55 YEARS OF RADIALIZATION Jacques Bajer Tire Systems Engineering, Inc. Paper 23 ITEC 2004 Paper 23 Reprint only with permission of Rubber & Plastics News, published by Crain Communications, Inc. T1~E SYSTEMS ENGJNEER1NG, iNC. 16825 Kercheval Ave. Grosse Pointe, M! 48230, U.S.A. Phone: 313/886-6860 Fax: 313/882-3173 Consultants and Designers in Road Tire Vehicle Systems Technology Raw Edge V-Belt and Radial Ply Tire Technology and Manufacturing Systems PRESENTED AT THE INTERNATIONAL TIRE EXPOSITION & CONFERENCE SEPTEMBER 21-23, 2004 AKRON, OH Thank you, _____ and good afternoon Ladies and Gentlemen. Let’s see if I can sqi..iee.ze 55 years of radialization into 35 minutes. I shall start with a preamble, followed with the beginnings of radialization in Franceand the United States, and will continue with the situation today, and wrap it up with the future as I see it. Because of the limited time allocated,, my speech is only about radial ply tires used on passenger cars, station wagcns., minivans, SUVs and light trucks~using passenger car type tires. P REAMBLE Revolutions, in the long run, seldom achieve the objectives of those initiating them. With the radial revolution, the objectives of the pioneers were lower tire operating temperatures and long life. However, over the years, and with the proliferation of tire types, sizes and aspect ratios, the basic product gradually became less and less revolutionary as far as long life is concerned. Keep in mind that long tire life, which means economics, was the primary promise of radialization. The life of a tire manufactured at reasonable levels of precision and uniformity, and selected to operate on a vehicle at a given load, inflation pressure and deflection, depends on the degree of road surface abrasiveness, the type of terrain, the tire architecture, the tire tread design and compound used, the vehicle speed, the severity and frequency of vehicle straight—ahead,acceleration, deceleration and cornering operations, the vehicle design effects, the meteorological/climatic conditions and, last but not least, the road hazards and lèiiel of maintenance tires encounter in the process of providing vehicle functions. Needless to say that, if tires operated only straight ahead, with no camber,toe and longitudinal forces,tire life would be great. 55 YEARS OF RADIALIZATION The evolution of the pneumatic tire, since Thomson invented it in 1845, has been directly linked to the development of cars and roads, to the correct matching of a given tire architecture and size to a particular vehicle,and, again, to the level of precision and uniformity by which tires are produced. In view of concerns about.tire structural integrity, vehicle fuel consumption, roll-over, the use of limited stroke ultra—low section height tires, tire bead unseating, etc.., attention has been focused on large, heavy, highly powered rear wheel drive, front wheel drive and four wheel drive vehicles which operate at very high speed, at times fully loaded. At the end of the day, the tires must safely absorb all vehicle operational inputs, and in the process,remain smooth—running and in one piece, preferably for 50,000 miles or more. No tire pressure monitoring system, nor the use of high load reserve tires can be effective if, in the process of wearing their treads out, tires do not remain in one piece. Another promise of radialization was lower tire rolling resistance, hence lower vehicle fuel consumption, and lower tire operating temperature. Up to a point, the benefits of such tire operational characteristics were achieved, but,in my view, not to the level of expectations originally anticipated, based on tire power wastage, rolling resistance and temperature values obtained from indoor tire testing machines. For example, a lower tire rolling resistance —2— has more of an effect on reducing the fuel consumption of a light, rQasonably dimensioned and powered, streamlined vehicle,than on the type of vehicle I previously mentioned. On the other hand, the real World, non— steady operational nature of any ground vehicle has a negative effect on vehicle fuel consumption. One of the many operational characteristics of pneumatic tires is the tire to road surface tangential force. This force increases rapidly as the vehicle propels itself straight ahead through the air and windage, particularly at speeds above 45-50 MPH, and when tire operating temperatures are low. Tires can indeed by structural] challenged when operating highly loaded and at excessively high temperatures and speed, but they can be equally challenged, dependinc upon conditions, when operating lightly loaded, at low temperatures and low speed. ~i~ie critical factor to keep in mind is tire deflectic Very early on I learned, th’~t the radial ply tire basic structural discontinuities, where the stiff steel cord belt joins the flexible radial casing, required tire design application specific compounds capable of providing a high level of thermo—mechanical performance, high fatigue and aging properties, and considerably enhanced tire intercomponent bond strength in the chemico—physical sense, particularly within and between the tire steel cord belt plies —2— and between the tire belt sub-assembly and the radial casing. All this, again, because of the promise of long tire life. In time, the industry was able to respond to these challenges, particularly when, in 1969, the year of the cap ply, Pirelli became the first tire manufacturer to circumferentially apply rubberized nylon cords over their radial ply tire 2 steel cord belt plies, banding them securely to the tire rayon cord radial body. The Pirelli CN36 became the first radial ply passenger car tire to incorporate this highly desirable, when well executed, tire design .fea~e, which significantly increased the tire structural endurance at the belt edge to radial body ply interface, and also resulted in improved vehicle steering characteristics over a wide range of operating conditions. Finally, the use of innerliners featuring a high level of tire inflation pressure retention was a major factor in improving the durability of tubeless radial ply tires. 1 Billion passenger car and light truck radial ply tires are operating daily in North America. This evolution is also taking place elsewhere in the World, even though a significant portion of i remains to be radialized. —5— BIRTH OF RADIALIZATION Radialization started in France in 1946, right after World War 2, when a patent application for a radial belted tire architecture was filed by Michelin in Paris. The final document was published in 1951. The innovative tire, named “X”, was first shown publically at the 1949 Paris Auto Show, and by 1953 was used on the equally innovative CITROEN 11 CV front wheel drive passenger car, which had been in production in France since 1934 and was wearing its front tires twice as fast as its rear tires, as all front wheel drive cars do. The “X” tires were black wall tube type, and of ~80 aspect ratio when fitted on a rim of width dimension representing 70% of the tire inflated section width. They used a highly siped tread design called “STOP”, introduced by Michelin, first in 1934 on a high section height bias ply tire, and lateron in 1937 on a then new, low section height bias ply tire named “PILOTE”, also of .80 in aspect ratio on a 70% rim. The stop tread, when used with the belted radial tire casing, was highly stabilized through the use of 3. high density steel cord tri—angulated belt plies, decoupling the tire belt/tread sub-assembly from the tire/wheel rim base through the tire flexible rayon cord radial body, In such form, the “X” tire maximized tread life for a given tread compound formulation, up to tripling it, as compared to the PILOTE bias ply tire previously used on the CITROEN 11 CV. —5— In 1957, Ptrelli commercially introduced its version of a belted radial ply passenger car tire, using 4 rayon cord belt plies on a 2 ply rayon cord radial casing. Gradually,tire producers throuqhout the World slowly radialized, some through ratifying licensing agreements with Michelin and Pirelli. Tire Engineering Performance Acceptance Criteria have indeed changed dramatically since radialization started in France right after World War 2. BADIALIZATION IN NORTH AMERICA Radialization in North America, began at the replacement tire level when, in early 1966, Sears & Roebuck started selling Michelin radial passenger car tires of tube type construction, featuring narrow white sidewalls and .80 aspect ratio on a 70% rim. These tires, as compared to those first introduced in France in 1949, differed in tread design and belt construction. Of structural significance, they had a belt consisting of 2, low density steel cord belt plies rather than 3 high density steel cord belt plies originally used in the 1949 X tires. In addition, they featured a narrow textile cord low angle bias ply,positioned under the edges of the belt package and bridging the top radial body ply. This as.:’an effort to improve tire structural integrity. -12 — The tires were warranted to last 40,000 miles under U.S. operating conditions. U.S. consumer reactions were mixed, due to vehicle ride harshness, boom, steering response and pull. You’ have to realize that, in 1966, the typical American body-on-frame car with its highly compliant suspension system aitid low pressure bias ply tires was the epitome of operating smoothness, comfort and low noise levels, and that when Sears started. to sell radial ply tires, “radial tuned” vehicles did not exist. Radial tuning means desensitizing the vehicle from unwanted tire induced vehicle reactions, not an easy job, I can assure you, and this from hands—on tire/vehicle system development experience. Prior to radialization, the then universally used bias ply tire with its absence of structural discontinuity, provided a more linear and slower development of cornering force over a wide range of vehicle operating conditions.