Tires: tire size/compatibility, free tires, ford taurus


Question
I have read through information on this site and others you have recommended and am still sort of confused. One of my rear tires needs to be replaced. Do I need to get 2? I know it is generally recommended.
Also, a friend has some tires she is no longer using, assuming that the wear is ok, can I use them (they would be free!)? Also, the size is somewhat differed and I don't know if they are compatible. The factory size for my 96 Ford Taurus is P205/65/R15. The free tires are P195/65/R15.
Thanks in advance for your help!!

Answer
Kit,

First, the best situation is 4 identical tires - identical meaning same size, make, model, and state of wear.

For 4X4's and AWD's, this is a must as failure to do so may result in drivetrain damage - very expensive.

But for FWD and RWD, these rules can be relaxed a bit.  But tires should at least be identical as a pair on an axle.

It's still best to have all 4 the same, and the further away from "identical" the more likely your vehicle is to have emergency handling issues - just when you don't want any issues.

Size is a major change - and the one you've proposed has other issues.  It is smaller in load carrying capacity, and that increases the risk of a load related tire failure, which sometimes has tragic results.