Fighting the Fifth Wheel

One of Detroit's perennial peeves is the spare tire: it is infrequently used, adds weight, wastes space, and costs some $170 million a year. American Motors did away with it in one 1965-66 model -- only to get a flock of gripes. But the industry has not yet given up the fight on the fifth wheel. Later this month, Pontiac showrooms will have the sporty new Firebird, which has the same body shell as its G.M. cousin, the Chevrolet Camaro, but is four inches longer. The standard Fire bird is more powerful than the Camaro (165 h.p. as compared with 140 h.p., though both offer optional 325-h.p. engines), will cost "a little more" than Camaro's $2,466 and come equipped with an inflatable spare tire that will save enough trunk space for an extra Scotch cooler. Called the Space-Saver, the spare takes up half as much room as an ordinary tire, can be inflated when needed with a Freon gas can. Developed by B. F. Goodrich, the minispare is guaranteed to last 1,000 miles, will retail at $32.80. Goodrich is also working on a tire whose sidewalls, in the event of a puncture, will fold inward, leaving the tread to form a tight, flexible band around the wheel. Former Chrysler President William C. Newberg's entry may be the most novel of all. The device, called PosiTrac, is a steel rim fixed to the metal wheel inside an ordinary tire, capped with a thick rubber tread. In case of a blowout, the car can be rolled along on the inner rim at up to 30 m.p.h. Newberg claims that with Posi-Trac, which costs $80 a set, "nails, spikes, bullets, you name it, cannot stop the car insofar as tires are concerned." More conventional solutions are on the way. New polymers and other advances, says Dr. George F. Lanzl, Du Pont research di rector, will some day produce "ordinary tires that will make it an unnecessary precaution to carry a spare."

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