Does bad alignment cause tires to "cup"?

Dear Car Talk

Dear Car Talk | Sep 01, 2002

Dear Tom and Ray:

I have a '98 Honda Civic with 73,000 miles. Over the past month, I've noticed that my car seems to bounce excessively when I'm driving over bumps. Also, when I am accelerating or braking quickly on a bumpy surface, the wheels seem to skip over the ground (I can hear the rubber squeal as the tires lose and gain traction). I took it to the dealership, and the guy told me it was an alignment problem that caused "cupping" on my tires and a bumpy ride. However, the ride is smooth on a smooth road. It's only on bumps that I have problems. -- Phil

TOM: Gee, I'm confused, Phil. When you described your symptoms, my first thought was "shocks." But the reaction of the dealer confuses me.

RAY: Right. How he could EVER miss an opportunity to sell a set of shocks is absolutely beyond me!

TOM: Actually, the first thing you should check is your tire pressure, Phil. Because overinflated tires can cause exactly the symptoms you describe.

RAY: But if the pressure is correct, then I think your problem IS shocks (also called struts). Simply put, the job of the shocks is to "push down" and keep the tires firmly planted on the road, no matter what bumps they encounter. When the shocks wear out, the tires bounce over bumps and then stay in the air.

TOM: And when tires bounce, they do exactly what you describe. They make the car bounce, and they chirp when you brake on a bumpy surface, because they're skidding every time they come down and make contact with the road.

RAY: Now, it's possible that your bad shocks have also cupped your tires. "Cupping" is when there are scoops of rubber worn out of the tire tread. That tends to happen when your shocks are bad, because every time the tires bounce up and come down, a different part of the tread gets scuffed. So if your tires are already bad, just replacing the shocks won't solve the problem. You'll have to do both.

TOM: But bad alignment doesn't cause cupping. Nor does it cause the handling problem you describe. So I'm not sure what the dealer was thinking. We'll have to look into this. And if the Mechanics' Boat Owners' Association finds that this guy failed to even attempt to sell you a set of shocks, he might face severe disciplinary action.

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