[...]The real point is, the tires have to match in circumference (within the tolerance). Even further, one should say "effective" or "rolling" circumference. Strictly speaking, they do not have to be replaced as a set. Circumference varies by brand and model, tread wear and inflation. [...]
The 99 forester 5MT I just bought has two different brands of tires (michelins on back, bridgestones in front). The tread depth is very close between them (maybe 2/32" more in the back).
What is freaking me out is that there's no way the circumference is within 1/4" and I don't think it would be even if the tires were all 4 new and of-a-kind because the front end is so much heavier. Also general variations in tire inflation and cargo load would easily overcome this miniscule tolerance. I just measured with a string (tires on the car) and got a circumference of 79" in front and 82" in back---12x the tolerance! PSI is 28.5 front/26.5 rear (sub spec is 29/26).
What should I do? Replace all four tires? I estimate they have 30k miles left on them... And what about the issue that even with new tires, the circumference is not going to be perfect? I'm not trying to beat a dead horse, here. If this has been covered adequately in another thread please be kind .
As far as symptoms go, the only time I notice anything is a brief feeling of "hesitation" when starting from a dead stop. It happens between 0-3 mph (my estimate) and I do get a sensation that power is moving front-back-front-back. It's all over in less than a second.