TRB SPECIAL REPORT 286

Tires and Passenger Vehicle Fuel Economy

Informing Consumers, Improving Performance

Committee for the National Tire Efficiency Study

Transportation Research Board

Board on Energy and Environmental Systems

NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES

Transportation Research Board

Washington, D.C.

2006

www.TRB.org



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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 TRB SPECIAL REPORT 286 Tires and Passenger Vehicle Fuel Economy Informing Consumers, Improving Performance Committee for the National Tire Efficiency Study Transportation Research Board Board on Energy and Environmental Systems NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES Transportation Research Board Washington, D.C. 2006 www.TRB.org

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Transportation Research Board Special Report 286 Subscriber Category IB energy and environment Transportation Research Board publications are available by ordering individual publications directly from the TRB Business Office, through the Internet at www.TRB.org or national-academies.org/trb, or by annual subscription through organizational or individual affiliation with TRB. Affiliates and library subscribers are eligible for substantial discounts. For further information, contact the Transportation Research Board Business Office, 500 Fifth Street, NW, Washington, DC 20001 (telephone 202-334-3213; fax ; or e-mail TRBsales@nas.edu). Copyright 2006 by the National Academy of Sciences. All rights reserved. Printed in the United States of America. NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to the procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. This report was sponsored by the National Highway Traffic Safety Administration of the U.S. Department of Transportation. Library of Congress Cataloging-in-Publication Data Tires and passenger vehicle fuel economy : informing consumers, improving performance / Committee for the National Tire Efficiency Study, Transportation Research Board of the National Academies. p. cm.—(Special report / Transportation Research Board of the National Academies ; 286) ISBN 0-309-09421-6 1. Transportation, Automotive—United States. 2. Automobiles—Tires. 3. Automobiles—Fuel consumption. 4. Consumer education—United States. I. National Research Council (U.S.). Transportation Research Board. Committee for the National Tire Efficiency Study. II. Special report (National Research Council (U.S.). Transportation Research Board) ; 286. HE5623.T57 2006 629.2′482—dc22 2006044478

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both the Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. William A. Wulf are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is a division of the National Research Council, which serves the National Academy of Sciences and the National Academy of Engineering. The Board’s mission is to promote innovation and progress in transportation through research. In an objective and interdisciplinary setting, the Board facilitates the sharing of information on transportation practice and policy by researchers and practitioners; stimulates research and offers research management services that promote technical excellence; provides expert advice on transportation policy and programs; and disseminates research results broadly and encourages their implementation. The Board’s varied activities annually engage more than 5,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Transportation Research Board 2006 Executive Committee* Chair: Michael D. Meyer, Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta Vice Chair: Linda S. Watson, Executive Director, LYNX–Central Florida Regional Transportation Authority, Orlando Executive Director: Robert E. Skinner, Jr., Transportation Research Board Michael W. Behrens, Executive Director, Texas Department of Transportation, Austin Allen D. Biehler, Secretary, Pennsylvania Department of Transportation, Harrisburg John D. Bowe, Regional President, APL Americas, Oakland, California Larry L. Brown, Sr., Executive Director, Mississippi Department of Transportation, Jackson Deborah H. Butler, Vice President, Customer Service, Norfolk Southern Corporation and Subsidiaries, Atlanta, Georgia Anne P. Canby, President, Surface Transportation Policy Project, Washington, D.C. Douglas G. Duncan, President and CEO, FedEx Freight, Memphis, Tennessee Nicholas J. Garber, Henry L. Kinnier Professor, Department of Civil Engineering, University of Virginia, Charlottesville Angela Gittens, Vice President, Airport Business Services, HNTB Corporation, Miami, Florida Genevieve Giuliano, Professor and Senior Associate Dean of Research and Technology, School of Policy, Planning, and Development, and Director, METRANS National Center for Metropolitan Transportation Research, University of Southern California, Los Angeles (Past Chair, 2003) Susan Hanson, Landry University Professor of Geography, Graduate School of Geography, Clark University, Worcester, Massachusetts James R. Hertwig, President, CSX Intermodal, Jacksonville, Florida Gloria J. Jeff, General Manager, City of Los Angeles Department of Transportation, California Adib K. Kanafani, Cahill Professor of Civil Engineering, University of California, Berkeley Harold E. Linnenkohl, Commissioner, Georgia Department of Transportation, Atlanta Sue McNeil, Professor, Department of Civil and Environmental Engineering, University of Delaware, Newark Debra L. Miller, Secretary, Kansas Department of Transportation, Topeka Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington Carol A. Murray, Commissioner, New Hampshire Department of Transportation, Concord John R. Njord, Executive Director, Utah Department of Transportation, Salt Lake City (Past Chair, 2005) Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson * Membership as of May 2006.

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Henry Gerard Schwartz, Jr., Senior Professor, Washington University, St. Louis, Missouri Michael S. Townes, President and CEO, Hampton Roads Transit, Virginia (Past Chair, 2004) C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin Marion C. Blakey, Administrator, Federal Aviation Administration, U.S. Department of Transportation (ex officio) Joseph H. Boardman, Administrator, Federal Railroad Administration, U.S. Department of Transportation (ex officio) Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, Georgia (ex officio) George Bugliarello, Chancellor, Polytechnic University of New York, Brooklyn; Foreign Secretary, National Academy of Engineering, Washington, D.C. (ex officio) Sandra K. Bushue, Deputy Administrator, Federal Transit Administration, U.S. Department of Transportation (ex officio) J. Richard Capka, Acting Administrator, Federal Highway Administration, U.S. Department of Transportation (ex officio) Thomas H. Collins (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, Washington, D.C. (ex officio) James J. Eberhardt, Chief Scientist, Office of FreedomCAR and Vehicle Technologies, U.S. Department of Energy (ex officio) Jacqueline Glassman, Deputy Administrator, National Highway Traffic Safety Administration, U.S. Department of Transportation (ex officio) Edward R. Hamberger, President and CEO, Association of American Railroads, Washington, D.C. (ex officio) Warren E. Hoemann, Deputy Administrator, Federal Motor Carrier Safety Administration, U.S. Department of Transportation (ex officio) John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, D.C. (ex officio) John E. Jamian, Acting Administrator, Maritime Administration, U.S. Department of Transportation (ex officio) J. Edward Johnson, Director, Applied Science Directorate, National Aeronautics and Space Administration, John C. Stennis Space Center, Mississippi (ex officio) Ashok G. Kaveeshwar, Administrator, Research and Innovative Technology Administration, U.S. Department of Transportation (ex officio) Brigham McCown, Deputy Administrator, Pipeline and Hazardous Materials Safety Administration, U.S. Department of Transportation (ex officio) William W. Millar, President, American Public Transportation Association, Washington, D.C. (ex officio) (Past Chair, 1992) Suzanne Rudzinski, Director, Transportation and Regional Programs, U.S. Environmental Protection Agency (ex officio) Jeffrey N. Shane, Under Secretary for Policy, U.S. Department of Transportation (ex officio) Carl A. Strock (Maj. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, D.C. (ex officio)

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Board on Energy and Environmental Systems Douglas M. Chapin, MPR Associates, Inc., Alexandria, Virginia, Chair Robert W. Fri, Resources for the Future (senior fellow emeritus), Washington, D.C., Vice Chair Allen J. Bard, University of Texas, Austin David L. Bodde, Clemson University, South Carolina Philip R. Clark, GPU Nuclear Corporation (retired), Boonton, New Jersey E. Linn Draper, Jr., American Electric Power, Inc. (emeritus), Austin, Texas Charles Goodman, Southern Company, Birmingham, Alabama David G. Hawkins, Natural Resources Defense Council, Washington, D.C. Martha A. Krebs, California Energy Commission, Sacramento Gerald L. Kulcinski, University of Wisconsin, Madison David K. Owens, Edison Electric Institute, Washington, D.C. William F. Powers, Ford Motor Company (retired), Ann Arbor, Michigan Tony Prophet, Carrier Corporation, Farmington, Connecticut Michael P. Ramage, ExxonMobil Research & Engineering Company (retired), Moorestown, New Jersey Edward S. Rubin, Carnegie Mellon University, Pittsburgh, Pennsylvania Maxine Savitz, Honeywell, Inc. (retired), Los Angeles, California Philip R. Sharp, Harvard University, Cambridge, Massachusetts Scott W. Tinker, University of Texas, Austin

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Committee for the National Tire Efficiency Study Dale F. Stein, Michigan Technological University (retired), Tucson, Arizona, Chair James E. Bernard, Iowa State University, Ames John Eagleburger, Goodyear Tire Company (retired), North Canton, Ohio Richard J. Farris, University of Massachusetts, Amherst David Friedman, Union of Concerned Scientists, Washington, D.C. Patricia S. Hu, Oak Ridge National Laboratory, Knoxville, Tennessee Wolfgang G. Knauss, California Institute of Technology, Pasadena Christopher L. Magee, Massachusetts Institute of Technology, Cambridge Marion G. Pottinger, M’gineering, LLC, Akron, Ohio Karl J. Springer, Southwest Research Institute (retired), San Antonio, Texas Margaret A. Walls, Resources for the Future, Washington, D.C. Joseph D. Walter, University of Akron, Ohio Project Staff Thomas R. Menzies, Jr., Study Director, James Zucchetto, Division on Engineering and Physical Sciences

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Preface In February 2005, in response to a congressional request1 and with funding from the National Highway Traffic Safety Administration (NHTSA) of the U.S. Department of Transportation, the National Research Council (NRC) formed the Committee for the National Tire Efficiency Study. The committee consisted of 12 members with expertise in tire engineering and manufacturing, mechanical and materials engineering, and statistics and economics. The committee was given the following charge: This study will develop and perform a national tire efficiency study and literature review to: Consider the relationship that low rolling resistance replacement tires designed for use on passenger cars and light trucks have on fuel consumption and tire wear life; Address the potential for securing technically feasible and cost-effective replacement tires that do not adversely affect safety, including the impacts on performance and durability, or adversely impact tire tread life and scrap tire disposal; Fully consider the average American “drive cycle” in its analysis; Address the cost to the consumer including the additional cost of replacement tires and any potential fuel savings. In approaching its charge, the committee made a number of decisions affecting the study scope and logic and content of the report. 1 Conference Report 108-401, to Accompany H.R. 2673, Making Appropriations for Agriculture, Rural Development, Food and Drug Administration, and Related Agencies for the Fiscal Year Ending September 30, 2004, and for Other Purposes. November 25, 2003, p. 971.

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 These decisions are explained in Chapter 1. For the most part, the committee sought to answer each of the questions asked by Congress by examining the technical literature and available data on passenger tire performance characteristics. The committee met four times between April and October 2005 and communicated extensively by e-mail and teleconference. Meetings included open sessions for gathering information from outside experts from industry, government, and academia, as well as closed deliberative sessions for discussions among committee members. In addition, selected committee members, staff, and consultants met with representatives of automobile manufacturers and experts in tire materials and technologies between committee meetings. Before the committee’s final meeting, several tire manufacturers, acting through the Rubber Manufacturers Association, made available measurements of the rolling resistance of a sample of more than 150 new replacement passenger tires as well as some original equipment (OE) tires. Although the sample was not scientifically derived, the data proved helpful to the committee as it sought to answer the various questions in the study charge. The timing of the data’s availability late in the study process limited the statistical analyses that could be undertaken by the committee. Nevertheless, the committee appreciates the efforts of Michelin North America, Bridgestone Americas, and the Goodyear Tire and Rubber Company in providing these data as requested. ACKNOWLEDGMENTS During the course of its deliberations, the committee benefited from presentations and information provided by the following individuals, whom the committee acknowledges and thanks: Ronald Medford, Joseph Kanianthra, and W. Riley Garrott, NHTSA; Lois Platte, U.S. Environmental Protection Agency; Luke Tonachel, National Resources Defense Council; Donald Shea, Tracey Norberg, and Michael Blumenthal, Rubber Manufacturers Association; Arnold Ward, California Energy Commission; Christopher Calwell, Ecos Consulting, Inc.; Ed Cohn, California Tire Dealers Association—South; Mitchell Delmage, California Integrated Waste Management Board; Andrew Burke, Daniel Sperling, Paul Erickson, Andrew Frank, and Christopher Yang, Institute of

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Transportation Studies, University of California, Davis; Terry Laveille, California Tire Report; Donald Amos, Continental Tire North America; Anthony Brinkman, Cooper Tire and Rubber Company; Georg Böhm (retired) and Dennis Candido, Bridgestone Americas; Simeon Ford, Goodyear Tire and Rubber Company; Michael Wischhusen, Michelin North America; Paul Daniels, Pirelli Tire North America; and Alan McNeish, Degussa (retired). The committee is grateful to Jonathan Mueller and James MacIsaac of NHTSA for serving as the agency’s technical liaisons to the study. Special thanks go to Daniel Sperling, Andrew Burk, Alexis Palecek, and other staff, faculty, and students of the Institute of Transportation Studies at the University of California, Davis, which hosted the committee’s second meeting. Thanks also go to Guy Edington, Director of the Kumho Tire Technical Center, which hosted a subcommittee meeting in Akron, Ohio, and to Douglas Domeck, James Popio, James McIntyre, and other staff of Smithers Scientific Service, Inc., which provided a tour of the company’s Transportation Test Center in Ravenna, Ohio. In addition, the committee is grateful to Ed Noga of Rubber and Plastics News, which provided Internet access to its archives, and to John Smith of Standard Testing Laboratories for providing tire section cutaways and other presentation aids. Thomas R. Menzies, Jr., managed the study and drafted the final report under the guidance of the committee and the supervision of Stephen R. Godwin, Director of Studies and Information Services. Committee member Marion G. Pottinger drafted the Appendix, and committee member Margaret A. Walls conducted the multiple regression analyses in Chapters 3 and 4. The committee was aided by consultant K. G. Duleep of Energy and Environmental Analysis, Inc. He interviewed automobile manufacturers to learn about their interest in the rolling resistance characteristics of OE tires. He also provided the committee with analyses of the influence of passenger tires on motor vehicle fuel economy. The report was reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise in accordance with procedures approved by the NRC’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. The committee thanks the following individuals for their review of this report: Karin M. Bauer, Midwest Research Institute, Kansas City, Missouri; Nissim Calderon, the Goodyear Tire and Rubber Company (retired), Boca Raton, Florida; W. Dale Compton, Purdue University, West Lafayette, Indiana; Alan N. Gent, University of Akron, Ohio; Thomas D. Gillespie, University of Michigan Transportation Research Institute, Ann Arbor; Marc H. Ross, University of Michigan (Emeritus), Ann Arbor; Nicholas M. Trivisonno, B. F. Goodrich (retired), Broadview Heights, Ohio; and Sarah E. West, Macalester College, St. Paul, Minnesota. Although these reviewers provided many constructive comments and suggestions, they were not asked to endorse the committee’s findings and conclusions, nor did they see the final report before its release. The review of this report was overseen by Maxine L. Savitz, Honeywell International, Inc. (retired), and C. Michael Walton, University of Texas at Austin. Appointed by NRC, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution. Suzanne Schneider, Associate Executive Director of the Transportation Research Board, managed the report review process. The report was edited and prepared for publication by Norman Solomon, Senior Editor, and the final manuscript was formatted and prepared for initial release and web posting by Jennifer J. Weeks, under the supervision of Javy Awan, Director of Publications. Special thanks go to Frances Holland and Amelia Mathis for assistance with meeting arrangements and correspondence with the committee.

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Abbreviations and Glossary Aspect ratio. A tire’s section height divided by its section width, multiplied by 100. Aspect ratio is listed in the size designation on the passenger tire sidewall. Typical tire aspect ratios range from 35 for tires used on sports cars to 75 for tires used on utility-type vehicles. Bead. A ring of steel wire that anchors the tire carcass plies to the rim. Belt. An assembly of plies extending from shoulder to shoulder of a tire and providing a reinforcing foundation for the tread. In radial-ply tires, the belts are typically reinforced with fine steel wire having high tensile strength. Bias-ply tire. A pneumatic tire in which the ply cords that extend to the beads are laid at alternate angles substantially less than 90 degrees to the centerline of the tread. The bias-ply tire was the predominant passenger tire in the United States before 1980 but is no longer in common use; it has been supplanted by the radial-ply tire. Carbon black. A very fine, nano-size particulate carbon used as a reinforcing filler in rubber compounds to provide abrasion resistance and other favorable properties. Carcass or casing. The tire structure, except tread and sidewall rubber, that bears the load when the tire is inflated. Coastdown. A process in which a vehicle or test machine is allowed to slow down freely from a high to a low speed without application of external power or braking.

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Coefficient of friction. The ratio of friction force to normal force to cause sliding expressed as a unitless value (i.e., friction force generated between tire tread rubber and the road surface divided by vertical load). Corporate average fuel economy (CAFE). A federal program that sets a minimum performance requirement for passenger vehicle fuel economy. Each automobile manufacturer must achieve an average level of fuel economy for all specified vehicles manufactured in a given model year. The National Highway Traffic Safety Administration administers the CAFE program. The U.S. Environmental Protection Agency develops the vehicle fuel economy test procedures. EPA. U.S. Environmental Protection Agency. EPA is responsible for developing the federal test procedures for measuring and rating the fuel economy of new passenger cars and light trucks. The federal test procedures are used for new vehicle fuel economy labeling and the corporate average fuel economy program. FMVSS. Federal Motor Vehicle Safety Standards. The FMVSS include regulations governing passenger tire safety. High-performance tire. A passenger tire designed for the highest speed and handling, generally having the speed symbol W, Y, or Z in the United States. Hysteresis. A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance and is attributed to the viscoelastic characteristics of the rubber. Light truck (LT) tire. A tire constructed for heavy loads and rough terrain that is usually used on medium-duty trucks in commercial service. These tires contain the prefix LT before the metric size designation

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 molded on the tire sidewall and are inflated to higher pressures than are normal passenger tires. LT tires are not regulated as passenger tires and are therefore not examined in this study. NHTSA. National Highway Traffic Safety Administration. Among its responsibilities, NHTSA administers the Federal Motor Vehicle Safety Standards, the Uniform Tire Quality Grading system, and the corporate average fuel economy program. Original equipment manufacturer (OEM). An automobile manufacturer. Original equipment (OE) passenger tire. A tire that is provided as original equipment on new passenger vehicles. Such tires are often designed for particular vehicles to the specifications of the automobile manufacturer. Passenger tire. A tire constructed and approved for use on passenger vehicles and that usually contains the prefix P before the metric size designation on the tire sidewall. Federal Motor Vehicle Safety Standards and Uniform Tire Quality Grading standards are established specifically for passenger tires. Passenger vehicle. For the purposes of this report, a car or light truck used primarily for passenger transportation. Most of these vehicles use passenger tires. Most vans, pickup trucks, and sport utility vehicles that are categorized as light trucks by the federal government are considered passenger vehicles. Light trucks that exceed 6,000 pounds in gross vehicle weight are usually used for nonpassenger commercial service. They are usually equipped with light truck (LT) tires. Performance tire. A passenger tire intended to provide superior handling and higher speed capabilities and generally having a speed symbol of H or V in the United States. Ply. A sheet of rubber-coated parallel tire cords. Tire body plies are layered.

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Radial-ply construction. A pneumatic tire construction under which the ply cords that extend to the beads are laid at approximately 90 degrees to the centerline of the tread. Two or more plies of reinforced belts are applied, encircling the tire under the tread. Radial-ply tires were introduced in Europe during the 1950s and came into common use in the United States during the 1970s. Reinforcing filler. Material added to rubber compounds to provide favorable properties, including resistance to abrasion. The two most common reinforcing fillers are carbon black and silica. Replacement passenger tire. A tire purchased in the aftermarket to replace an original equipment tire. Rim diameter. The diameter of a wheel measured at the intersection of the bead seat and the flange. The rim diameter is listed in the size designation on the passenger tire sidewall. Common rim diameters for passenger tires range from 13 to 20 inches. RMA. Rubber Manufacturers Association. RMA is the national trade association for the rubber products industry in the United States. Most domestic and foreign tire makers who produce tires in the United States are members of the association. Rolling resistance. The force at the axle in the direction of travel required to make a loaded tire roll. Rolling resistance coefficient (RRC). The value of the rolling resistance force divided by the wheel load. The Society of Automotive Engineers (SAE) has developed test practices to measure the RRC of tires. These tests (SAE J1269 and SAE J2452) are usually performed on new tires. When measured by using these standard test practices, most new passenger tires have reported RRCs ranging from 0.007 to 0.014. Run-flat tire. A type of pneumatic tire constructed of special materials, supports, and configurations that allow it to travel for a limited distance

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 and speed after experiencing a loss of most or all inflation pressure. While these tires usually have greater weight and resultant rolling resistance, they permit the elimination of storage space and weight associated with a spare tire and jack. SAE. Society of Automotive Engineers. SAE technical committees have developed standardized test practices for measuring the rolling resistance of tires. SAE J1269. A recommended practice of SAE that defines a standardized method for testing tire rolling resistance under steady-state conditions at 80 km/h (50 mph). SAE J2452. A recommended practice of SAE that defines a standardized method for testing tire rolling resistance in simulation of a coastdown from 120 to 15 km/h. Section height. The linear distance between an inflated unloaded tire’s overall (outside) tread diameter and the intersection of the bead seat and the flange. Section width. The linear distance between the outside sidewalls of an inflated unloaded tire (not including decorations such as lettering) when mounted on the measuring rim. Treads are always narrower than the section width. Sidewall. The portion of the tire between the bead and the tread. The tire’s name, safety codes, and size designation are molded on the sidewall. Silane. An organo-silicate compound that is sometimes mixed with silica to promote dispersion and bonding. Silica. A very fine, nano-size particle, silicon dioxide, used as a reinforcing filler in rubber compounding. Speed rating. A letter assigned to a tire denoting the maximum speed for which the use of the tire is rated (e.g., S = 112 mph, H = 130 mph).

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 The speed rating is contained in the tire size designation molded on the sidewall. Tire pressure monitoring system (TPMS). A warning system in motor vehicles that indicates to the operator when a tire is significantly under-inflated. Some systems use sensors in the tire to transmit pressure information to a receiver. Some do not have pressure sensors but rely on wheel speed sensors to detect and compare differences in wheel rotational speeds, which can be correlated to differences in tire pressure. Traction. The ability of a loaded tire to generate vehicle control forces through frictional interaction with a road surface. Tread. The peripheral portion of the tire designed to contact the road surface. The tread band consists of a pattern of protruding ribs and grooved channels on top of a base. Tread depth is measured on the basis of groove depth. Traction is provided by the tread. Tread compound. The general term that refers to the chemical formula of the tread material. The compound consists of polymers, reinforcing fillers, and other additives that aid in processing and slow degradations from heat, oxygen, moisture, and ozone. Tread wear life. Total miles traveled by a tire until its tread wears out, which is usually defined as a remaining groove depth of 2/32 inch for a passenger car tire that exhibits even wear. Uniform Tire Quality Grade (UTQG). A passenger tire rating system that grades a tire’s performance in tread wear durability, traction, and temperature resistance. UTQG ratings are required by the federal government for most types of passenger tires and are molded on the tire’s sidewall. The tread wear grade is a numeric rating, with a higher number suggesting longer tread wear capability. Most tires receive grades between 100 and 800. The traction grade is assigned on the basis of results of skid tests on wet pavements. Tires are graded AA, A, B, or C, with AA indicating superior wet traction. The temperature grade is assigned to

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 tires tested at various speeds to determine the ability of a tire to dissipate heat. Tires are graded A, B, or C, with A indicating an ability to dissipate heat at higher speeds. USDOT. U.S. Department of Transportation. The National Highway Traffic Safety Administration is an agency of USDOT. Vehicle fuel economy. The average number of miles a vehicle travels per gallon of motor fuel (typically gasoline or diesel fuel). Viscoelastic. A viscoelastic material is characterized by possessing both viscous and elastic behavior. A purely elastic material is one in which all energy stored in the material during loading is returned when the load is removed. In contrast, a purely viscous material stores no strain energy, and all of the energy required to deform the material is simultaneously converted into heat. Some of the energy stored in a viscoelastic system is recovered on removal of the load, and the remainder is dissipated as heat. Rubber is a viscoelastic material. Wear resistance. Resistance of the tread to abrasion from use on a normal road surface. Wet traction. The ability of a loaded tire to generate vehicle control forces through frictional interaction with a wet road surface.

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 Contents     Executive Summary   1 1   Introduction   9      Study Charge and Scope   10      Policy Context   11      Study Approach and Information Base   13      Report Organization   16 2   Background on Passenger Tires   17      Tire Terminology and Trends   17      History of Tire Development   20      Tire Industry Structure   26      Tire Safety and Consumer Information Standards   29      Summary   33 3   The Tire’s Influence on Passenger Vehicle Fuel Consumption   36      Recent History of Interest in Vehicle Fuel Economy   37      Examining the Influence of Tires on Vehicle Fuel Economy   39      Factors Causing and Influencing Rolling Resistance   42      Measuring and Expressing Rolling Resistance   47      Rolling Resistance and Fuel Economy   49      Rolling Resistance Data for Passenger Tires   51      Summary   73

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Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance - TRB Special Report 286 4   Rolling Resistance, Traction, and Wear Performance of Passenger Tires   77      Effects on Traction and Safety Performance   79      Effects on Tread Life and Scrap Tires   88      Summary   102 5   National Consumer Savings and Costs   105      Consumer Fuel Savings   107      Consumer Tire Expenditures   108      Overall Effect on Consumer Expenditures   119 6   Findings, Conclusions, and Recommendations   123      Key Findings and Estimates   124      Conclusions in Response to Study Charge   131      Recommendations to Inform Consumers   134     APPENDIX: Explanation and Comparison of Society of Automotive Engineers Test Procedures for Rolling Resistance   137     Study Committee Biographical Information   146