You guys realize the OP is talking about a tire that is 1/4" or less different in radius, right?
Only 1/2 to 1/3 the difference between a new and wore out tire of the same size and model.
Steer axle, won't notice anything.
SRW drive axle, won't notice anything or cause any harm.
DRW axle, I'd make sure the smaller tire is at max pressure and maybe soften up the taller tire a bit if you're loaded pretty heavy, but I'd run it, maybe not indefinitely. I've put a new spare on the back of a dually with worn tires a few times. Didn't result in any problems.