Can you replace a R255 tire with a R265?

Can you replace a R255 tire with a R265?
Yes, that's really not much if a difference. As long as the cross section (60, 65 or 70) is the same on both, that'll work. You should not, for instance, substitute a 265/60 for a 255/70, but as long as the cross-section # is same you're OK.

Some more information. As an example if you switch from a 255/70-15 to a 265/70-15 your speedometer will read 58.8 at a true 60 mph. Overall diameter will increase .55" which will cause a very slight loss of power. You would have to switch to a 275/65-15 to keep all aspects close to the OEM tire. it does make a difference when you switch tire sizes. My advice is to stick with the size tire the engineers chose for your vehicle. There is no positives to changing the size but there are negatives.