EHEMICÂLÂÉ ENGINEERING
the newsmagazine off the chemical world VOLUME 3 5 , NUMBER 42
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OCTOBER 2 1 , 1957
New cars, n o w g o i n g to dealer showrooms, spotlight fierce duel between nylon a n d rayon t o win tire cord market. Above, new 1958 Plymouth masquerades its features a s it streaks along o n a coast-to-coast durability r u n
Fracas in Tire Cord N y l o n a n d rayon fight for tire cord market. Struggle ensures at least one thing: better tires
INI E\V CARS are n o w moving t o dealers
showrooms, focusing attention on the running battle b e t w e e n rayon and nylon for the tire cord market. This year, 99rA of the original e q u i p m e n t tires on autos used rayon cord. Nylon, meanwhile, has sewed u p aircraft a n d off-theroad tires and most premium tires. Du Pont claims that nylon will go into about 3or/f of this year's truck and bus tires, 4 0 % of t h e replacement tires on autos. Most contested market right now is the original e q u i p m e n t market on automobiles. Nylon cord tires will b e standard equipment, for instance, on all 1958 Chrysler a n d DeSoto three-seat station wagons, t h e Chrysler 300-D, and all Plymouths t h a t use t h e Golden Commando engine ( a n optional, extra
cost package). They will also b e optional, at extra cost, on all other Chrysler cars except Plymouths without t h e Golden C o m m a n d o engine. This year, by contrast, they were standard only on the Imperial LeBaron, optional on other Imperials and on all Chryslers a n d DeSotos. Although Chrysler New Yorkers a n d all Imperials offered nylon tires as standard equipment a year ago, they switched back t o rayon cord tires for 1957, with nylon an extra cost item. American Motors, too, will offer nylon tires at extra cost on all its 1958 models except t h e Metropolitan. But its Rambler Rebel, which came with nylon tires as standard equipment this year, will be e q u i p p e d with them next year only as optional equipment. F o r original equipment use, rayon
has a slight edge in cost, vital in the highly competitive tire business. Regular rayon costs 5 5 cents a pound, the top grades 5 8 cents; nylon costs $1.30 a pound. (Prices of both fibers dropped 12 to 13r/r last year.) But cost of the finished tire, the crucial figure, involves more than the cost of cord raw material. • Cost vs. Strength. First, nylon is stronger, pound for pound, than rayon. This shows u p in the standard tire cord deniers: 8 4 0 / 2 for nylon, 1 6 5 0 / 2 for rayon. (Denier is the weight in grams of 9000 meters of cord; " 2 " means that two such cords are twisted together to make a tire cord.) As a result, a pound of nylon would equal about 1.7 pounds of rayon in typical tires with cords of equal strength (tensile OCT.
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Single twisting from beam is one step in making rayon tire cord, which accounts for 9 9 % of original equipment tires
strength, considered apart from factors like impact strength and fatigue resistance). Thus within the bounds set by nylon's physical properties, tire makers can offset its initial cost by using less of it per tire. On the other hand, nylon does not have rayon's dimensional stability. Tire makers attack this problem by hotstretching nylon cord. This makes it, in theory, dimensionally stable u p to the stretching temperature. But it also adds to t h e manufacturing cost. With all costs thrown in, tire makers can and are making nylon cord auto tires that retail for about 5rv more than rayon cord tires of comparable construction. That's the minimum cost differential; on some lines of tires it may be as much as 20 r /r or more. Because tire makers can use less nylon (than rayon) per tire, they can use less rubber per ply. This means a thinner tire body that dissipates heat better, a big factor in tire wear. But in truck tires, says R. H. Spelman of Gen24
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Tests show, says D u Pont, that tires with nylon cord resist impact better than rayon ones. This machine tests tire loads
eral Tire, nylon's strength and fatigue resistance have allowed a trend toward deeper tread grooves and thus more rubber a n d a hotter running tire. Special care must be taken in designing, compounding, and curing such tires to avoid tread cracking. Another point for nylon is its water resistance; moisture degrades rayon cord. This can be important in any tire, t h o u g h perhaps more so in off-theroad tires, which are more likely to get cut, thus exposing the cord. > Which Wears Best? Nylon's problems result mostly from its relative lack of dimensional stability. One tire man says, for instance, that nylon tires "grow" slightly in service. As a result, t h e tread rounds out and its center gets slightly more wear than the rest of the tread. F o r this reason, he says, a nylon cord tire gives roughly 5 r r less tread w e a r than the rayon model. Such comparisons are controversial. Another tire firm points out that tread wear may vary 20 to 3 0 r r , depending
on who's driving the car. Presumably, this makes the o'-r difference academic. Still a third tire firm says it finds no significant difference in tread wear. It believes the nylon tire's lower running temperature offsets its tendency to round out. Nylon's major advantages in the finished tire, says Ted Kersker of Goodyear, are its impact and fatigue resistance. This seems confirmed by the fact that nylon has displaced rayon in aircraft tires, which require a high order of impact resistance. But in auto tires, cost becomes much more important. H o w much difference is there between a nylon and a rayon tire m a d e at the same cost? The closest commercial approach to such a comparison seems t o be the tires that retail at about a 5r/e differ--) ential. At least one man with a major tire firm says h e isn't convinced that there's any notable difference between t h e two. D u Pont, o n the other hand says that, in general, a line-for-line
comparison (first line with first line, premium with premium, etc.) shows the nylon tire to have five to 15 times the impact resistance of the rayon, one and a half to two times the toughness (determined by carcass energy measurement), and better high-speed performance. Such comparisons accept a price differential between the two and do not entirely answer the initial question. It seems, in fact, to have no unanimous answer. • Detroit's View. Rayon's biggest ally seems to be the automobile industry, which controls the original equipment market. Accepting the fact that they can get a good tire with either fiber, people in Detroit look next at costs. Rayon has the edge on this score. Next, auto makers must look at tire "aesthetics." How does the tire ride? How does it sound? There are differences in the outward behavior of rayon and nylon tires, though none of them have anything to do with tire performance. T h e one that's been bruited about the most, perhaps, is nylon's tendency to take a temporary set after standing a while. The result, known in the trade as "flat spots," "morning thumps," and the like, disappears after the car has been driven a short distance, sometimes as little a s a city block. The degree of flat spotting that occurs may vary with the make of tire and the weather. And according to one report it takes *'a pretty sensitive posterior" to detect
it. Nevertheless, this is the kind of aesthetic problem the auto industrysays it must think about. • Supply Picture. Detroit must also consider supply. Chemstrand and D u Pont, the two suppliers of nylon tire cord, are selling all they can make now, and their combined production is expected to b e up by 40 to 50fA b y early next year. Also, auto makers might prefer to have more than t w o sources of supply. They now h a v e five domestic rayon sources: American Enka; American Viscose; Du Pont; Industrial Rayon; North American Rayon, a Beau nit Mills subsidiary. Rayon and nylon producers have also joined battle on the advertising front. The American Rayon Institute is moving into high gear in consumer advertising and in coordinating technical activity. Cellulose makers have entered the ad campaign, too. One point, here, is that "nylon" seems to be a magic* word, especially at the consumer level. An indication of this appears in t h e comment of a tire research man, working to reduce nylon's tendency to t a k e a temporar\' set. "Instead of doing it this way" he said, "why not use a n e w slogan: 'If it doesn't flat-spot, it isn't nylon!' " • Steady Change Expected. Tire cord is far from static. For instance, J. E. Bassill of American Enka points out that the latest Enka rayon for tire cord is the third such improvement in the past three or four years; it makes
cords 4oÇc stronger than top rayon grades of several years ago, he says. Enka is now making this fiber (SuperSuprenka), while D u Pont (a rayon maker, too) is producing a similar grade ( Type 272 Super Cordura). And other rayon makers are gearing for production. Both Chemstrand and Du Pont, meanwhile, have brought out a new nylon with improved dimensional stability. Tire makers, as always, are conducting continuous development and test programs. Du Pont, too, has a development group working on both fibers, from raw cord through fleet testing of the finished tire. Design changes in tires will probably come, too. Finer denier rayons, to go with the higher strengths, are available to tire makers for testing. At least one tire firm is thinking about higher denier rayons, something in the rangp of 2200, perhaps. The nylon camp notes that their product has been used largely in strange substitution "for IT yon. Suitable design changes in tires would take better advantage of nylon's properties, they feel. Some points in this picture arouse little controversy. One is that a very good tire can be made with either rayon or nylon cord. Another is that, costs aside, a more rugged tire can be made with nylon than with rayon. A third is that better tires are sure to result from the strenuous technical efforts being made by all concerned.
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Nylon Ties Up More of the Tire Cord Market
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Nylon's Share of Tire Production
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