The numbers tell the story: Rotate the tires

Q Your article regarding tire rotation raised a question for which I have yet to find the answer. You stated that if the person had rotated their tires the "set" might have lasted 70,000 miles or more. I am assuming a "set" refers to the set of four tires on the vehicle, not just the front. I know it is a common theory that rotation will extend tire life but I cannot understand how it possibly can. Can you identify any independent studies that prove rotating tires adds to the life of a set of tires?

Your thoughts on the following: Assume rotating the tires would allow the tires to last 70,000 miles for the set of four. If the tires had not been rotated:

1. Assume the front tires last 45,000 miles.

2. Assume the rear tires would last 65,000 miles.

3. That is a total of 110,000 miles for the set of four.

It seems to me that the numbers say not to rotate. I suggest it is better not to rotate for the following reasons:

• Rotating masks an alignment problem.

• Rotated tires must wear into their new position. Wear is bad.

• Rotating tires brings more business to shops and sells more tires because they don't wear as long.

A Yes, I can identify an independent study that confirms tires will last longer if rotated on a periodic basis -- our '96 Tahoe delivered 73,000 miles from its original set of tires.

I appreciate the thoughtfulness of your commentary, but you've missed the absolute key point. Assuming the front tires last 45,000 miles and the rear tires last 65,000 miles does not mean the set of four tires lasts 110,000 miles.

The best way to look at the benefits of tire rotation is to compare tire replacement costs over the life of the vehicle. In the example above, by 65,000 miles the owner would have bought four new tires on the vehicle -- the front pair at 45,000 and the rear pair at 65,000. Following this "no-rotate" policy, he/she would be buying another pair of front tires at 90,000 miles, another rear pair at 130,000 miles, and the third set of front tires at 135,000 miles. A total of 10 replacement tires -- 2½ full sets -- would have been purchased and mounted at this point in the vehicle's life. By 180,000 miles, the front tires would have to be replaced again, and if the vehicle reached 195,000 miles and was still running, the rear tires would need replacement once again, for a total of 14 replacement tires -- 3½ complete sets -- over the life of the vehicle.

Had the tires been rotated regularly and lasted 70,000 miles for the complete set, at 130,000 miles the owner would still be riding on the first replacement set of four tires purchased and mounted on the vehicle. At 140,000, the second full replacement set would be installed, meaning a total of eight new tires in the life of the vehicle.

Tire rotation makes economic sense, not to mention allows the owner to keep well-matched tires on the vehicle at all times for optimal handling and braking. Most tire dealers offer free or very low cost rotation for the life of the tires, which provides a good opportunity to monitor wear on tires, brakes, shocks, suspension and steering.

Speaking of wear, remember that wear isn't "bad," wear is normal -- that's what happens to tires over their service life. The only bad wear is unusual or premature wear patterns that develop from alignment problems or by leaving a tire on one corner of the vehicle too long. Yes, tires do wear to the individual position on the vehicle, but of course that's precisely the reason to rotate them regularly -- so that this wear pattern doesn't become a permanent part of the tire's life. Once a tire develops an unusual wear pattern, that pattern determines the life of the tire. Rotating tires every 6,000 to 8,000 miles can prevent significant wear patterns from reducing tire life.

Said differently, rotating tires does not mask alignment problems, it prevents alignment issues from prematurely wearing out tires. Identifying an alignment issue at a routine tire rotation would allow the problem to be corrected before it destroyed the tires.

Does rotating tires help a dealer sell more tires? No, tire rotation helps tires deliver full mileage life. I'm sure tire dealers sell far more tires because of lack of rotation and premature wear than any other cause.

The bottom line? If you keep your vehicle for its full service life, do you want to buy at least three complete sets of replacement tires? Or just two, and save $250 to $500? And have well-matched tires on all four corners all the time? Clearly, the numbers say rotate the tires.