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.
The tire sealant and inflator kit for the 2012-MY Chevrolet Silverado 1500. Photo Courtesy of PacePerformance.com
“The kit is useful, but in very limited ways, and then depending on how useful it is, you still might have to replace your tire,” Abram says. This is partially because not all sealants, such as aftermarket products, are compatible with the tire’s inner material — though manufacturer-supplied sealants will be compatible with your vehicle’s OEM tire.
Once the sealant is inserted into the tire, the tire must be fixed within a certain amount of miles. For GM’s product, that mark is 100 miles. The sealant must then be completely removed from the inside of the tire before the tire can be repaired. “The unfriendliness of dealing with the maintenance of a tire after a sealant has been expelled in there — it’s not a lot of fun,” Abram says. “So there’s a trade-off.”
In some cases, the sealant can be impossible to remove. That means a tire might still need to be replaced even if the original damage was minor. “There are proper repair procedures that the whole tire industry supports, and the sealants aren’t even close to that procedure,” says Bob Ulrich, editor of Modern Tire Dealer. “They are only a quick stop-gap to try to get you to where you need to go, and it can end up destroying the tire.”
Sealants vs. Run-flats
“A sealant kit will handle a lot of situations — except for sidewall damage and severe damage — but that’s where a run-flat tire stands out,” Abram says. “It gives you a little more flexibility in options when dealing with a more severe condition or a situation where you’re farther away from help.”
Run-flats can help the driver retain vehicular control during high-speed air loss. The tires can also handle sidewall damage and larger holes that kits might not be able to handle; thereby decreasing your chances of having to call for a tow.
The negatives? Run-flats cannot be repaired. Even the smallest puncture means you have to get the tire replaced, adding to the cost of an already expensive tire. And replacement availability can be problematic. But, Abram says these issues will decrease as more manufacturers make run-flats standard equipment, encouraging more tire manufacturers to enter the run-flat replacement market.
Run-flats vs. Traditional Tires
Run-flats include more material, making them heavier than traditional tires. For instance, an 18-inch Yokohama run-flat is 4 lbs. heavier than its traditional counterpart. While that doesn’t add up to the 40 lbs. saved by ditching the spare, it’s nearly half.
Some reviewers of run-flats criticize the rough ride. “That’s why run-flats haven’t caught on,” Ulrich says, adding cost and irreparability as other prohibitive factors.
Abram says that automakers have made design changes to vehicle suspensions to make up for ride stiffness. “A lot of the complaints about the run-flat tires are really not quite as legitimate as they might’ve been initially because vehicle manufacturers have altered their designs to accommodate,” he says.
And because a run-flat functions like any other tire, it needs regular maintenance too, including proper pressure and alignment. “Just because run-flats can operate under zero pressure to get you out of trouble doesn’t mean you can run over anything in the road and not have to worry about it,” Abram says. As well, because the vehicle’s tire pressure monitoring system (TPMS) is virtually the only way to tell your run-flat is losing pressure, it’s important that the system is functioning properly.
Weigh Your Needs
How are your vehicles used, and on what type of terrain? Answering these questions will help you decide if run-flats or inflator kits are right for your fleet — or if you should just keep the spare.
If you decide to lose the spare, make sure you have procedures in place for your drivers in case the sealant doesn’t work, for example, or if the TPMS says that a run-flat is operating at zero pressure. Be sure your drivers understand, for example, that after you use a sealant kit or a run-flat loses pressure, the tire is still only as good as a traditional spare: It has restricted driving capabilities and needs to be replaced as soon as possible.
It’s also OK to install traditional tires on a vehicle that came with run-flats, but you can’t put run-flats on vehicles not designed for them, according to Abram. If you change out the run-flats, be sure to protect yourself by either purchasing a spare or a sealant and inflator kit.
“The biggest recommendation I make about tires is do your research and get educated, because the tires are one of the most important things on your vehicle,” Abram says. “It should be a much a more intensive purchase than most people make it.”