I would be more worried about the transfer case if you are in locked 4-wheel high or low, than the differentials.

Years ago we blew up (completely wrecked) a transfer case in a Jeep Grand Wagoneer while off roading due to the use of a spare with a smaller tire (about 1-1.5 inches smaller in diameter).

Spend a little $$ and get the same size spare. It's cheaper than a transfer case or differential

 

Not sure how this thread turned the way it did. I'm sure I'd be fine driving a short distance with the 265 spare, maybe a mile or two. I know how open diffs work and while I realize a 265 and a 285 are pretty close, I don't know how much extra wear and tear would put on the parts. I suppose you could compare it to driving in circles all day, but that wouldn't be the same as a smaller tire when it comes to the TC. I don't know if the smaller tire would cause traction control to engage. I doubt it, but I don't know if anyone here has a definitive answer, mostly just (educated) guesses.

As I said from the start (and in another thread) I plan to pick up a 285/75/16 spare tire. I'm hoping to get a used one as a free swap for the smaller spare tire, but if not I'll go buy one.

I'll give the tire shop a couple weeks to get a decent used one in on a trade. Leaving for HI in the morning, be there for a week, and not much driving through the holidays, so not a huge rush.

 

unless in locked mode the xsfer case is open diff right?

 

There is slip built into the transfer case, but not more than is necessary for the wheelbase of the vehicle. For example, while turning right, the left front tire will be turning much faster than the right rear. So there has to be an amount of slip built into the vehicle. But, there are limitations. Vehicles are not built to be driven in circles, except in Nascar. How many pieces in the transfer case are phenolic or plastic? Ask a trans shop guy. The trucks come with a full size spare because it is all wheel drive. Some all wheel drive vehicles will exibit a very bad shudder with new tires on front and worn tires on rear. Keep the all tires the same. The tire industry watch dogs don't even suggest only replacing 2 tires on an all wheel drive vehicle. All tires must "match." Dealers are far from tire experts. Most dealers know very little about tires. Bottom line is the tires are the most important thing on a car. You can have the best brakes, most horsepower, and most responsive suspension, but it doesn't mean a thing if the tires can't perform.