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tires February 05, 2018

Run Away From Run-Flats

Run-flat tires made their appearance over a decade ago. The concept is simple enough. On a conventional pneumatic tire, the weight of your vehicle is carried on a cushion of air contained in the tire under pressure. When a tire suffers a blowout or a catastrophic loss of pressure, the wheel or rim starts carrying the weight separated from the pavement by less than a quarter inch of rubber. The tire is quickly destroyed, and if the driver is crazy enough to keep going, the metal wheel is soon getting chewed up on the pavement, sending out showers of sparks. (Ever watch the pursuits in those reality cop shows?)

Many cars are now equipped with run-flat tires that use an extremely stiff thick rubber sidewall capable of supporting the weight of the vehicle, allowing the vehicle to continue to drive for a time in the event of a flat.

Another more complicated run-flat system uses a thick plastic band on the inside of the wheel to carry the weight if the tire loses pressure. It sounds like a good concept, except these are not some James Bond-type devices that allow a vehicle to defy gunfire and dragon’s teeth on the road, continuing a high speed escape unabated. A typical run allows you to drive a maximum of 50 miles, at a maximum speed of 50 miles an hour.

And then what? Limp to a local shop only to find that either the replacement tire has to be ordered, or their tire machine cannot accommodate the special run-flat rims? That’s assuming the 50-mile range will actually get you somewhere and you’re not stuck with your family camped by the roadside like some modern version of the Donner Party, casting lots for who gets eaten first.

Why would a car company do this to their customers? Because the C.A.F.E. (Corporate Average Fuel Economy) standards imposed by the federal government meant hefty fines if a car company’s fleet of vehicles did not meet the government mileage standard (averaged across the fleet), so manufacturers had to downsize their vehicles and engine sizes, but most of all, shave weight off while still leaving enough room for the passengers and their cargo.

When their efforts came up short a few pounds, their eyes inevitably fell on the spare tire, which, including jacking equipment, could total out at between 25 and 45 pound plus several square feet of cargo space, and seemed almost an anachronism in the age of steel-belted radial tires.

Thus began the war on the spare tire. The first step was the elimination of the full-size spare, replaced with the “donut” spare, a small skinny tire meant for temporary use at reduced speeds. When the weight/space crunch became too severe, this was discarded for the run-flat system.

I personally wouldn’t buy a car that used run-flats. Compromises mean a flat tire might cost me up to 24 hours of time to replace (picture a family vacation), plus the physical compromises to the tire itself, resulting in an often loud tire (road noise) and even worse, shortened tire life. So it’s an expensive tire – with poor characteristics – that wears out fast. That’s too many compromises for the ability to drive a short distance on a flat tire. On top of that, if the sidewall is damaged, then you’re not going anywhere anyway.

At the end of the day a car is about transportation. Getting where you’re going quickly and efficiently, whether it’s 10 miles or a thousand miles. It can be a matter of life and death. Anything that diminishes this ability is a negative.

My father was a very well-respected journalist in the automotive industry. He drove complimentary cars provided by the auto companies his entire life. One year he was driving a new BMW down from New York to the family Passover service in Virginia. Somewhere in Delaware the low-tire light came on. He stopped at the first service station. The people were very nice but couldn’t help him because the car had a run-flat system. He got the vice president of BMW North America on the phone. The BMW people were wonderful, guided him to the nearest dealer, and handled it as quickly as possible. But he was still two-and-a-half hours late. The presence of a spare tire of any kind would have allowed him to arrive on time.

Certain vehicles can’t carry a spare, such as performance vehicles that have different size tires in the front and rear. While I may question the wisdom of this arrangement, people who buy these generally know what they are getting, and are knowingly making a compromise.

But often people buy a late model used car only to discover the run-flat trap after they own it. Don’t yoube one of those people. Know what kind of tires you are getting on any vehicle you buy, new or used, and what provisions there are for a spare tire. Believe it or not, some car makers are simply giving you a can of “Fix-a-flat.” A prayer book would be more useful.

And as always, whatever kind of tire you have, we at Wiygul Automotive Clinic will always do our best to accommodate your needs.

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