Is it necessary to re-balance the tires every time they're rotated?

Dear Car Talk

Dear Car Talk | Oct 01, 1992

Dear Tom and Ray:

My dealer says my wheels must be re-balanced each time each time he rotates the tires. The tire manufacturer says the wheels should only be balanced when the tires are mounted or remounted. My dealer got a little huffy when I told him that, but he couldn't explain why. Who is right?

RAY: Gee, Hank, I'd get huffy too if someone caught me with my hand in the cookie jar. Your dealer's theory runs counter to Newton's First Law of Rotation: Tires in balance tend to stay in balance (that's Vinnie Newton, the mechanic, not Issac, the Physicist).

TOM: Rotating the tires doesn't affect the balance, because you're just moving the tires--rims and all--from one place on the car to another. And trust me on this, once the tires are balanced, they don't have any idea where they are.

RAY: But just to be sure, we always blind fold the tires when we move them around our shop.

TOM: Obviously, if you ever took a tire off a rim and re-mounted it on another rim, you'd have to balance it again.

RAY: Or if you hit a huge pothole, or drove into a curbstone, it's possible to knock a weight off the wheel and throw the balance off. But that's pretty rare.

TOM: By and large, tires stay balanced. And if the balance goes off for any reason, you'd probably know about it because the car would shimmy or vibrate, particularly at higher speeds.

RAY: Actually, I almost forgot the one legitimate reason for balancing tires every time you rotate them; kids in college. The dealer's kids, that is. It takes nearly 20,581 tire balancings to get a kid through MIT these days...and that's not including books and student activity fees!

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