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Invention & Technology MagazineSpring 2001    Volume 16, Issue 4
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The Radial Revolution


A fundamental change in the way tires are made improved automobile performance enormously—but it was a very hard change to make happen
BY TIM MORAN


ANDY BUSH DROVE A MERCEDES, WHICH WAS UNUSUAL in the United States in the early 1960s. More unusual still, the tires on his car never seemed to wear out, even though they always looked flabby and underinflated. He loved the durability of his peculiar French-built “radial” tires.

Bush was a buyer for Sears, Roebuck & Company, and it happened to be a time when Sears needed something to give it a competitive edge and America was gripped by a controversy over traditional bias tires. As a result, Bush became a figure in a revolution. Over the next decade the radial tire changed America’s driving. It forever altered the U.S. tire industry and the way automakers designed and built cars. After all the recent headlines about troubles with certain of Firestone’s radial tires, it is easy to forget how enormously the technology improved automobile handling and safety. And the story of how it emerged is hardly ever told. It took a string of parallel, seemingly unrelated developments to get radiais established in America. Some of the developments came from inside the auto industry, others from retailing. Some involved technical matters, others almost pure marketing ones.

Sears was in the midst of a corporate transition, struggling to reach a more upscale market. Any new, leading product it could add to bolster its image would be welcome. Americans, meanwhile, were becoming wearied by a series of quality problems with conventional bias-ply tires. In 1962 tire makers had changed their construction methods, reducing sidewall thickness by halving the number of plies in the tires. The engineering principle had been sound, but its implementation had left much to be desired. The lightweight, low-cost tires now being supplied as original equipment to automakers became known in the industry as “four-dollar rags,” and public opinion blamed their two-ply construction for a host of unrelated problems.

Sears made a corporate decision to find a way to abandon the unpopular two-ply tire, but the question of what to substitute for it remained. Bush thought he knew. He had already tracked down the source of his radial tires while trying to obtain a supplier for replacement truck tires. But when he had visited the offices of the Michelin company, in Clermont-Ferrand, France, he had been rebuffed as a brash unknown.

Showing up again, this time to discuss automobile tires, he still got no warm welcome. Michelin’s management, stern, paternalistic, and secretive, had its attention focused on automotive insiders and knew almost nothing about Sears. The company had long sold tires for trucks, tractors, and other heavy equipment in America, but it was not yet ready to build passenger-car tires in American sizes. François Michelin, the head of the company, put off any suggestion of a meeting. But Bush was undaunted. Louis Couderc, a Michelin executive based in the United States at the time, remembered in a 1980 interview that Bush “got into difficulties, but insisted so much that an appointment was finally granted. I remember Clermont-Ferrand sending us telexes and requesting information about Sears.”

Pierre Fougeron, then the head of Michelin’s tire operations, remembered that Bush “threatened not to leave France until he had received a final response.” In the end, that stubbornness won out. Sears archives contain an initial handwritten “treaty” between Michelin and Sears dated July 30, 1965, and in December 1965 The Wall Street Journal announced that Sears would begin selling radial tires the next year under its Allstate brand. The Sears catalogue for 1966 contained a two-page paean to the new tires. “If a firm, responsive ‘feel of the wheel’ bothers you as you drive, this tire is probably not for you,” read the blurb.

American drivers responded eagerly, even though their cars hadn’t been designed with the new tires in mind and couldn’t benefit from them fully. Most American tire makers looked on with indifference; they, along with most auto manufacturers, believed that the radial was doomed, a false trail that would burn up research money while leading to a dead end.

Radials are tires whose supporting fabric cords wrap straight across from rim to rim, instead of going diagonally like the stripes on a candy cane, as was the case with old-style “bias-ply” tires. Radiais also have durable belts of steel or fabric between the cords and the outer tread. In the 1960s most American car and tire makers believed that the harsh ride delivered by radiais made them suitable only for trucks, so experiments with passenger cars remained tentative. B. F. Goodrich was probably the farthest along, thanks to its relationship with the French tire maker Kléber-Colombes (a Michelin affiliate) and the Dutch firm Vredestein. In late 1967 Goodrich inaugurated a five-million-dollar “Radial Age” national advertising campaign for a rayon-belted product for the replacement market, and other companies began testing radiais produced to designs from their European subsidiaries and partners, but the results were inconsistent, tending to show poor performance.

Even after radiais were introduced on a few production cars, many executives remained convinced that they were a marketing fad that would pass. As late as 1971, James Roche, then chairman and chief executive officer of General Motors, was quoted in Modern Tire Dealer saying, “You won’t see a changeover to radial tires as original equipment on Detroit’s new cars in the near future. If our customers want another kind, they can get it from the dealer.” Only a few engineers felt differently, and they were mostly young, pushy ones just a few years out of school, with little to lose. But they had good reasons for their brashness.

Tires of any kind are remarkable things. Drivers tend to think of them, when they think of them at all, as balloons to keep inflated. Engineers think of them as highly sophisticated structures that perform a variety of distinct tasks. Robert Snyder, a former tire design chief for Uniroyal, notes that they present a paradox. Take a set of tires inflated to 32 pounds per square inch, load a 2,000-pound car onto them, and their internal air pressure doesn’t increase. It remains at 32 psi. That’s because a tire is not a simple bladder of air; it’s an engineered structure, as complex as a suspension bridge. The air inside is a tensioning mechanism, not a load-bearing mechanism. The thousands of individual fibers that circle the tire, kept in tension by the air, are what actually carry the load.

In an old-fashioned biasply tire, those fibers extended at a low angle of 30 to 36 degrees from one tire bead (the edge where the tire meets the wheel) across the entire structure in a long, sinuous track to finish at the same angle at the other bead. The fibers—typically made of rayon into the early 1960s, and increasingly of nylon or polyester thereafter—were layered in a crisscross pattern, and they could flex with a pantograph-type motion. Traditionally, four plies, or layers, of bias fibers were used, and they provided both durability and stiffness.

Bias-ply tires were easy to manufacture, and with their flexibility they could soften both harsh road surfaces and the rough rides of many cars. But their disadvantages were numerous. They were slow to respond to steering pressure, and when they did respond, they tended to give in to the turn all at once. As they aged and became worn, they stretched by up to an inch in diameter. They tended to develop flat spots if left parked too long in one position, and with the synthetic rubbers of the time, they lost air like mad. Worst of all was their “squirm,” the result of the duel between the tire’s native shape and the flat road surface.

Good nonbelted bias-ply tires lasted perhaps 15,000 miles. For many drivers, a new set of tires was almost an annual event.

In cross section, a typical bias-ply tire has a nearcircular C shape with a tread molded on to provide a flat surface to meet the pavement, like a round skull with a flattop haircut. Because the structure under the surface is rounded, it deflects when it meets the pavement, pushing the crown of the circle inward and pulling the tread toward that deflection. The result is called scrub and squirm.

Robert Snyder puts it this way: “What you were doing was compressing an arc into a chord. If I take a bias tire, mount it on the car, and mark a position on the tire—let’s say for our purposes that the circumference is 100 inches—now if I allow it to roll through exactly one rotation, it’s not 100 inches out that we find that mark. It’s maybe 96 inches.”

Snyder went to work for the U.S. Rubber Company (which became Uniroyal in 1966) as a chemist in the synthetic-rubber program during World War II. By then, biasply tires had already long been considered a mature technology, and improvements to them were incremental. In 1955, when he moved to U.S. Rubber’s Detroit tire laboratories, the main concern was merely to increase their durability. At the time, a good nonbelted bias tire lasted about 15,000 miles, not much longer than in the 1930s. A spirited recapping industry specialized in putting new treads on some 33 million used tires a year, but consumers saw retreads as cheap and failure-prone. For many drivers, a new set of tires was almost an annual event.

The nation’s new interstate highway system only made matters worse, causing tire mileage to actually decline. This was partly because bias tires generated a lot of heat at high speed, thus becoming even more vulnerable to uneven wear, and partly because the specifications for many of the highways required sharp sand as part of their concrete mix, producing surfaces that took a heavy toll on tires until enough pounding polished the roadways. Road-surface effects became so critical to tire lifespan that Uniroyal and other tire makers kept survey maps of the nation showing tire-wear patterns.

There wasn’t too much else the tire industry could do. Bill VandeWater, who joined Firestone in 1973 as a junior bias-ply engineer and is a manager there today, remembers well the frustration of trying to balance rubber compounds, tread patterns, and other factors to gain a slight improvement in traction without sacrificing other performance. “You would think you had the mileage where you wanted,” he says, “but if you started playing around with the tread pattern, if you started playing around with that compound, then you started sacrificing mileage.”

The concept of radial tires, meanwhile, had been introduced in 1914, when two Englishmen named Gray and Sloper, of the Palmer Tyre Company, had received a patent for the idea. Gray and Sloper had crossed cables around the perimeter of the tire radially, or straight out from the rim, to try to stiffen the tire sidewall. Their tire was never put into production (it seems to have had inherent design flaws, and in any case the technology for bonding steel to rubber was not yet developed), but the idea lingered, particularly at Michelin. By the late 1930s the company was using rubber-encapsulated steel cord to reinforce bias-ply tires for trucks, selling the tires under the name Métallic. During the German occupation in World War II, a Michelin engineer named Marius Mignol worked with existing steel technology to fashion what he called a “cold” tire, because it reduced the heat generated by internal friction. He achieved this by placing steel plies radially across the tire.

Although Mignol’s experimental tire was not roadworthy, it ran cooler and with less rolling resistance than conventional tires. It had no directional control or stability, however, until he fitted an additional layer of steel belts lengthwise along its circumference. In mock derision, his fellow engineers called the resulting network of steel a cage à mouches, or fly cage, because it looked like wire screening.

American tire makers believed the radial was doomed, a false trail that would burn up research money.

Michelin applied for a patent on the invention in 1946; it was granted in 1951. After refining its components further and testing the market, Michelin introduced its “X” tire in two sizes at the Salon de l’Automobile in Paris in October 1949. The company’s part ownership of the automaker Citroën allowed it to put the new tire into production on the innovative front-wheel-drive 11-CV car. Even Michelin’s own engineers could hardly believe what they had stumbled onto. Their innovation at least doubled the tread life of conventional tires and promised improvement far beyond that.

The radial’s key advantage, they found, was that it could set its tread on the ground without the squirm and friction of a bias tire. They compared it to a tank or bulldozer tread. The constraint of the steel belts, which would neither elongate nor compress, kept the tread from distorting, and radial cording made the sidewalk more limber and flexible, increasing the tread’s ability to conform to the road.

The tire’s reduced friction and squirm not only lessened wear but also produced fuel savings of more than 3 percent. Its harsh ride was mitigated by the relatively small size and light weight of European cars and the fact that Europe’s roads were being upgraded for smooth high-speed travel. Michelin’s X tire was quickly picked up by European automakers.

Michelin’s engineers could hardly believe what they had stumbled onto. Their innovation at least doubled tread life.

Michelin engineers went to work to improve their manufacturing process, and Michelin lawyers labored to protect every conceivable aspect of the technology; meanwhile, other European tire companies threw themselves into high gear to come up with their own new tires. Eventually, in 1951, the Pirelli company, of Milan, succeeded in patenting an all-rayon-corded version named the Cinturato. Pirelli, which originated the term radial, finally started using steel belts in 1972.

American tire makers kept abreast of what was happening in Europe, but they saw in the new radiais only a limited replacement market for the scant number of import cars in the United States—a market they were happy to let foreign firms serve. New technology was developing around the bias tire in North America; this partly blinded the industry to the importance of radiais, and so did the adversarial relationship between the tire companies, concentrated in Akron, Ohio, and the automakers in Detroit.

Bob Martin, who started as a junior engineer at Firestone in 1957, remembers that “the auto industry and the tire industry hated each other. There was no partnership in that era; you were a supplier. You were supposed to meet performance, cost, and delivery targets and then give cost cuts as well.”

High on the list of auto companies’ demands in the late 1950s were so-called low-profile tires, only two-thirds or so as high as they were wide. With their more aggressive treads they could enhance traction, while their slim profiles could please stylists by leaving the car closer to the ground, and their bigger wheels could allow bigger brake hardware. The move to produce low-profile tires opened other engineering possibilities, especially weight and friction reduction. A thinner sidewall could help with both.

That meant having fewer sidewall plies. New plastics offered strong alternatives to tried-and-true rayon, and during the 1950s and 1960s both nylon and polyester cord came onto the scene. But nylon transferred more sound and vibration than rayon and would deform temporarily if the car was left standing for a long time, and polyester had a relatively low melting point, which caused problems because of the heat generated by a tire’s internal friction.

So changing the technology while lowering costs to meet the automakers’ targets proved difficult, and quality problems arose that led to a number of tire failures and eventually the attention of Congress. Sen. Gaylord Nelson, a Wisconsin Democrat, held hearings in 1965 that led to the establishment of the National Highway Traffic Safety Administration, in part to regulate tire safety. Senator Nelson criticized two-ply bias tires as “hazardous for extended driving,” and though the thinner-sidewall tire had a sound engineering basis, the hearings devastated its public image.

In 1963 Addis Finney, Firestone’s man in Europe at the time, and Manuel Balbis, a Firestone engineer who had worked in Cuba and Akron, flew together from Geneva to the United States with a set of radial tires in their baggage. “They looked weird as hell,” recollects Bob Martin, who saw them at a Firestone test site. “First of all, they were European sizes, so they were small-looking. The sections looked small in section height, the treads looked narrow, and when you inflated them and put them on a vehicle, they looked flat. That was my perception.”

Firestone engineers met Finney and Balbis in Baltimore to test-drive the new rubber on a small Ford car. Finney, who would later become his company’s executive in charge of radial development in Akron, liked to tease the Firestone people about Americans driving on “antique tires,” but the tests weren’t encouraging.

“It was peculiar,” Martin explains. “The ride was a lot softer than I thought it was going to be, and the handling was terrible.” Bill Woodall, another Firestone junior engineer at the time, had a similar reaction: “You went over an expansion joint in the road and it’d knock your teeth out. Small irregularities were amplified. It took 15 degrees of steering wheel to hold the thing straight on the crown of the road. And the tread design made a lot of noise—why in the world would anybody ever want to make a tire like that?”

Woodall saw no advantages in the new tire. What Finney knew, and the junior engineers had yet to discover, was that American cars had to be adjusted to use the new tire correctly. The tires rode harshly because their precise handling was revealing hidden weaknesses in the cars.

A Ford engineer named Jacques Bajer (pronounced bajay) probably knew more about the subject at the time than anyone. Headstrong, defiant, and articulate, he had arrived in the United States in 1955 from a French truck-making firm and had found a niche in the relatively unexplored world of quantifying tire and suspension interaction. He defended his turf so ferociously that Ford executives took to calling him Jack Badger.

In 1962 Bajer and his team put together an experimental piece of test equipment they called a tire-uniformity machine, to retrieve dynamic data on what went on as a wheel rolled under pressure. Such machines have since become commonplace and refined. Bajer stressed the need to analyze tire, vehicle, and road together rather than think of the tire alone. And he wanted hard numbers. His persistence led to a string of Society of Automotive Engineers publications explaining numerical analyses of skid and rolling resistance, wet traction, nonuniformity among tires—and the behavior of radial tires on American cars. In 1965 Automotive News could report that “for the first time, Detroit auto makers are actually setting the design requirements of the 35 to 45 million tires they purchase annually.” Their demands had never before been truly quantifiable.

Bajer knew about radiais from his European days, and as a result of his prodding, Ford issued a confidential report to its management in 1964 discussing the new tires’ potential. The next year, Bajer equipped a specially constructed unibody Ford Falcon with radiais and a “tuned,” as he put it, suspension. To make that suspension work, he had to undo some of the tweaking that made bias-ply tires ride well. Because bias tires tended to react slowly, they required tight steering; radiais needed much less steering input. To soften the jolt when radials’ belts hit pavement inequalities, special rubber bushings were installed to let the wheels fall back slightly. And the drive shaft needed isolators to prevent rear-tire noise from feeding into the passenger compartment. Bajer was betting that the strengths of the new tire—quick steering and the ability to absorb big bumps —could be an advantage in a properly tuned car. And if the car no longer had to compensate for tire weaknesses, it could dump pounds of weight and free engineers to focus on new vehicle construction methods.

He had as a consultant another Ford engineer named Fred Hooven, who had a broad vision of the future. Hooven’s work had ranged from contributing to the early development of radar-guided aerial bombing to the esoterics of noise and vibration analysis. He found that the experimental car completely outclassed a Falcon on bias-ply tires, and he testily told Ford executives that their shortsighted reliance on conventional tires and suspension systems was holding back leaps in quality. They told him radial tires were too expensive for production cars; he insisted that prices would come down as volume went up.

The new radials gave a harsh ride at first because their precise handling was revealing hidden weakenesses in American cars.

Ford took the hint. The company began developing radial-tuned suspensions for its Lincoln and Thunderbird cars, and along with the other major car makers, it offered optional radiais on some models beginning in 1967. Only about an eighth of a percent of car buyers chose them, and even at that rate there were supply problems. Ford was buying the radiais from a variety of manufacturers, and the American-made ones suffered from quality problems that the dealers usually solved by replacing them with Michelins.

Meanwhile, the landslide of change that Andy Bush’s determination had started was bringing big benefits to Sears. The company’s share of the U.S. tire-replacement market jumped to 25 percent for a few years before settling back to a sturdy 10 percent as other companies began selling radiais. John Breslin, a former vice president for sales at Armstrong Rubber, which supplied Sears’s conventional tires, said the radiais gave Sears a “premium” retail image while breaking the ice for auto manufacturers and tire makers alike. “It certainly made them money, and it certainly established them as a real tire supplier,” he says. Unfortunately, Bush had no chance to enjoy his coup; he died soon after the radiais were introduced.

In 1968 the top executives of Ford and Michelin met to arrange a groundbreaking event: Ford would launch its 1970 Lincoln Continental Mark III with radial tires as standard equipment, and Michelin, under its own name this time, would be the exclusive supplier. But there was one stumbling block. Ford executives feared that the radiais’ price would be unaffordably high, Michelin that it would be unaffordably low. The impasse was broken when Pierre Fougeron reached into the breast pocket of his suit coat and placed a slip of paper on the table reading “$19.37 per tire.” That was not even five dollars more than bias-plies for the Lincoln. The deal was sealed. A leading American car would ride from the factory on radials.

In 1973, 11 percent of GM cars and 26 percent of Fords were being equipped with radiais. Two years later, it was 86 and 90 percent.

Ford’s move excited automotive reporters, challenged tire makers, and launched a flurry of industrial espionage. Many tire makers fought against the radial; they were reluctant to spend millions retooling their factories for a product that would greatly reduce their sales of replacement tires, always a much more lucrative business than original equipment. Goodyear in November 1967 launched its novel Polyglas bias-belted tire, with polyester cords and fiberglass belting. The Polysteel followed soon after. Goodyear promoted its hybrid technology so hard that by 1970, 86 percent of new U.S.-built cars were equipped with bias-belteds. General Motors, which at the time bought nearly 30 million passenger-car tires a year, or a sixth of the total for the entire nation, stayed for the moment with bias-belt technology.

Rubber Age magazine even announced in 1970 that “the battle between radial … and belted bias ply passenger car tires is over—the latter having won.” The claim was premature. Cadillac, not about to be left behind by Ford’s Lincoln, demanded radiais in 1972. The next year, GM was buying more than three million. At that point, says Bill Woodall, “the whole industry was going to be asked to supply steel-belted radiais, and I believe Michelin was probably the only original equipment maker that had the process down.” In fact both Firestone and Goodyear had bought licenses from Michelin back in the 1950s for the right to produce steel-belted tires, but Michelin had offered no technical guidance to go along with the licenses.

The French company jealously guarded its secrets, assigning workers to specific aspects of tire making and ensuring that only a select few at the highest levels learned the entire operation. American tire engineers repeatedly told stories, which Michelin wouldn’t confirm, of equipment repairmen being lowered through skylights or led through canvas-walled corridors so they would see only the tools they were there to work on.

Without the necessary manufacturing know-how, early American efforts at steel-belteds were awful. Tire makers had access only to their own ingenuity and the Pirelli process for making textile-belted radiais, which the company licensed widely. So, says VandeWater, “We experimented a lot. We looked at cloth belts. We looked at rayon belts. To get the same stiffness you got with two steel belts, you had to go to four belts in rayon. You ended up with a tire that was really bulky and really heavy.” Making such tires perform well on an actual car was an art in itself, and customers were advised not to rotate them. As VandeWater puts it, “Once you got that radial working on a car you didn’t touch it. You didn’t even think of touching it.”

Even without all the research involved, gearing up for manufacturing was expensive. A whole new section had to be added to tire factories, with a room where delicate steelwire or glass-fiber cords were woven into belting. Getting rubber to adhere to the materials was even more difficult; rubber doesn’t like to grip steel, so steel-cord belting usually had to be brass-coated in the process.

American manufacturers tried to break in with fiberglass-belted radiais, but the first generation of those developed cold-weather breakage problems. The next generation was fine, but by then consumers had already dismissed the glass belts, and automakers weren’t about to risk their reputations on them.

The machinery that was used in assembling the tires had to change too. Bias tires were built in layers over long, barrel-shaped drums and then inflated to their final shape during heat curing. Radials needed an extra stage in the assembly process and went to the curing stage in a shape much closer to their final form. This demanded much greater precision. The industry faced massive recapitalization, a steep learning curve, and increasing demands from its customers.

“I’d get called out of bed at 11:30 at night to go to a meeting at Ford,” Martin remembers. “’d go to the Wixom assembly plant,” in Michigan, “at 2:30 in the morning, pick up tires, and have to drive them to Akron to get them analyzed because somebody was having a problem with them.” Tire makers hired engineers away from their competitors and then grilled them for any process tips they could find. Michelin men were particularly prized, but often their knowledge of only one step was more damaging than helpful. And in Akron, the center of the tire-building industry, orders for new tools were carefully farmed out to distant machine makers to keep competitors from learning about them.

Robert Snyder once made the mistake of casually mentioning to a colleague from another company that engineers he worked with at Uniroyal thought they could build radiais in a fairly simple clamshell mold. “Within a week, two million dollars in new mold orders were canceled,” he says, shaking his head at the memory.

By 1973, 11 percent of GM cars and 26 percent of Fords were being equipped with radiais. The numbers jumped to 86 percent and 90 percent respectively by 1975, despite a sharp recession that put pressure on car makers to cut costs. In the 1990s, even the compact spare tire shifted from bias to radial construction. Today, a typical tire for a large automobile weighs about 25 pounds, down from 32 pounds in the late 1960s. Top-of-the-line models are warranted for 80,000 miles of tread life, and even at a modest 50,000 miles, they represent a huge environmental saving. If old-style nonbelted bias tires were still standard equipment, Americans would replace more than 500 million of them a year. Instead, only about 275 million tires are discarded, according to John Serumgard, chairman of the Scrap Tire Management Council. When burned—and they are typically used as fuel in high-temperature cement kilns—tires give up about 13,000 BTLPs per pound. The nation’s stockpile of old tires is gradually being reduced as landfills and tire piles are cleaned up and cleared out; by current estimates, only 500 million remain from scrap piles that held between two and three billion in the late 1980s.

Making a tire takes about seven to nine gallons of oil, so fewer tires means less use of petroleum resources. And in the mid-1980s, GM estimated that one year’s new cars saved more than 20 million gallons of gas just from the radials’ diminished tire friction. “It may not sound like much,” says David Wood, a GM tire-engineering executive, speaking in the terms of a vast industry, “but in the end we’d like to save every million gallons we can.”

It wasn’t easy to reach those savings, but the radial tire’s overpowering technical advantages, combined with some strong personalities and parallel developments, made it happen. Daniel-Guy Denoual, the author of a 1980 Harvard Business School thesis on radiais, which studied how slowly the American tire and automotive industry had recognized and adapted to the technology, points out that tire imports rose from $88 million in 1967 to $800 million in 1976, and exports did not keep up, increasing only from $70 million to $275 million. Passenger-car radiais were largely responsible for the change. “The radial tire, in phenomenological terms, represented some kind of a ‘once in a lifetime event’ for many of the producers, users and suppliers involved,” Dénouai wrote. “In the most simple terms, most producers grossly underestimated the strength of the demand pull which the radial generated.”

Tim Moran is a freelance writer who concentrates on business, automotive, and technical subjects. He lives in Michigan.

 
From Iron to Air
Tires Before the Radial

Tires began as a durable material circling a fragile wheel, such as a steel tire on a spoked wooden wagon wheel. I So when inventors first came up with better tires, they didn’t quickly think of the pneumatic rubber kind we know today Long after air-filled versions became common, they were seen more as an outer layer than as an independent structure.

Vulcanization, discovered in 1839 by Charles Goodyear, made rubber durable enough for tires for the first time. But the earliest air-filled tires didn’t put the rubber on the outside. They were buggy tires invented by Robert William Thomson, a Scottish engineer who in 1845 patented a riveted leather wrap bolted to the wheel rims, supported I by an inflated rubber-coated canvas inner tube. Thomson continued to patent key pneumatic-tire concepts up to his death in 1873. Not until the 1888 patent issued to John’s Boyd Dunlop, a British veterinary surgeon, however, did inflated rubber tires come into their own, at first for bicycles and tricycles (including that of Dunlop’s nine-year-old son, whose bumpy rides had inspired the invention).

Carriages and wagons also used pneumatic tires, and when automobiles came along, the first ones fitted to them were so-called clincher tires. These had “beads,” or inner rims, made of rubber and formed with a barb to let a mechanical fastener hold them on. Soon after, other inventors brought forward the idea of using a wire cable to form the bead of the tire, with that bead nesting inside a flange on the outer rim of the wheel—the so-calledf straight-sided tire. At about the same time, tire treads began thickening and being patterned for better traction.

In the 1930s, new, synthetic materials such as rayon replaced cotton in the tires’ plies, greatly improving the strength of their cord reinforcement. Synthetic rubber for increased durability emerged in Germany in the late 1930s. Then tubeless tires, a wartime project of B. E Goodrich for which a patent was granted in 1952, melded all of the pneumatic tire’s features into the single, durable unit today’s drivers are familiar with.

By the time radiais hit North America, tires were already very complex structures, although their behavior was only beginning to be truly understood through laboratory testing and mathematical modeling.

—T.M.


 
Getting It Wrong
Firestone’s big recall problem—in 1978

Customers who bought Firestone’s “500” steel-belted radial tires began having problems with tread separation shortly after the tires were introduced in the early 1970s. But when they brought the tires in, the company couldn’t understand why its new flagship product was failing. Executives stonewalled. They blamed consumers for poor maintenance or bad driving habits, and the company resisted outside inquiries. Finally, in 1978, the U.S. government pressured Firestone into a “voluntary” recall of what eventually totaled 8.7 million tires, citing figures showing 41 deaths and 65 serious injuries attributable to the tread separations. The recall nearly crushed the company and may have helped enable Japan’s Bridgestone company to purchase Firestone in 1988.

But the recall couldn’t crush radialization. Even with Firestone’s problems, the advantages of the new technology were obvious to industry and consumers alike. “It was never going to die. It had too much to offer,” remembers Bill VandeWater, who was an engineer in radial sales for Firestone. Still, “we did it wrong, and it was very difficult to keep morale up during those days. It just seemed like everything we did was wrong. We fought the whole system, we were blaming it on consumers, we were doing all the wrong things.”

When Firestone engineers finally dug into their tires to find out what was happening, rusting turned out to be the answer. Every tire receives cuts, many of them deep enough to reach the belting inside. Firestone’s steel belting in the 500 was constructed of bundles woven from five cords. When a cut penetrated the tread, the cord design allowed salt-carrying water to wick along the cording, often all the way across the tread. The steel would rust, and a separation point would be created within the tire. This was a problem that developed over time—generally a year or more—regardless of how many miles the tire had been driven. “We didn’t understand the mechanism,” VandeWater concedes. “As soon as we realized that, we started making tires a little bit heftier, testing them in more overloaded conditions, testing them longer.”

Firestone installed salt-bath areas in its test tracks and intentionally slashed tires to study rust and oxidation wear. The company came up with a new tire, named the 721, with a steel structure of seven cords over two and a spiral-wound cord to hold the bundle together. One of VandeWater’s jobs was to sell the Ford Motor Company on the tire; it wasn’t easy being a Firestone engineer in those post-recall days.

But the irony of the Firestone 500 failures was that they might never have happened during bias-tire days. Back then, tire life had been so low that there wasn’t enough time for the belting to deteriorate. Nonetheless, Firestone was alone in mishandling a problem that other manufacturers were also facing. “Actually, in talking to people from other companies, we found our situation was very comparable to theirs,” VandeWater says. “They were having the same problems in the field that we were. It was just that when their customer came in with a problem, they’d say, ‘Sure, we’ll fix it.’ We said, ‘No, it’s your problem.’”

In the end, the Firestone 500 still turned out to be one of the best-selling radial tires ever, and the need for new durability testing was proved beyond a doubt.

—T.M.


 
 
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