OPINION

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

DEAR ROBERT: You don't have to do anything to protect your tires. 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 low 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.

DEAR CAR TALK: I hope you can help me finish a do-it-myself repair.

I took off an outer tie rod so I could replace it. Now the wheels won't stay straight. The car pulls to the right.

What do you suggest I do now?

-- Joseph

DEAR JOSEPH: Can you find a new route to work that only involves right turns?

This isn't an easy job to do on your own. Don't beat yourself up over it. We've learned a lot of tricks over the years.

One is that when we remove a tie rod, we always count the number of turns it takes to unscrew it. So, as we unscrew it, we're counting each revolution. Let's say it takes 13 turns before it comes out. When we put the new tie rod in, we turn it 13 times and then stop.

It still won't be perfectly aligned. In fact, it could be pretty far off, since aligning the front wheels requires real precision. But it won't be what you've got: Marty Feldman tires. Technically speaking, your "toe-in" is way off.

If we count the turns, we'll get the alignment close enough that we can drive the car to the alignment shop, then they'll do the fine tuning and get the alignment perfect.

My guess is you just eye-balled it, Joseph. You may have screwed it in too far or not far enough. Now you've got to get it to an alignment shop to fix your work.

If it's not drivable, you can do some more trial and error to see if you can line up the wheels. If you still have the old tie rod laying around, have a close look at it. Sometimes you'll see rust on the exposed part of the old tie rod, and by looking at how many threads are not rusty, you can see how far it was screwed in.

If you can't figure it out, or you've had enough trial and error for one lifetime, you'll just have to absorb the blow to your ego and have the car towed. But as long as you didn't screw up anything else in the front end, the alignment shop should be able to get the wheels pointing in the same direction. And hopefully, that direction is straight ahead.

Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting

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