QuestionBarry:
My wife is of the opinion that when it's time to buy tires, we should only buy two tires at one time (i.e. rotate the purchases to save $). We have both AWD and 2-wheel drive (front drive) vehicles. What would you do?
I've tried to tell her that since I've always purchased 4 tires at one time, the tires all wear out at the same time and all need to be replaced.
Let's say that this was not the case and only two tires really needed replacement. What should we do for our A) AWD Subaru SVX and our B) 2-wheel drive Volvo 850?
AnswerAWD vehicles, particularly Subarus, need to have all four tires within a reasonable diameter range in order to prevent the center diferetial from wearing out. As these are pretty expensive to replace, I would make sure all four tires are rotated regularly and wear out at the same time.
While there isn't a mechanical reason to rotate tires on a FWD, there are some safety as well as aesthetic reasons to rotate tires regularly.
If a tire is not rotated regularly it can develop a wear pattern that is unique to that wheel position - front tires on a FWD steer, brake, accelerate, and carry most of the load while the rears seem to be along for the ride. Sometimes these wear patterns will be uneven and irregular, which can lead to premature wear out (say the shoulders of the tread only) and noise or a vibration.
I have estimated that if tires are rotated regularly, you can actually get up to 15% more life out of them, simply by having the tires wear evenly.
Now the safety part. As tires near wearout, they will be more likely to hydroplane, and if the worn tires are on the rear, a spin out is much more likely. If the front and rear tires are at different states of wear (and even if they are just different designs) the vehicle might handle a bit funny in emergency maneuvers - just when you'd want them to be predictable.
So overall it's best to rotate regularly and before the hydroplaning situation becomes a problem, replace them - all 4. This is what I do.
