New here. I have a 2001 yamaha kodiak that I am putting new tires on. I put new moose switchback tires on the front. The rear tires I can get are also switchbacks as well, but they are 26x11x12 instead of the OEM 25x11x12. Am I setting myself up for problems

 

Don't see an issue. I have a '98 Big Bear with 26x10x12. Fits great.

 

You shouldn't do it. The outside size of the tyre determines how far the bike travels per rev of the wheel so, when in 4WD, front wheels will be moving 1.5 inches less per rev than the back ones, this can't happen, so the tyres have to slip or it winds the transmission up like a spring. On concrete or asphalt the transmission takes a pounding.

 

I just realized he was talking about running 2 different tire sizes. Yeah that's essentially changing your gear ratio on one and not the other.