Wondering if you really need the exact size for a spare. Take for example the smaller donuts some cars have. I'm not talking a huge difference. Say if your spare was a 35 and you had 37s. I think you could still get home fine. Comments?

 

I don't KNOW but I'd guess having a smaller spare would play hell with the ESP. Since one tire would be turning slower than the other I'll bet it would see it as slippage and try to correct.

Jim

 

On smaller cars, it's not too big a deal since they're mostly on-road. But if you're out wheeling when a tire goes out, having the same size will come in handy [preferably, a matching spare]. Just not sure you'd want to trust a donut spare out on the trails. Just my

 

The reason you cannot use an odd size spare is the differential needs to turn both wheels the same speed. With a smaller spare, this is not possible because a smaller wheel will want to turn faster. This will damage your axles and differential and pretty much immobilize your jeep.
On a typical car, this is not a problem because you only have 2 wheel drive and you have a different type of differential.
I suppose if you had to, you could put a spare on the front and stay out of 4wd if you only had a small spare.
My advice is to get a full size spare and not have to worry about it.

 

The traveling difference while driving straight ahead for the two tires on the same axle would be over 6" per tire revolution. I think the differential would not like that. They already run very hot. I think you'd risk damaging it if you did this for very far. If you're in 4WD, then that tire rotational difference would be transmitted to the other differential as well (since a Jeep is essentially locked between the axles when in 4WD). So, you might have the pleasure of blowing two differentials in an out-of-the-way place.

I can also confirm that the ESP would be unhappy, but the stock function to turn it off (hold it for five seconds or whatever) would keep it from shutting off your accelerator and applying the brakes on one side of the vehicle (a scary thing to have happen if you're entering the Interstate when it goes into action).

Bottom line: You need a same size spare.

 

The spider gears don't normally turn when going in a straight line. Putting different size tires on each side of the diff will cause the spiders to spin. That will indeed cause more heat than normal.

Now put that in a limited slip and you have clutch wear too.

Flip on a locker to get out of a tight spot and you'll stand an even better chance of having an opportunity to upgrade axle parts.

So, if the goal is to wear out parts as quickly as possible so you can justify that Dana 60 swap, go with the BIGGEST spare diameter differential you can!

 

THAT WOULD BE A REAL BAD IDEA !!!!!!!!! Im an gm tech and i have seen
guys blow up diffs due to rotation being diffrent speeds

 

x2 on the diff issues mentioned above.

I'll add that if you off road, and you wanted 37's because the terrain was so tough that for example 35's would not make it....and, that terrain kills one of your GOOD 37's....can you even get back out on three 37's and some crappy spare?

 

For most cars with smaller spares, they specifically mention in the manual to only use the spare on non-drive wheels. If you blow a driven tire (ie - a front tire on a front wheel drive car), you're supposed to move a full-sized tire from the back to the front, then replace the rear with the spare.

 

If your on the trail and have to change tires just think what you want to get you home.