Run Flat Tires: How They Work And What's Good And Bad

August 24, 2010

It only takes one flat tire horror experience to make you regularly check your tires. My nightmare on the interstate came on an on ramp in a driving downpour. It was in pre-cell phone days (although I probably would not have called for roadside assistance anyway) and required setting up the jack and accessing a spare which was stowed under the vehicle. I can’t think of worse circumstances unless it would be more severe weather or that I had no spare at all.

Even being a vigilant observer of your tires will not ensure that you won’t end up on the side of the road with a flat. There is only one innovation that will eliminate the need for a spare tire and that’s a run flat tire. In fact, cars equipped with run flat tires are sold with no spare tires.

The run flat tire is designed to go 50 miles at a speed of 55 mph.

So how do these tires sustain highway speeds while being compromised by a puncture? There are three versions of the run flat tire.

The self sealing run flat will repair an intrusion in the tread area up to 3/16 of an inch. The inside of the tire looks like heavy duty fly paper constructed of about a quarter of an inch of black goo that serves as the tire technician. If the tire doesn’t self seal, the symptoms will be the same as conventional flat tire and it will need to be replaced.

The self-supporting run flat tire has a beefed up construction that allows it to carry the weight of the vehicle even though the tire has lost pressure. The use of a Tire Pressure Monitoring System (TPMS) is mandatory with this type of run flat, because without it the driver would not know that anything was amiss. The added strength of the self-supporting run flat comes from a reinforced sidewall and a bead that is designed so it will not separate from the rim.

The third type of run flat uses an additional level of support to take the load off the tire when tire pressure is lost. In this system a support ring is attached to the wheel and it supports the weight of the vehicle. This type of run flat allows for a better ride than the self-supporting system because the sidewall does not have to be as stiff since it doesn’t do the heavy lifting required of the self-supporting tire.

Consumer Reports’ reviews make mention of the stiff ride and also the higher cost of run flat tires. In addition reduced tread life is an issue. Toyota Sienna AWD owners have reported needing to replace their run flat tires after only 15,000 miles at a cost of $800.

While it may be true that changing a tire in the rain may be traumatic, replacing expensive tires every 15,000 miles may be just as memorable.

[Tire Rack]             

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