Tires from an engineering perspective

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Tires from an engineering perspective

Jacques Bajer's work at Ford Motor Co. from 1955 to 1970 changed the automotive and tire industries for the better. The French-born engineer treated automobiles and tires as a system; his Ford-led team created the tire uniformity grading machine in 1962 and introduced the low-profile tire in 1964. He also is credited by many in the industry with putting America on radial tires.

In 1970, Bajer formed his own consulting company, Tire Systems Engineering Inc., located in Grosse Pointe, Mich. The firm specializes in the design of advanced manufacturing systems for the economical mass production of tires, power transmission belts, lathe-cut seals and air springs. More than 30 years later, he still stresses the need to analyze the relationship between the vehicle, tire and road.

MTD: While you were with Ford, you had the reputation for demanding high standards for products and developing scientific testing systems to make sure the products met those standards. Do you see this level of testing by vehicle manufacturers today?

Bajer: I have not kept up with the details of the currently used OE tire validation procedures. I can only hope that they follow those that I had originally developed over many years, and applied to the first release of OE radial ply tires on American cars (in 1968).

More important than validation is to ascertain that once the tires are released for public consumption, they are produced at consistently high-quality levels and will not fail catastrophically. No DOT, ISO, QS, etc., as recently demonstrated, can guarantee this, because tire quality is a matter of high vigilance, seriousness, professional conscience and capabilities, applied by all involved in tire and vehicle development and production.

MTD: During the events surrounding the recent Firestone recall, "experts" kept referring to nylon overlays. Some went so far as to say that nylon overlays would have prevented the recall. What exactly do nylon overlays do, and are they necessary for a tire to perform properly in an SUV application?

Bajer: The primary role of the nylon overlay is to improve the tire's resistance to belt-edge separation, a condition that can develop from the effects of a combination of adverse tire operational factors such as flexural strains, stresses, intra-carcass pressure and heat build-ups concentrated at the tire belt-edge zones, the most vulnerable part of a radial-ply tire. This important tire construction detail should be incorporated into all radial-ply tires produced.

MTD: In the aftermath of the recent recalls, have you seen or heard about any changes that will prevent a recurrence in the future?

Bajer: When, in 1978, Firestone was first ordered by NHTSA to recall millions of their radial-ply tires that were subject to tread/belt separations, Firestone improved its tire design and manufacturing process. What may be implemented this time to prevent a recurrence of this problem in the future is stricter tire design and manufacturing engineering disciplines aimed at producing consistently high-quality tires; development of tires on a much more "vehicle application specific" basis, with more emphasis placed on road/tire/vehicle/driver system interactions; and stronger consideration given to the environment within which the vehicle operates.

MTD: You've long been a critic of ultra-low aspect ratio tires. Would you explain your rationale? As a follow-up, if the technical advantages are not there, then what do you feel is the reason for tire manufacturers producing them?

Bajer: The most important dimension in a pneumatic tire is the section height. This dimension should be established according to the maximum load the tire is to support plus an adequate reserve, the type of vehicle service required, and again, the environment within which the vehicle operates. If a tire does not provide for a sufficient section height, and is inflated at higher pressures than desirable, high stresses are generated within the tire structure, more forces are transmitted to the wheel and other vehicle components, and structural damage can occur to the tire, the wheel and adjacent vehicle components.

There are three basic reasons why excessively low section height tires are used today. One, they weigh less and, consequently, cost less to produce as compared to high section height tires of equivalent capabilities.

Two, vehicle stylists have significant influence on tire/wheel system design. Paradoxically, the cast aluminum alloy wheels on which these 16-, 17-, 18- and 19-inch tires are fitted weigh and cost more as compared to steel wheels of advanced designs.

Three, vehicle development engineers are obsessed with high tire cornering power and fast tire steering response.

I'm not against a decent ratio tire. But vehicle designers should recognize the fundamental usefulness of pneumatic tires and go back to basics.

MTD: Goodyear has placed its hopes in polyurethane tire development with Amerityre Corp. In the words of Amerityre's CEO, the company has "reinvented the tire" with its monolithic tire construction, closed cell technology and use of polyurethane, which, he adds, is three times more durable than rubber. Are we really that close to replacing rubber with polyurethane?

Bajer: A pneumatic tire is not monolithic or isotropic (a structure having the same properties in all directions); it is just the opposite. A pneumatic tire is anisotropic, which means it has different properties in all directions. To perform its functions, a pneumatic tire needs a cord armature to efficiently sustain the stresses and strains the tire is subjected to in service, and to keep its dimensions over time.

It is not possible, on an economic weight basis, to provide sufficient stiffness in a pneumatic tire using a non-cord reinforced elastomeric material to contain the air pressure, without the tire generating high surface tensions which would result in the propagation of cuts and flaws because of the uncontrolled energy elastically stored within the tire. Therefore, the future of a cordless polyurethane tire for highly dynamic vehicle application is doubtful.

However, I have been, and still am, a firm believer of tire design and manufacturing process simplification, and of producing more durable, more uniform pneumatic tires. The key to the success of such development is an automated, precise and rapid application of the tire reinforcing cords and beads, combined with the usage of a variety of judiciously chosen oligomer compositions -- and not necessarily urethane -- in conjunction with the liquid reaction injection molding process.

If such a tire becomes a reality, it would dramatically alter the tire industry.

MTD: Tire innovations are almost always evolutionary, not revolutionary. For example, on the raw material side, silica is slowly replacing carbon black. On the construction side, all the companies are working on run-flat technology. On the design side, unidirectional tread designs are optimizing performance at all wheel positions. Which area of the tire lends itself to the next big innovation? How much does vehicle design affect tire design innovations?

Bajer: Radialization, no doubt, represented a consumer product innovation. But the tire, to be universally applicable on vehicles, required another equally important innovation, which in 1963 I called "road/tire/vehicle system tuning." This significant development eliminated the then-conventional wisdom, and should not be ignored.

As for silica, it made possible a reduction in tire rolling resistance without adversely affecting other important aspects of tire performance. However, I believe that the future lies in the use of oligomers, because such materials exhibit much more homogenized structures and a higher order of physical characteristics and oxidation resistance as compared to currently used silica- or carbon black-filled tire compounds.

As for run-flat tires, there are two basic types. The self-supporting type originated during World War II in pre-radial tire days for military vehicle applications, and was first commercialized for passenger car applications by Dunlop (the Dunlop Denovo) in the early 1970s. However, the Denovo tire, although radial, violated the basic principles of radial-ply tire architectures, hence resulting in a reduction of typical radial-ply tire performance.

The internal supporting platform type has been offered for special vehicle applications for years. This approach limits tire deflection, and, under run-flat mode operating conditions, can overstress the tires, the wheels and other vehicle components. So, before such a system can be used on a universal basis, a comprehensive road/tire/vehicle system validation process must be conducted.

As for unidirectional tire tread design, I am for vehicle application-specific tires, and for optimizing tire performance at all wheel positions, as in the case of a Class 8 tractor/trailer, as long as tire life and consumer convenience are not compromised. More than tread design is required to optimize tire performance at all wheel positions. Vehicle design certainly affects tire performance. Vehicle design also affects tire design innovation.

MTD: Imported vehicles are gaining more market share in the United States every year. How much are the differences in vehicle manufacturing processes driving that? Are there significant differences between Ford, GM, Chrysler and imported car companies?

Bajer: There are no fundamental differences between the manufacturing processes used by foreign and American vehicle producers. U.S. consumers have, to date, experienced higher value through the purchase of foreign vehicles, particularly vehicles like the Toyota Camry, Honda Accord, Volkswagen, etc. -- those purchased by ordinary Americans. Currently KIA and Hyundai offer 10-year/100,000-mile warranties. To provide such warranties, the car manufacturers must be highly confident that their vehicle development and manufacturing processes are conducive to consistently produce high-quality vehicles in order to minimize warranty costs. The same principle applies to tires.

MTD: OE tire manufacturers have complained for years that vehicle makers continually squeeze them on price. Price became an issue in the Ford/Firestone controversy when Goodyear claimed it had turned down a Ford offer to supply early models of the Explorer with tires because it couldn't afford to meet the specifications based on the price Ford was willing to pay. Are OE tires a loss leader for tire manufacturers?

Bajer: Radial-ply tires have provided outstanding value to consumers. Although the product is an essential component of vehicle operation and safety, it commands insufficient respect and is priced extremely low, particularly at OE levels. In the 32 years since their OE introduction to the American automotive market, OE radial-ply tire prices have doubled, while retail vehicle prices have increased six-fold. Unless this trend is altered, OE tires will remain a loss leader for their producers.

MTD: Is the building of today's radial tire as complex as it was in, say, the early 1980s? Please highlight the important aspects of economically producing a consistently high-quality radial tire on a mass production basis.

Bajer: Radial-ply tires today are fundamentally just as complex as they were 20 years ago. Ten different rubber compounds enter into the construction of each of them. The tire manufacturing process is complex, capital intensive and requires an elaborate quality surveillance system. All aspects of producing radial-ply tires at consistently high quality levels are important.

As for the economic aspect of radial-ply tire production, it has become quite problematic for the tire manufacturers, and this in no small way is due to the high proliferation of tire types and sizes currently marketed. Such a high array of tires is not really determined by the true usefulness of tires, but rather by the competition for consumer attention via marketing techniques, together with the significant influence of vehicle stylists. The results are drastically reduced production economies of scale, together with a high variety level of replacement tire inventory and consumer confusion at tire replacement time.

There are, however, sound mathematical principles from which the most economical range of tire sizes and types can be produced. It is interesting to notice that in the last three or four years, vehicle producers are becoming concerned with their own proliferation of vehicle types and styles, as well as their high variety of powertrain, chassis and body systems.

MTD: Michelin has its C3M process. With Pirelli it's MIRS. Continental has trumpeted its Modular Manufacturing Plant, or MMP. But after initial hype, automated tire making doesn't seem to be moving forward very quickly. How far along are the various tire companies in developing widespread automated tire manufacturing plants? Just how close are we to completely automating the industry?

Bajer: Michelin and Pirelli have recognized the current tire proliferation and lack of production economies of scale dilemma confronting them, and, as I originally proposed 10 years ago at a tire conference, are "demassifying" their tire manufacturing process ("Rethinking the tire manufacturing process," Modern Tire Dealer, May 1992 issue). Michelin and Pirelli are implementing the core built/core cured direct green tire component formation application system, using conventional tire compounds. As for the core built/core cured tire manufacturing method, it dates back to the dawn of the tire industry when both tires and automobiles had yet to reach the mass-production stage.

The questions are: Will the C3M and MIR systems contribute to a reduction in tire production costs? Will they reduce the currently experienced level of tire non-uniformities and improve tire-operating smoothness? Will they prevent or reduce tire structural integrity degradation? Will tire prices be reduced?

As for the non-uniformities developing along the currently used tire manufacturing process, the condition is inherent to the type of tire compounds used. This limits non-uniformity related tire operating smoothness as well as the tire fatigue resistance, because the currently used tire compounds do not exhibit a perfect level of homogeneity. To completely automate, tire production will require fundamental rethinking, starting with the compounds.

MTD: Twenty years ago, you said that the entire manufacturing process hinged upon the raw materials and the feed stocks being very consistent. Have the suppliers to the tire manufacturers improved the quality so that this is no longer an issue?

Bajer: Tire raw materials, feed stocks or semi-finished products have improved, but not to the level I expected. Again, for these issues to disappear, a change in fundamental thinking is required.

MTD: What do you see as a future for domestic passenger, light truck, medium truck and OTR tire remanufacturing?

Bajer: Replacement radial-ply tire prices in the U.S. have not come down over the last 35 years. They have, at best, kept up with inflation. In 1966, four replacement Michelin 195-14 whitewall radial-ply tires were sold by Sears for $160. By 2001, the tubeless version of the same tires was selling for $400 at Sears, a 2.5-fold increase. However, the price of the vehicle on which these tires would be fitted increased six-fold or more since 1966.

It is simply not economical to remanufacture passenger car or light truck tires today. As I indicated at a conference years ago, the remanufacturing potential of any tire is directly proportional to the original tire quality, and the operating conditions the tires are subjected to. Many tire casings do not pass inspection due to irreparable internal and external damages discovered at casing inspection and buffing time. The situation is fundamentally the same with Class 8 truck tire casings. However, due to the type of tires used on Class 8 trucks (whole steel cord dual tires), tire remanufacturing is economically more appropriate.

Aircraft tire remanufacturing, with the exception of the radial-ply tires of the supersonic Concord, which they don't retread, also remains a viable business, but the tire-operating mode is quite different. So is the tire maintenance.

As for OTR tire remanufacturing, I can only think of the Caterpillar-designed, developed and produced core built/core cured beadless radial mining tires of 20 years ago. These very large tires lasted so long, tire remanufacturing was not being contemplated. These tires also had removable treads.

MTD: What are the major breakthroughs that must be accomplished by tire manufacturers in future years?

Bajer: Before anything of significance can be accomplished, the relationship between vehicle and tire producers must be improved. However, two basic conflicting factors face both of them today: 1. If the tire selected by the tire manufacturer for a given vehicle application is too big, the vehicle manufacturer will complain that it is too heavy; that not enough tire clearance can be provided within the vehicle wheel arches; that the tire price is too high; and that, therefore, vehicle weight and cost will have to increase. 2. If the tires are too small, the vehicle manufacturer will complain that the tires could be overstressed, hence not be able to carry the load; that they limit road shock absorption; and that they do not provide adequate steering response and tread abrasion resistance. In the meantime, large diameter, heavy, expensive cast aluminum alloy wheels that can barely match the physical characteristics of well-designed and produced steel wheels are used. Catch 22?

As for the major breakthroughs that must be accomplished by tire manufacturers in future years, let me quote my late friend Tom French, who was director of tire engineering and development at Dunlop, and with whom I worked closely from 1962 until he passed away in 1994: "Any changes are likely to be slow, and thus the cord reinforced rubber pneumatic tire will essentially remain an engineering component which is awkward to produce, but which has a guaranteed future because of its unique and irreplaceable contribution to most forms of wheeled transport."

Let me add to this my prediction that future changes will be much more brutal than the industry changeover from bias to radial-ply tire production in the 1970s. In the meantime, I consider uniformity, precision, structural integrity, puncture resistance, vehicle lifetime tires -- perhaps 15 years -- and improved/simplified tire replacement and service the major projects tire manufacturers must undertake.

MTD: What can vehicle and tire manufacturers do to help independent tire dealers survive?

Bajer: Replacement tire dealers should only sell and service tires, wheels and valves that have been produced according to the "Performance Acceptance Criteria" of the vehicle producers. However, a certain percentage of all tires produced do not meet the OE criteria, and the percentage varies between tire manufacturers. The question is: Where are the rejected tires ending up?

Tire, wheel, valve and vehicle manufacturers should correctly train tire dealers and make sure that they are well-equipped to do a good job and that they are aware of, and understand, the OE tire/wheel/valve system Performance Acceptance Criteria.

Finally, trade associations representing the interest of tire dealers should actively promote the participation of the vehicle and component manufacturers in assisting tire dealers.

MTD: Thanks, Jacques.
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