My question is two-fold:

1. My spare tire is smaller in diameter than the tires I have on my truck by quite a bit. I have 265/70/17 (31.8") diamter tires on the ground. If I have a flat on the rear will it hurt my limited slip rear-end to run the smaller spare tire short distance?

2. Will a 265/70/17 tire fit in the factory spare tire rack on the bottom of my truck (2006 F150)?

I ask this because I'm thinking about replacing my spare with a matching tire like I have on my truck.

 

i think up to a 35 can fit under there (i think)

i wouldnt drive very far with it on there, what i do is take a front tire and put it on the rear then put the spare on the front

 

X2. I'm not sure it would ruin the LS, but its a cheap fix to make sure.

 

x3

the LS will probably get damaged...another thing to consider is your exhaust. if you put an oversized tire under there, an aftermarket exhaust may not fit. It's cheaper and easier to just keep what you got. If a rear flat occurs, just swap a front tire and put the spare up front

 

A 265/70r17 will easily fit under there, no problem. Stock tires that fit the 18" wheels are even larger and fit quite well.

 

You can fit a 35 in the original spot, but if you have after market exhaust it might get in the way.

 

I'll echo what Tylus said, if you have a rear tire blow, put the spare on the front and use the front tire for the rear blown one. Different sizes on the rear will tear up your limited slip.