Tire size questions

I've just been given two used (about 60+% tread life remaining) P235/75R15 tires that will fit my Jeep's rims, right now I have P215/75R15s that are pretty warn out (20-30% life left), my Jeep is 4wd, and some one told me that I couldn't just put two tires on it, and they all need to be the same size, I can see how different sized tires could screw up the power transfer in the 4x4, but, what I was wondering is, if I put the 235s in the back, and say got new 215s or 205/60s for the front, could I drive my Jeep with out any serious handling or stability problems (tendency to roll over, ect.). I guess I could get by the summer with no 4x4 (I'm getting the body done PERFECT, so its not going off road for some time), and I probably won't be driving it till winter any ways (for winer I have 3 Studded tires with 80% life, and another older studded tire with about 50% and they're all 215/75R15s). Any help would be appreciated. Also, where is the spedometer cable, back or front, and how would I reset it to make up for bigger or smaller tires?

You could put the 235s on the rear and the 215s up front with very little impact on your driving. You might want to pull the front driveshaft just to prevent the thought of pulling the t-case lever although those *might* be close enough in size that you could still four-wheel on loose enough surfaces.

Speedometer cable connects to the output of the transfer case. Your fellow Aussie, gojeep, has a conversion writeup on his site but with 235 the change is so insignificant that I wouldn't bother.

I agree with Yucca-Man. You can do it, but remove the front driveshaft to be sure you don't forget and yank it into 4WD.

The speedo is probably not accurate with the stock tires anyway. The difference between 215/75s and 30x9.50s is only 6%, which translates into 3 MPH at a 50 MPH road speed. The 235 is slightly smaller than a 30, so you're looking at about a 4% or 5% difference. More than likely your speedo will be more accurate on 235s than it is now.