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Tire Talk: It is dangerous to install run-flat tires on older cars

It is against tire industry standards to mix run-flat and regular tires.

  • Mercedes-E5001

I bought a 2003 Mercedes E500 that needs two tires replaced on the rear. My front Bridgestones are OK, with 50-per-cent tread left.

I?d rather not buy a set of new tires for the back and be in the same situation later looking for two tires. I am thinking using a used set of tires and then wear them all down evenly.

I found tires on Kijiji that have 70-per-cent tread left, but they are run-flats. Can I use run-flat tires on one axle and regular tires on the other?

It is against tire industry standards to mix run-flat and regular tires. More importantly, the recommendation is that run-flats never be used on a vehicle that does not have a tire pressure monitoring system.

The second rule is kind of obvious: the run-flat does not show it has lost air pressure, so running at zero pressure, the tire can overheat and cause loss of control.

Run-flats are meant to be run only for short distances at reduced speeds when they are at zero pressure. At highway speeds, you won?t know the run-flats are flat until you experience a sudden, very dramatic, delamination as the tire comes apart.

The rule about mixing tires is a bit more subtle, but valid.

How the tires react under load, cornering or braking is part of the vehicle?s suspension design. The sidewall flex is taken into consideration when the suspension is set up by the factory engineers.

The issue is the run-flats have sidewalls that hardly compress at all. So they will react differently when cornering hard. Their contact patch will not be the same as the regular tires.

That makes for a car that will have different handling characteristics at opposite ends of the car. That can catch the driver unaware in an emergency manoeuvre.

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I drive a 2007 Buick Lucerne that has 44,000 km on it. Friends say the tires should be replaced because rubber has about a five- to six-year lifespan. Is this correct? There is little or no apparent tread wear.

Yes, your friends are correct. Your tires need to be replaced, regardless of tread depth or wear.

Tires need a certain amount of elasticity to get good grip. The oils and chemicals gradually dry out, whether the tire is driven or not. So, there is little grip left for emergency stops or rain grip.

Drivers are not really aware, because the grip loss is so gradual, you just compensate for it. Find an empty piece of road and try a full-out panic stop. The long distance will surprise you.

Send tire questions to: thetireguy_1@hotmail.com. Mail volume prevents personal replies.

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