Car Talk: The wheels of modern vehicles stay round (and round)

Dear Car Talk:

If I leave my car sitting for two or three months, do I need to do anything to protect my tires other than perhaps inflate them to maximum recommended pressure?

Do modern tires develop flat spots? Thanks. — Robert

You don’t have to do anything to protect your tires, Robert. Inflating to the maximum allowable pressure, while not harmful, is not really going to help.

Modern tires can develop flat spots. But they’re temporary and will correct themselves quickly.

Here’s what happens: Beneath the tread on modern tires is a layer of nylon. When you drive, that nylon layer heats up along with the rest of the tire.

Then, when you park, there’s a spot where your tire meets the ground that is flatter than the rest of the tire. That’s known as the contact patch. Obviously, you need a substantial contact patch so you can steer and stop the car.

But when you park the car, the tires cool down. And when that nylon later cools down, it can stiffen up a bit and retain its shape.

So, the part of the nylon band that’s under the contact patch will sometimes “set” in that flatter position.

This is more likely to happen when outside temperatures are cold or when you leave the car sitting for a long time.

That’s your flat spot, Robert.

The good news is that it’s not permanent. As that nylon layer heats up again, it will quickly re-form itself to the shape of the round tire.

It may take 15 or 20 minutes of driving if the car has been sitting for a long time. And during that time, you may feel a mild vibration, as the flat spots come around and pass the ground.

But before long, it’ll take its normal shape again, and no permanent damage will be done to your tires.

If only the flat, shiny spot on the back of my head was so easy to get rid of, Robert.

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