Smaller spare tire question/ 1960CJ5

I have 31 x 10.5 x R15 tires. The spare is a 15" rim but more like 28 or 29" tall.
The spare has to be replaced because of cracked sidewall.
Should I use a smaller spare that size with those other tires or go taller?
Any and all suggestions welcome, thank you.

 

Unless there is a space problem like 2 jerry cans and the spare not fitting the rack, I can see no reason why you would not want the spare to be the same size. If you have to use the spare and it is smaller, you will be putting unnecessary stress on the drive train because it will be covering less ground per revolution than the other 3 making it or the others have to slip to make up the difference. Sort of like driving in 4x4 mode on pavement.

 

IMO you have two options. Get a spare the same height as your road tires and use it as a spare only. Or get a 5th road tire and rotate all five tires regularly.

The main issue is to get a tire that's the same height as your road tires. This will allow you to put the spare on the ground at any location, and give you maximum flexibility. Running a smaller sized spare is not a good idea on a driven wheel, for any more than a few miles.

 

Reasons not to use a smaller or different height spare

1 steering - do much off a difference in size causes issues like the wheel not returning to center after a turn.
2 axles causes spider gears to be in constant motion ( open diff) Locking diffs, or Limited slips cause erratic behavior
3 braking this will cause "pulling" making it difficult to stop in a straight line.
4 some off the organized runs will not let a vehicle on unless the spare in 10-15% the size of the tires on your vehicle.

What you can do to save weight space is a narrower tire I have 33x12.5xr15 tires and use a 33x9.5r15 spare still have to be careful driving with a different size when its on the front but its much safer than a completely different size.

 

Thanks guys for your suggestions and advice on my spare tire question. I'm a firm believer when I say...ask Jeep people Jeep questions.
Thanks again.