March 2012, Business Fleet - Cover Story
Where's My Spare Tire?
More manufacturers are turning to run-flat tires or giving buyers the option to replace the spare with a sealant and inflator kit. What’s the best option for your fleet?
In February, Yokohama released its newest run-flat, the AVID ENVigor ZPS (for “Zero Pressure System”). The tire is available in five sizes and is meant for vehicles such as the BMW 3 and 5 Series and the Mini Cooper. The tire uses a low heat-generating compound and sidewall reinforcement to support the weight of the vehicle during loss of air pressure, and was designed to help mitigate rideability and fuel economy issues.
Alternatives to spare tires are on the rise. More than 14% of 2011 models were equipped with a tire sealant and inflator kit instead, for example, and in 2006, that number was barely at 6%. The kits aren’t the only reason a new vehicle might not have a spare, though. Some manufacturers are choosing to make run-flat tires the standard option.
Run-flat tires were designed to allow drivers to stay on the road after a puncture and air pressure loss, usually at speeds up to 50 mph for no more than 50 miles. They were first geared as performance tires and are still largely used by luxury marques such as BMW, which installed them on almost all its 2011 models.
There are several technologies available, but the most common is a reinforced tire with self-supporting sidewalls, according to Bob Abram, product planning manager of Yokohama Tires’ consumer division. Abram says that run-flats were installed on almost 500,000 vehicles in 2011 and are expected to be on more than 650,000 vehicles within four to five years.
More manufacturers, however, are sticking with traditional tires but offering a sealant and inflator kit in place of a spare — either as an option or standard equipment (click here for a PDF of vehicles without a spare, listed by manufacturer).
A recent AAA study showed that by losing the spare tire and the tools that come with it, a vehicle’s curb weight is reduced by an average of 40 pounds. But what’s the risk in ditching the spare, and is it worth the reduced vehicle weight?
Fleet managers need to consider the pros and cons of the run-flats and kits to determine the best solution for your fleet’s needs.
Seal and Pump
Tire sealant and inflator kits come in various forms, from manufacturer-supplied kits to aftermarket products. More than half of new-model vehicles from General Motors have a kit included as standard equipment, according to Dave Cowger, GM’s engineering group manager for tire development.
The GM kit includes a compressor and sealant reserve. If a nail punctures a tire’s tread and the tire is losing air, the driver places the compressor on the tire’s air valve, releases the sealant, which covers the inside of the tire, and then uses the compressor to re-inflate the tire.
Cowger says the process takes about 15 minutes, and the kit works for about 80% of cases. It can only repair tread damage and not sidewall damage, and won’t work if the hole is larger than a quarter-inch in diameter. In such cases, the driver is left calling a tow truck or the manufacturer’s roadside assistance center.