my 96 ran stock, 225/75/15. i was looking for a good set of used tires that size for awhile. I came across 225/70/15 thinking ahh, not much difference it should be ok, then i started doing the calculators and couldnt believe the one number being different made a HUGE difference.

if he really has a 225/70/15 this is the specs.

sidewall 6.2
radius 13.7
diameter 27.4
circumference 86.1
Revs Per Mile 736

235/75/15

sidewall 16.9
radius 14.4
diameter 28.9
circumference 90.7
Revs Per Mile 698

the old tires will spin 38 more times in a single mile than the new tires... that oughta be fun on the transfer case.

calculations take from http://www.miata.net/garage/tirecalc.html

nice site for basic tire calculations