I just wondered about this: During a vacation trip this year, I had a flat tire on a Sunday morning, left rear wheel. Of course, we were just about to move from one campsite to the next, about 300 miles.
Since my spare is a full size spare, same as the regular tires (245/75-17), I did not think much about it, put the spare on and went on our way. I did make sure that the spare was inflated correctly, of course.
About halfway down the 300 mile trip, my display said "service traction control system" or something to that extend, and the warning light came on. After turning the truck off and on again, the light was out, and never came on again.
What I am wondering now is how my LS diff liked (or disliked, LOL) that trip. I guess since the truck had about 7K miles on it, the tires were a little bit worn already. There was a visible difference in wear - I'd say maybe a millimeter (1/20th - 1/16th of an inch) less wear on the spare maybe?
The flat was fixed, and the original tire put back on the following day and 300 miles later.
So what do you all think? Could that do any damage? I personally doubt it, as a couple of psi could make the same small difference in diameter, probably. I am at 10K miles now, and have not noticed anything unusual. What did get me wondering though was that traction control light that came on once during that trip.
What's your opinion? Can a 0.25% difference in diameter from a one or two millimeter tire wear cause problems?

 

you are fine.

 

Thanks. I am pretty sure you are right. What threw me off a little is that "service traction control system" message. We were near the GVWR also at that time, with a 5K lbs trailer in tow. I guess that traction control is really sensitive ....

 

i'll add a couple thoughts here.

at work on my old 99 f150, i had a flat on the interstate but had oversized tires. as you said, of course it was the left rear.

that truck survived about 20 miles with a 235/70r16 on one side and a 245/75r16 on the other .... no harm done, but i did try to take it slow.

the BEST thing you can do, is to put your spare on the front then move the front tire to the rear. this will give you the best chance for even tread on the back ....... but it is a total PITA!

if there's any doubt, put a torque wrench to the rear diff and check the LS.

 

I have to wonder if the computer takes a reading from traction control, TPMS and any other system that comes in contact with the road so it can adjust itself. We know that the spare doesn't have a wheel sensor in it.

 

Thanks guys! I am not sure what the traction control warning complained about. But since it only ever happened once in the 10K miles I have on the truck now, and that was during those 300 miles towing with the spare, I think it probably was related

I have never heard of this. It's my first LS diff also. Meborder, what do you mean?

 

I'm not sure what the exact spec is for the LS in the newer trucks, but there is a break-away torque spec for the clutches inside the diff.

short version:

jack a wheel (block all others) and put trans in neutral. Put a torque wrench on the axle shaft and lean on the wrench until the LS breaks free. If it took more than XX ft-lbs to overcome the clutches, then it is good, if it took less than XX then it is worn out.

on the old 7.5's and 8.8's the breakaway torque was abserdly low ... something like 25 ft-lbs IIRC. they would usually hold close to 40 ft-lbs if they were working pretty good, though.

strictly speaking, the axle on the torque wrench needs to be on the centerline for the axle on the truck to get a good reading. realistically, i've always just used a lug nut. your reading will be "wrong" but will be close enough to know if you need to check into it any deeper.

i doubt your truck saw any ill effects from just a difference in tread, but this is a pretty easy way to reassure yourself.... cheap and easy