Tires: Nissan Xterra 4X4 Tire Change, nissan xterra, viscous coupling

Question
My Xterra tires are 265/65 R17.  About 5 months ago, I replaced the front tires.  Now, it's time for the back tires.  These new tires are ridiculously expensive.  However, I have found some 265/70 R17 and came off a Suburban, they appear to have at least 20K more miles left on them, and are only $50 for the pair.  My question is this:  Will the different aspect ratios on the front and the back be acceptable since the difference is only 5?  That will add 1" to the overall diameter of the tire.  Or will the difference affect my vehicle negatively when I put it in 4-wheel drive?  I would save about $250 if I do it this way, but I don't want to mess up my transfer case.  Thanks for the help!

Answer
Paul,

The rule for 4X4's and All Wheel Drive is to ALWAYS have 4 identical tires - identical meaning same make, model, and state of wear.  To do otherwise is to risk damage to the drive train  - and in particular, the center unit.  This might be a transfer case or a viscous coupling.  Damage to these units is terribly expensive.

The reason is the difference in rolling diameter, which if significantly different front to rear, causes binding in these units.

So not only was it a bad idea to only replace 2 tires, it is an even worse idea to have different sizes front to rear.

You should consider yourself lucky to not have damaged the transfer case already.