Guys,
There are 3 reasons to rotate tires:
1) To even out the wear rates, front to rear. This isn't much of a problem on a RWD as the wear rates are about the same, but on a FWD, the wear on the front is about 2 1/2 times faster than the rear - AND (to answer a question that wasn't asked!) it doesn't wear the tires out faster.
2) To even out the wear pattern. Steer tires tend to wear the shoulders and drive tires tend to wear the center. On FWD cars where the front do both steering and driving, this isn't much of a problem, unless there is some alignment problem. But on RWD, you can get as high as a 15% increase in tire life by rotating tires, because the tires are wearing on different parts of the tire in each position.
3) To make sure irregular wear doesn't become permanent. Tires with irregular wear tend to vibrate or cause noise (same thing, just different frequencies!) Each wheel position has a particular wear pattern and by rotating tires you prevent that pattern from becoming severe - because once it becomes severe, you can't get rid of it - short of shaving the tire.
So you can't rotate too often (other than the cost and the amount of labor involved!), but you can rotate too infrequently. My experience says that 20K is not frequent enough.
There are 3 reasons to rotate tires:
1) To even out the wear rates, front to rear. This isn't much of a problem on a RWD as the wear rates are about the same, but on a FWD, the wear on the front is about 2 1/2 times faster than the rear - AND (to answer a question that wasn't asked!) it doesn't wear the tires out faster.
2) To even out the wear pattern. Steer tires tend to wear the shoulders and drive tires tend to wear the center. On FWD cars where the front do both steering and driving, this isn't much of a problem, unless there is some alignment problem. But on RWD, you can get as high as a 15% increase in tire life by rotating tires, because the tires are wearing on different parts of the tire in each position.
3) To make sure irregular wear doesn't become permanent. Tires with irregular wear tend to vibrate or cause noise (same thing, just different frequencies!) Each wheel position has a particular wear pattern and by rotating tires you prevent that pattern from becoming severe - because once it becomes severe, you can't get rid of it - short of shaving the tire.
So you can't rotate too often (other than the cost and the amount of labor involved!), but you can rotate too infrequently. My experience says that 20K is not frequent enough.
