Spare Tire Non-Matching

So I upgraded my tires from the stock (265/70/16) to 265/75/16, however I still have the stock spare. If I get a flat and need to use the spare, will it do any damage to my truck to run the smaller spare?

Also, will a 265/75/16 tire fit in the stock spare tire area without modification?

 

You'll be fine, I would say if there was a 1" difference in diameter between the spare and the other 3 tires it might be something to worry about, also I've crammed a 285 under there, I just used a sawzall to remove the "wing" thing / tab things under there and cut the exhaust so it wouldn't touch the tire.

 

You'll be alright, have you seen the size of the donuts on cars. 265/75/16 will be fine down there, no cutting.

 

Difference in diameter is 1.04" going from 265/70 to 265/75... but I don't think OP will have a problem if ya keep the speed reasonable.