TPMS UPDATE // No Spare, No Problem? spare tire is a way to shed up to 50 pounds. Generally, a 10 percent reduction in vehicle weight yields a 6 percent improvement in fuel economy – and spare tires and jacks are easy targets. Gaining a 10th of a mile per gallon in federal fuel economy tests is important in meeting ever-expanding CAFE standards. Those pounds and ounces may allow an automaker to reach 29.5 mpg on a vehicle – which can be rounded up to 30 mpg on the window sticker. The consumer benefits too; a 1 mpg difference in fuel efficiency may save more than $100 per year, according to the Department of Energy. If an owner drives 100,000 miles carrying around a spare tire they never use, it burns a lot of extra gasoline. Also, deleting the spare often provides more trunk space. The cost savings to auto manufacturers are substantial: eliminating the spare saves at least $20 per car. In the 2012 model year, approximately 15 percent of new cars came without spare tires. With the exception of pickups and SUVs likely to be driven off-road, the trend for most vehicles is to eliminate the spare. In most cases, a spare won’t even be offered as optional equipment – and there may not even be a place to put a spare. When tire failures do occur, drivers increasingly rely on roadside assistance services to take care of the problem. With help easily available through cell phones, many people simply choose not (or don’t know how) to deal with flat tires – even if they have a spare. Drivers may still fear being stranded, but the almost universal use of cell phones has made that much less likely – whether or not they have a spare. So how is the owner of a nospare car supposed to deal with a flat? No matter if the car has runflats or fix-a-flat, the owner must obey their TPMS system and either re-inflate or repair the flat. If they 54
September 2013 | Counterman
choose to ignore the problem, they will definitely be stranded. Many expensive cars are opting for run-flat tires, which can be driven at moderate speeds for 50 miles or so with a puncture. The reinforcement built into run-flats supports the weight of the car and is designed to allow a driver to find a safe spot to stop, rather than being stranded in an unsafe place or on the side of a highway. But, since run-flats are limited to 50 miles after they lose air pressure, if a motorist is too far from civilization, they may not help much.
Flat-Fixing Kits As an alternative, many OEMs are replacing spare tires with “mobility kits” designed to fix most flats. These consist of a can of sealant that is injected through the valve stem to plug the puncture, and a small electric compressor to reinflate the tire. Tire mobility kits typically weigh less than six pounds, compared to 30 for a temporary spare and 50 or more pounds for a full-size spare. Unfortunately, they, too, have drawbacks. The kits generally only work on punctures of 1/4-inch or less in the tread or shoulder areas of the tire. Blowouts, cuts, cracks and sidewall damage that potholes frequently inflict on low-profile tires cannot be repaired by the kits. OEM sealants are typically approved for use with TPMS sensors. But, longterm exposure can lead to damage. Using these kits is pretty simple: plug the unit into a 12-volt power outlet (cigarette lighter), and con-