....your spare should be the same size as the rest or your tires?

How many miles can you drive with mismatched spare? Max speed?

What exactly happens when you drive like this, will your differential will be ruined?

 

#1.The tire that is smaller will rotate more than the others.
#2.As many as you want if you put the off tire in the front and don't use 4wd.
#3.It will mess up you'r transfer case if you drive in 4wd with different size tires.
Someone can correct me if I'm wrong,Please do!

 

Your right.
The different size tire is not a big issue in two wheel drive. If you have a posi-trac, or a locker it will be hard on it. The small spare is only meant to get you to the local shop to get it regular tire replaced/fixed.

 

On a related note.

"Worst place to keep a spare tire competition" Grand Champion

 

That is quite normal on older european cars to have the spare in the engine bay, some old VW beetle had a small line connected to the inflation nozzle to power the windshield washer.

 

If you get a flat on the rear and have a locker you'll have to swap a full size from the front to the rear to avoid damage to the locker. That's a headache with just one jack... I've also heard mismatched sizes can destroy a clutch style positration unit in short order.

 

i dont think you would damage the locker you would just have a squeeling tire when you try to drive down the road after the locker locks up and the jeep tries to turn towards the side that the spare is on.

if your open in the rear diff you can drive for a while on it with no problems. i had to do that when i was 16 for a while...