Inventing a New Wheel

French Tire Maker Francois Michelin once boasted, "The automobile is an accessory of the tire." Italy's Pirelli company is trying hard to prove the point. The leading Italian rubber manufacturer has rolled out a prototype tire that, according to company officers, practically eliminates the chance of a blowout or the need for a spare; when deflated, it can run for more than 100 miles at cruising speeds.

The secret is in the tire's shape, which in cross section is roughly triangular (see diagram). In a conventional rounded tire, air pressure puts a heavy outward force on the sidewalls; a puncture causes the tire to collapse abruptly. By compressing the sidewalls downward, the Pirelli tire's triangular shape diverts much of this pressure to where the rubber meets the road. Also, the tire contains much less air to begin with, and the rubber is thicker. If punctured, the tire merely deflates gently, allowing the driver to roll along on essentially solid rubber until he can reach a repair station.

One technical advantage, according to Pirelli: since the all-rubber sidewalls are not under great tension, they do not have to be reinforced with textiles, steel or glass, as conventional tires are now. Thus the manufacturing process is much simpler and easier to automate. One disadvantage: any auto manufacturer would have to redesign his wheels to use the new, smaller Pirelli tire.

Pirelli men claim that this is a potential plus. The space freed by the smaller tires and by not having to carry a spare, they say, can be used to contain improved suspension and braking systems. Though nobody is yet building such a car, Pirelli men are discussing their new tire with auto manufacturers and figure that it could go into mass production in two or three years.

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