I have 315 R75 16 tires on my truck right now, I was going to down size back to stock but was giving another full set of new tires of the same size. For the last few years I have had a full size spare tire in the bed, but I would like to put the original spare back under the bed to free up space in the bed. It looks like the spare is a 246 R75 16 (quite a bit smaller). So the question is IF i have to use the smaller spare, what are the drive ability concerns, should I the smaller spare be run on the rear only to minimize front end issues, how long would be "safe" to run the truck in such a manner?

 

Will be fine as long as you don't use 4 wheel drive with the smaller tire.

 

I've used my spare for the font before but if it was in the rear, I'd swap a front tire to the rear and put the spare up front. Somehow it's in my head that the drive axle shouldn't have two different sizes but not sure. Also, you may be able to get atleast a 265 under the bed. I tried but it didn't fit with my exhaust pipes so I went with 245 again.

 

If you have ANY type of limited slip/posi trac differential, running different diameter tires on the same drive axle will increase wear or finish off the differential if it's old. Handling issues are a whole nuther matter.

 

i have been told even if you don't have a limited slip it can cause an axle to fail. generally those spider gears all spin the exact same speed unless you are turning but i could see running a different size tire on 1 side of a rear axle cause the spider gears to move more than normal and cause an axle to prematurely fail. i know my dad blamed the axle in his 1 vehicle failing from running different size tires on the 1 side than the other. i have gone with it since. i will always runs same size tires on a rear axle.

 

Thanks for the input, so what I have gathered is that it would be best if a rear tire was lost to swap a front to the rear and put the undersized tire on the front and to not use 4x4.

Sure will be nice to have the bed back.

 

I have a full size 285-75-16 spare under my truck. I did let the air out of it to make it fit, but I do keep a small battery powered air compressor in the truck to add air if the spare tire is needed.

 

*Best* would be to have a same size spare. Barring that, if you need to use a spare, that's smaller, put it on the front, and EXPECT some oddities in handling. (and NO 4 wheel drive use please.)