Spare tire--going from 245 to 265

I'm getting new tires put on tomorrow, going from 245-75-16 to 265-75-16. I pulled an old 265 out of the barn to use as a spare, I'm just wondering is it really necessary to have installed as my spare? Would it be o.k. to just leave the smaller tire on the spare to use in case of an emergency?

 

No if you have a tire it is best to mount it as a spare. I mean it is not full time four wheel drive so technically you could do it but it could also tear up a diff as they will be rolling at different rates. If it is a pre-runner then just run it on the front and you will not have an issue but being IFS if it's a 4X4 I would swap it.