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Unfortunately, switching to tires of a different profile is even more complicated than making choices about handling and figuring out if the new rubber will fit inside the wheel wells. Whatever profile is used, the overall diameter of the tire and wheel should stay the same as it was originally. Otherwise, the torque characteristics of the car will change, the speedometer will become inaccurate, and there may be problems with electronic engine control systems that sense vehicle speed at the transmission.

GROWING HEAPS

Each year, U.S. car and truck owners discard almost a quarter of a billion tires. Of course, these marvelously durable monuments to our inventiveness don't just go away. Nearly 30% get buried in landfills, only to float to the surface decades later. Another 60% lie around on the surface in random dumps or stockpiles, threatening fires such as the infamous Winchester, Virginia, disaster of 1983 and '84, or serving as breeding grounds for mosquitoes carrying diseases like LaCrosse virus or dengue fever.

Less than 10% of all the tires discarded this year will be retreaded, and by 2000 as little as 2% may see reuse. A shame, since it's only a small part of a tire, the tread, that wears out. The recapping process is essentially the same as the final stages of new tire production. New tread and sidewalls are vulcanized to the stripped carcass. If the core of the used tire is in good shape, and care is taken in the recapping, retreads can be nearly as durable as new tires. In fact, there is a stringent set of quality-control guidelines set down by the National Tire Dealers and Retailers Association. A good recap will sport a yellow, black and red sticker giving it an "A" rating.

At present, only a minuscule percentage of junk tires is actually being recycled for the rubber. Technologies are available to allow the augmentation of new rubber with used, but they're unlikely to be widely adopted by tire companies until petroleum price hikes make them more economical.

There's also interest in burning tires to produce electricity. A plant being built near San Francisco will handle about 4,000,000 used tires per year, and more ambitious projects are in the works. Again, economics, driven largely by the expense of controlling pollution from any combustion source, is the limiting factor.

Whatever the means, the burden of discarded tires on our environment must be controlled. We can use only so many backyard swings.

WHAT ABOUT STUDS!

Plastic or metal studs set into the tread of a tire can dramatically improve grip on ice. They are really the only substitute for tire chains when conditions are very slippery, and they can be used for limited periods on dry pavement at legal speeds with no worse effects than rapid wear and a lot of noise. Because their grip can be up to 50% greater than the bare snow tires they're mounted to, they should be fitted to all four wheels to balance handling.

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