Dear Tom and Ray:

I have a 2003 Nissan Maxima that my wife took to the dealer for a 7,500-mile checkup. The mechanic changed the oil, rotated the tires and balanced the wheels. My question is: Is it necessary to rebalance the wheels each time you rotate the tires? His explanation to my wife was that the tires would be in new locations on the car, and should therefore be rebalanced, since customers have complained of shimmying at high speed. I always thought that once a wheel is balanced, it doesn't matter where on the car it sits. Your input would be most appreciated. -- John

TOM: Well, in theory, you're absolutely right, John. Once you balance a tire, the tire couldn't care less where it goes. You can put it in the front, the back, or hang it from a tree in the back yard, and it should still be balanced.

RAY: However, sometimes tires can get "unbalanced" over time. Wear and tear can throw off the balance, or a weight can get knocked off when you hit a pothole or run down your mother-in-law. And here's the tricky part: If you have a slightly unbalanced tire on the back, you probably won't notice it. But if it gets moved to the front, you could notice a shimmy at high speed.

TOM: Why? Well, you're simply more sensitive to what's going on in the front, because what happens to the front wheels is telegraphed right up the steering wheel and into your hands. And we've had enough customers come back to complain of shimmies that we always check the balance now when we rotate tires.

RAY: But that's where we differ from your dealer -- we CHECK THEM first, before we go ahead and balance them. In our shop, I always have my guys put the tires on the balancing machine and check them before taking all of the weights off and starting over. If they're balanced, fine, on they go. If they're not balanced, sometimes just adding a weight will fix them. If that's not possible, then I tell my guys to remove all of the weights and do a full tire balance.

TOM: And a lot of times, we check and none of the tires needs rebalancing. Sometimes one or two need it. Sometimes all four. But we do it on a tire-by-tire basis. What your dealership does is take all of the weights off first, assuming all the tires are unbalanced. To me, that's extra work, and it's extra cost to you.

RAY: So your guy is right to be concerned about tire balance when rotating the tires, because customers do complain about shimmying. A good repair shop will anticipate problems like this and head them off before it gives you back your car. But if he was interested in saving you some money, he could check them first and only balance those tires that needed balancing. And then make his extra money selling air fresheners, like the rest of us.