Wxboy - buddy not trying to be rude, but you are wrong. Think of this, why would the manufacturer (FORD) give you a spare to use that would prematurely ruin or wear out your rear diferential unit? Spare me the doom and gloom answer of them making work for themselves, you would not have a smaller spare if it was not ok to use. I know what I am talking about here, it is ok to run to difrent size tires on a limited slip rear diff because it a one wheel wonder. Traction only goes to the tire of least resistance, it is not putting power to both of your rear tires, just one. Like I said earlier a locker, or posi, detroit true track or track lock, (I'm not sure what the torsen rear end requires but I am guessing it is a full size spare because it's mechanics are similar to or the same as that of detroit true track), anyway not ok with those types of rear diffs, you need to run the same size spare as what is on the other side. For a short run on your spare to a shop to repair the original, you are not hurting anything on your limited slip. I'm not talking out of **** on this subject this is pretty common knowledge stuff here. Why not call your local Ford Dealership and ask them to explain this to you if you think I am trying to feed you a load of kaka. I do agree with you though that I think it would be better if we all had full sized spares with real tires on them and not some crappy donut.