Archive for Monday, March 1, 2004

Run-flats can help drivers weather damage from potholes

March 1, 2004


It was dark outside and Julie's voice sounded worried on the phone.

"Dad, I just had a blowout. Do I have one of those doughnut tire thingies?"

After a few seconds, I got the story: my teen daughter was driving three friends -- Jenny, Annie and Rachel -- south on Kasold Drive when they hit a massive pothole.

They had pulled off on 10th Street and were trying to figure out how to change the right front tire on her Focus in the dark.

"I'll be there in a few minutes," I said.

"No, that's OK. We've got it. I just wanted to let you know."

I felt a little proud of her -- my daughter was capable of handling a flat tire.

Only certain models

The next day, I popped the trunk of Julie's car and saw the Firestone tire's sidewall was completely ripped up the side.

I thought about getting her one of the new run-flat tires I had been reading about for a few years.

The run-flats are built to be able to drive for another 50 miles or so, which gives you a chance to get off a busy highway, without needing to change to a spare.

The tire shop guy laughed when I asked to buy a run-flat tire.

He explained that the manufacturers are building the true run-flats for only certain models of cars.

One of the first models to be factory-equipped with the run-flat tires was the Corvette, which has had them since the 1990s. Goodyear also makes them for the Plymouth Prowler, the Mini Cooper and the BMW.

Sealing it off

According to, there are three kinds of run-flat tires on the market.

One kind, self-sealing tires, is not a true run-flat, but it will handle nails.

Self-sealing tires can withstand a sudden puncture, because they have an inner lining that is coated with a sealant.

When the tire is punctured, the sealant immediately seeps around the foreign object, keeping the air pressure from dropping. When the foreign object is removed, the sealant immediately flows into the hole, keeping the air pressure from leaking out. Examples of such tires are Firestone's SEALIX, Uniroyal's Tiger Paw NailGard, and General Tire's Gen-Seal.


Another kind of run-flat tire is designed to stand up to a pothole blowout -- the self-supporting tire.

It features sturdy sidewall structure so that it won't collapse onto itself, even after it loses all air pressure.

Such tires need a special air-pressure monitoring system to let the driver know when the tire is blown.

Self-supporting tires include the Firestone Firehawk SZ50 EP RFT for the Chevrolet Covette C5. Other run-flat self-supporting tires are made by BF Goodrich, Dunlop and Michelin.

They are designed to allow you to continue to drive at 55 mph for about 50 miles.

Wave of the future

A third kind of run-flat tire are the auxiliary supported run-flat systems, according to These systems, which are expected to be widely adopted in the future, use a support ring attached to the wheel.

Michelin has been the biggest innovator, creating its "PAX System," which consists of four parts -- a tire, a wheel, a support ring and a tire-pressure monitor.

Even after losing all air pressure, the tire can operate at 55 mph for up to 125 miles. Since January 2002, the Pax System has been standard on the Renault Scenic.

Other vehicles with the system inslude the Audi A8, the Rolls-Royce Phantom and the Audi A6.

Michelin has partnered with Pirelli, Goodyear and Sumitoma Rubber Industries in developing the system.

Michelin announced last month that Nissan and Honda will use the Pax System for new 2005 models.

Not dead

I asked Julie later the specifics about her pothole blowout.

"So how did you end up changing your tire in the dark?" I asked.

A few houses down from where they pulled over, they saw a garage door open and the light was on. They found a man inside working on his car.

"Annie and I went over and we were like, 'Hi, do you think that we could borrow a flashlight.' And he said, 'Yeah, sure.' "

A few minutes later, he got them a light -- and also carried a floor jack and a jack stand over to the car for them.

"He pretty much did it all. All we did was hold the flashlight for him.And we brought the tire out of the trunk for him," Julie said. "I asked him if I could pay him. He said 'Yeah,' then laughed and said 'No.'"

Until the PAX system is available for all cars, I was glad to know that a few modern-day knights are practicing a system that's been around since the Middle Ages -- chivalry.

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