Spare tires can keep carmakers up at night. Big tonnage vehicles — like trucks — need full-size spares. For cars, however, fuel saving weight reduction solutions have helped toward the goal of removing extra weight-bearing mass.
Since the fuel crisis in the 1970s, carmakers have been desperately seeking higher fuel economy. Remove the spare tire and you instantly lighten the vehicle 70 to 80 pounds and create more trunk space. The tempa spare, or donut, came out of that fuel crisis.
The donut is the primary solution. The other option is a compressor-like device that seals and inflates the tire called an inflation kit. Other vehicles — until now mostly luxury vehicles — are equipped with run flats.
“It saved weight and trunk space, but with a donut, you still have to stop on the side of the road, the tire can be difficult to handle,” says Bridgestone’s Kurt Berger, manager, consumer products engineering, who has been with Bridgestone 23 years in research and development, quality systems and engineering.
Berger notes that when the donut was launched, it met a lot of consumer resistance. But then — unbelievably — customers began using it as a full tire in their maintenance program, rotating it with the other four tires. The donut is intended for short distance driving only, not as a replacement tire.
In the mid 1980s, run flats came to market. They’ve not been well accepted by manufacturers or consumers, even though you can still drive 50 miles on a run flat that has lost air.
“The downside,” says Jim Smith, editor of Tire Review, “and the reason manufacturers have resisted them, is cost. Even today the cost factor is at least 50 percent over the cost of a standard tires. OEMs are trying everything they can to get their sticker costs down.”
My tire karma has been off in the past couple of years. I have had three “air loss” events — the polite term for that fragrant rubber-burning blow out that sidelines your direction on the road (usually in the middle of the night).
“We don’t get flat tires like we used to,” says Smith, who has not been on a road trip with me. Smith says the industry has not done a good job of selling run flats and when consumers look at replacement tires they realize how much more they cost.
“When you lose air rapidly with a run-flat, says Bridgestone’s Berger, “you may not even be able to detect it. In fact, the new tire-pressure gauges, standard on every vehicle sold in America, emanated out of the run flat because it told you, you were losing air.”
Bridgestone is about to launch a third generation run-flat that closes the cost gap by about 15 percent and addresses the other big complaint about run flat tires — the hard ride.
“We’ve engineered out a lot of the shortcomings using special rubber polymers so that we can give the aftermarket a tire option that is affordable and comes with a mileage warranty, says Berger.
“Run-flats are still in the single digits for the overall market, says Dean Weeks, OEM technical marketing for Michelin. “Our forecasting says that the trend, while increasing, will not jump in the next five years. It is still less than 10 percent.”
The less costly emergency spare is the inflator kit. “Kits started coming on the radar in about 2007,” says Weeks. “Kits are edging up but we will see them level off by 2012 to about 15 percent of the market.”
General Motors uses inflator kits as standard equipment for weight savings/fuel economy in many of their vehicles. “We have had good experience with this in other global markets,” says Pam Flores a spokesperson for GM. “For some GM vehicles that come with inflator kits, a full-size or mini spare tire can be ordered as an option with the vehicle.”
Nissan, Ford, Chrysler and Toyota use full-size spare tires on some models, donuts on others and run flats in some models. — Kate McLeod, Motor Matters
Manufacturer photo: Full-size trucks, such as the Hummer, are equipped with full-size spare tires. When it comes to designing, engineering and validating tire systems, GM follows an extremely rigorous and comprehensive process. GM’s tire and wheel engineers develop GM-exclusive Tire Performance Criteria (TPC) specifications for each vehicle engineered in North America.
Copyright, AutoWriters Associates Inc., 2011