Dear Tom and Ray:

I have a 2004 Hyundai Santa Fe with 47,000 miles on it. Recently it developed an unpleasant rumbling noise. After taking it to the service department, I was told that my tires are "cupped" and should be replaced. For a temporary fix, they rotated the front tires to the back. I still have the noise, but it's not as bad. And given a choice between living with the noise and paying for new tires, I'm thinking of living with the noise. The tires have plenty of tread. Are "cupped" tires safe to be traveling on? Also, what causes tires to cup?

-- Susan

TOM: Well, first of all, cupped tires are tires that appear to have little scoops taken out of them. They're also called "scalloped" tires -- like scalloped potatoes.

RAY: There are two main causes of cupping. One is an inadequate suspension system. If your shocks are worn out and the tires are literally bouncing up and down as you drive down the road, every time they come down, they get scuffed, and that leads to cupping.

TOM: So you might not like the idea of spending money on new tires, Susan. But you might need new tires AND new shocks.

RAY: The other cause of cupping, in our experience, is real cheap tires. For some reason, they seem to get cupped more often than better-quality rubber.

TOM: Unfortunately, it's really not safe to drive on cupped tires. They have indentations in them. So every time the tire rotates, there are high spots that aren't touching the road. That means you have less traction, and less ability to stop and turn.

RAY: If these are your original tires, it's probably time to replace them with a good-quality set (original tires on all but high-end cars are notoriously cheap). But have your mechanic check out your shocks first. They may be fine. But if they're not, you want to replace them too, before you cup another set of tires. Good luck.