I have 265/70/17 BFG At's (not the new design), I cant remember the make of my spare that came with the truck, but its the same size.

I unmounted it from under the truck to clean the frame up a bit and it just looked bigger. Sure enough, putting it next to the BFGs, it is noticeably larger in diameter. Even accounting for the fact that theres no load on it.

I have read somewhere that the BFG ATs (not sure about the new model) run a little small for their size, which seems crazy.

Anyway, no big deal. I'm not concerned other than what happens when I need to use the spare.

The truck has 4wd and a LSD. If I got a flat on the rear end, should I put one of the front BFGs on the rear and put the spare on the front end? Is it ok to run slightly different diameter on the front end just to get it home/fixed?

I'm guessing the best thing to do would be to get a used BFG and mount it on my spare?

Thanks for reading

 

Just put the spare on and get the flat fixed asap. Driving on it temporarily won't cause any harm.
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A set of tires with 30,000-40,000 miles on them are roughly 1 size smaller than when they were new. If the spare was still new compared to well worn tires it wouldn't be unusual.

 

Thanks for the replies guys. I guess I worry too much about stuff.

That makes sense, my BFGs have ~40k on them now. Though it looks like they have another 15-20k in them no problem. Couldn't be happier with them. I may still just look around for a used one that someone is swapping for new ones so I have all 5 matching

 

You'll be fine with that size difference on an LSD temporarily. A locked differential though? That's when you'll start running into trouble.