On my 83 f150 4x4 5.8liter truck, I have tires sized 31x10.5x15. Can I put a different sized tire on my rims? If so, what size?

 

Yes you can change the tire size to whatever you wish, you may have to add some lift if you want to go bigger though.

 

I have to ask because I'm a little slow. I can keep the same rims and put a different size tire on them? I'm guessing as long as the new tire is 15 inches, then I'm good to go?

 

Yes and no.
Wheel sizes do determine what tires fit. Being a 31/10.50 im sure your rim is a minimum 7.5" wide.
A 7.5 rim is good for a 7"- a 10.5" wide tire although the wider the tire on a narrow rim means your sidewall will have more of a "belly".
If you went to a 31/13.50 bogger on a 7.5 rim you would probably roll the bead off.

Personally i try to keep my rim no more than 2" undersize the width of the tire. 1" is preferred by me.
Maybe you could tell us your sizes ( rim and wanted tire) and we could go from there.

 

My opinion,, the 31X10.50 tires are probably as big as you need to go on your stock rims...

Any larger and the rims aren't wide enough(in my opinion).

I have run the 31X10.50's for years on my 85 with no issues..

I don't (personally) have any need for larger tires and wheels because I don't want the expense or other complications of a lift kit,,suspension problems, etc..

Just food for thought...Trav..

 

I have ran 12.50's for years on 8" wheels with zero issues. IMO the 7.5" wheel is good for 11.50's and lower, and an 8" wheel is good up to 12.50's. I personally wouldn't go to a 10" wheel unless the tires were wider than 12.50. If you plan to wheel it at all yu can air down 12.50's very low on 8" wheels and not lose a bead. I have ran 35x12.50's on 8" wheels at 10 PSI with no issues on the trail, Don't try it on the pavement though.

 

XJ
The issue with a 12.5 tire on a 8" wheel is 2" of over hang sidewall to start with. Add vehicle weight that increases the "belly". My problem with that is its too easy to pinch the sidewall between truck and a rock or what have you. The more vertically inline the sidewall/rim are the more protection you have. I ran a 32/11.50 on a stock isuzu 15/7.5 rim and cut the sidewall on a curb in town. Again i completely understand and respect your opinion but with my experiences its just not sensible.