Is using a “mini-spare” tire on a rear-drive axle causing the differential gears to wear excessevley by rolling one side at a much different speed (due to size) than the other,like turning left tuns at 70MPH for the last 40-50 miles?
Theoretically, the mini-spare is only narrower than the regular tires, not shorter. So the circumferences should be the same and the differential shouldn’t know the difference.
Of course if you’re running a non-stock tire size this probably isn’t the case, and some cars (such as Subarus) are sensitive enough that the difference in circumference due the the regular tires being more worn than the mini-spare can cause problems.
If you have a limited slip differential or a locker there’s a fair chance you could damage it.
For 40-50 miles?
Take a look at the information on the sidewall of that Temporal Spare tire, and also the information in your Owner’s Manual regarding the spare.
More than likely, you will see warnings about not exceeding 50 mph with the spare.
There may also be information about how many miles can be driven on that tire.
That little spare is only designed to allow you to get to a tire store for repair/replacement of the punctured tire.
Do you really live 40-50 miles from a tire dealer?
Yes, you could have caused damage to your differential, but frankly, I think that you are very lucky to have not had a high-speed blowout on a tire that is not intended for high-speed driving.
The mini spare is usually called the 60/60 tire; it should not be driven further than 60 miles and not faster than 60 mph. And the pressure has to right up to that specified; this time ON THE TIRE, mine say 60 psi!
I would be extemely careful with SUBARU running a mini spare, and disconnect the AWD system by inserting a fuse, as outlined in the owner’s manua.
I once had a rear drive Chevy with positraction, and it warned to only drive with the mini spare a very short distance.
why in the world are you doing this? Get a real tire. That sad excuse for a spare is not intended for any kind of speed or distance, but just to get you to a place you can buy a good tire. That amount of driving will not affect anything else on your truck. Once you get to a tire store, buy a new rim and tire for your spare, and find a welder to put a tire rack on the tail gate. Or I guess you could just get a plastic Jesus for your dash.
I’m surprised you’re able to drive that fast on the doughnut. I had to put my mini-spare on my civic one time, and even the 5 mile trip to the tire store was a pain. I couldn’t go much over 40mph without feeling the back end swaying back and forth