Spare tire goes the way of the horse and buggy

Mr. and Mrs. Motorist, you can say goodbye to the spare tire. US carmakers are making it so hard to get a full-size spare tire any more that by the end of the decade the spare may be completely eliminated.

The substitute in the car trunk on 1981-model cars is most likely a high-pressure, skinny tire on a special rim, or a compact doughnut that inflates to the size of a tire when connected to a pressurized cannister.

The nation's automakers, which have been shaving ounces here and there to make cars lighter and cut fuel consumption, have been demanding a replacement for the 40- pound spare tire and rim for a long time.

The alternatives are limited, however, since the American public has loved spare tires about as much as babies love pacifiers.

The first step in training motorists to trust their tires was to install longer-lasting radials. The next step was to introduce the minispares and inflatable spares. Full-time spare tires, which were offered as options in recent years, now are impossible to order on many cars.

The new tires are entering the market that may someday eliminate the spare tire entirely.

The first concept, and farthest from acceptance, is a tire with thick sidewalls -- thick enough to support the weight of the car even though the air has escaped. The problem with that type of tire is devising a system to warn the motorist that he or she is running on a damaged tire and that immediate action should be taken.

Getting that information from a spinning tire to the dashboard is a complicated task.

Warning devices for all four tires now cost more than $100. Until that cost can be reduced to a more reasonable level, the self-supporting tire will have a slow acceptance, according to auto and tire manufacturers.

The advantage of the self-supporting tire is that it can go from 40 to 60 miles -- far enough to get to a service station -- at about 45 miles an hour without damaging the tire.

A longer distance would create an internal buildup of heat that could destroy the tire.

Another concept is one introduced for the general market by Uniroyal and Firestone. Uniroyal, which has undertaken a strong media campaign for its Royal Seal, says its tire can help prevent about 70 percent of all disabling, premature tire failures. The Royal Seal contains a thick liquid that flows into the puncture and automatically seals the leak.

Since 90 percent of all premature tire failures are caused by punctures three-sixteenths of an inch in size, it is expected that the Royal Seal will handle most road emergencies, according to Sheldon Salzman, president of Uniroyal's tire division.

The answer to the spare time, however, is not inexpensive. Minispares and inflatable spares sell for as much as 30 percent less than full-size spare tires , thus cutting the cost slightly, according to tiremakers.

But the self-selaing tire, which can be ordered on a number of cars this year , will cost an additional $100 a set. The problem is, you'll never know if you got your money's worth because if the tire works, you'll never know it was punctured.

One thing to keep in mind these days is that tires are selling at very competitive prices.

The tire companies are suffering along with the domestic auto manufacturers; and perhaps even more so because of the decline in the economy.

Tire sales are off because auto sales are off; and replacement sales are down because motorists are driving less and radial tires are lasting twice as long as the bias-design tires of a few years ago.

Thus, because of the poor market, the tire companies have cut the price of their tires.

When auto sales improve, so will tire sales -- and prices can be expected to rise.

Even though tires have not changed much in outward appearance, they have changed internally to the point that owners should take time to see what the fine print on the sidewall of a tire says.

The reason: Tire companies have been under pressure to help automakers increase the fuel efficiency of new cars on the road. In so doing, tires have changed.Thse fuel-saving tires are also available on the replacement market.

One way of improving efficiency is to build a tire that can take a higher air pressure which reduces rolling resistance. If a radial tire is underinflated it can be permanently damaged and eventually lead to a blowout.

Tire companies in the last few years have undertaken a massive campaign to warn motorists of the importance of tire pressure, not only to increase fuel efficiency but also to prolong the life of the tire.