Tires: tire size, sized tires, wheel positions

Question
can i use 205/70R15 tires on back and 215/70R15 on front of a 2000 Buick century LTD?

Answer
Kris,

The best situation is to have identical tires in all 4 wheel positions - and identical means size, make, model, and state of wear.  That way the vehicle behaves as closely to the way the vehicle manufacturer designed it.  The further away you are from that, the more likely you are to have issues, especially emergency handling issues - just when you'd want the vehicle to be predictable.

At the very least, you want to have identical tires on the same axle.  Clearly, different sized tires is not one of those.

But having different sized tires on a drive axle is the worse possible thing you can do - as not only will there be handling issues, but you'll be un-necessarily activating the differential and at the very least, you'll be shortening the life of the diff.