-groove depth exceed /32", and (3) further research be conducted to develop a cost- I ffective means for indicating the lateral force characteristics of itire. ---- 17. Key Words 19. D~strtbvt~onStatement Tire shear force, vehicle / Document is available to the public 1 echani cs . tjrc ear , tire inflatioa through the National Technical Infomaticn ressure , replace~~nntti re mixes, >rnergellcy rrancul.ers , l incar analys ifI Service, Springfield , Virginia 22151 1-f dl rectional rcsponsc, vehicle si~wlation. -- -- 21. No. of Pager 22. Pf~ce 19. Sccur~tyCloss~f. !ol ?,IS rcporl) 20. Secvrttu C!ors~f.(of th~s~o~t) 259 Unclassifj ed 1 ~~~~~~~~~~~d---- -- --- -- L 1 Form DCT F 1700.7 (3.691 n i . r ; i I . .I r i I 1 3-.. --L... - '. 19 TABLE OF CONTENTS APPENDIX A - LITERATURE SURVEY. .......... 1 APPENDIX B - TIRE-VEHICLE SYSTEM SIMULATIONMODEL ............. 72 APPENDIX C - VEHICLE LINEAR ANALYSIS PROGRAM. ..,.. 211 iii APPENDIX A LITERATURE SURVEY Howard Moncarz Al. INTRODUCTION The purpose of this literature survey is to gather, organize, and summarize information relative to the influence of tire- in-use factors on vehicle performance. The tire-in-use factors considered in this survey are: (1) the performance characteristics of different replacement tires, (2) tread wear (both uniform and shoulder wear), (3) inflation pressure, (4) vertical loading, (5) tire temperature, and (6) vehicle speed. Additionally, the interaction between circumferential and lateral force, as well as the effect of wet surfaces on tire performance characteristics, are considered. A sea~chwas undertaken to find those papers that present experimental results and conclusions concerning: (1) the effect of tire-in-use factors on the mechanical properties of pneumatic tires, (2) the effect of tire-in-use factors on vehicle dynamics, and (3) the generation of accelerated wear to simulate actual tire wear. The search was also extended to those papers presenting theories on tire mechanics considered relevant to the project. The manner in which people actually use and maintain their tires serves as a good introduction to the study of tire-in-use factors. Harvey and Brenner [54]* did such a study relying on two surveys-one aimed at obtaining data of the condition of tires from an unbiased sample of passenger car tires in normal use and the second one aimed at obtaining similar data for passenger car tires used mainly in long distance traveling. The tire-in-use factors they examined were tread depth and wear pattern, wheel loading, inflation pressure, tire mix (in regard to using tires of different inflation pressures and/or tread wear), and the effects of temperature. Additionally, they correlated these tire-in-use factors and traffic accidents based on previously published accident data. Highlights quoted from the report are: *Numbers in brackets designate references in the Annotated Bibliography at end of text. 1 "--.A greater percentage of severely worn tires were found on vehicles in accidents than in the general tire population. --Vehicles in accidents have a larger number of severely worn tires on their rear axles than on the front suggesting that it is safer to have newer or less worn tires on the rear axle. --There is a considerable body of evidence indicating that the risk of tire disablement and of loss of vehicle control rises sharply for tires having less than about 2/32-inch of tread depth remaining. --Air towers at service stations are generally not accurate. A motorist relying on a tower gage will have only about a 20 percent change of getting within + 1 psi of the inflation pressure he wants. A single point calibration of the tower gage could decrease the error substantially. --More than one out of four cars has at least one seriously underinflated tire (4 psi or more below the recommended normal inflation pressure for the vehicle) . --About 2 percent of cars are overloaded by 10 percent or more; about 6 percent are overloaded to some extent. Most overloading occurs on station wagons and light trucks, and on passenger cars during vacation trips. --On the average most cars are loaded to about. 80 percent of their allowable load (at the existing equivalent cold tire inflation pressure) ." A2. REPLACEMENT TIRES There are numerous design variables that go into the making of a tire, and each one can have an effect on the per- formance characteristics of the tire [115]. The tire carcass is made of a woven fabric of cords, set at a specified angle to the plane of the tire. The cords may be made from a number of materials. Additionally, rigid breakers, or belts, are attached on a layer of cords and these belts have been made from a variety of materials as well. There are several different types of rubber compounds that are used on the same tire-one type for the tread, another for the sidewalls, a third for the inner lining, etc. Each rubber compound is made from a variety of substances in different ratios to each other to give it the desired properties the designer intends. And of course, tread designs are numerous. With all these design variables there are still others lzhich are important in the actual manufacture of the tire. The same materials put together in different sequences, or treated for different time spans, heated to different temperatures, etc., can produce quite different tires. A2.1 MANUFACTURER Because of the complexity of a tire, no two tire manu- facturers can be said to make any tire in exactly the same way. Thus, in a technical sense it is inappropriate to study the performance differences of the same type of tires made by different manufacturers, because, in fact, the tires are not the same. However, in the marketplace, the consumer has only limited information concerning the design variables of a tire, including the size, the aspect ratio, the general construction, the tread pattern. These variables (with price, of course) will determine which tires a consumer will buy as replacement tires. Thus it is reasonable (in a practical sense) to study manufacturers as a tire-in-use factor, keeping the design variables just mentioned fixed. It should be noted that production by a single manufacturer of several batches of a specified tire may still result in tires being made having significantly different performance characteristics among them. This is due to variables encountered in the actual manufacture of the tire. These variables could vary from day to day, from plant to plant, or possibly even in the same batch of tires manufactured at the same place at the same time. Several investigators have dealt with manufacturer as a variable in determining performance characteristics of tires. They have not made specific conclusions, except to say that there exist substantial differences in performance characteristics between tires of the same size and construction type but different manufacturers [32, 66, 95, 1141. A2.2 DESIGN VARIABLES A literature survey by Schuring, et al. [112], investigated the influence of (1) tire construction type, (2) tread geometry, (3) tread compound, (4) road wheel dimensions, (5) tire aspect ratio, and (6) cord material of OE tires on vehicle performance.