I have been looking to get some new tires for one of our Polaris Rangers, 900 XP. It currently has the factory tires, which I believe were Carlisle 489 AT.

As I look at some different websites, I have a hard time finding a big selection in the current sizes. The current tires are 25x10-12 up front and 25x11-12 in back. Is it OK to go to 26 inch tires? Seems to be many more to chose from if you go up in size. Any other suggestions for specific tires welcome.

Going up to 26” is fine. An extra half inch of ground clearance and not enough size difference to affect gearing or power.

26's is no problem on that machine. We have moved up to 26's on machines with less engine and there's not that much difference in power, provided you stick with something lighter than the gnarly, super-mudder style tires. The MudLite and SwampLite tires have worked well for us. The Bighorns seem to be a good option if wanted something a bit more all-terrain in nature.

How about going from 11 to 12 inches wide? Seems like I can find more in the 26x12-12 for the rear than the 11 inchers

So long as you have enough clearance to the inside and don't mind kicking up a little more mud on the outside, no problem.

I have a Polaris Razor 800. I went from 25's to 26's with no problem at all. I gained about 1" but part of that was going from worn tires to new treads.

My Teryx came with 27's......

went to 28-10x14's on all four corners.....no prob

good source

https://www.pureoffroad.com/atv-tires.htm

Another good source: ROCKY MTN ATV

here too

https://www.discounttiredirect.com/buy-tires/sti-chicane-rx-atv

You should have no issues going up in size but I wouldn't go any bigger than 27", you'll start breaking stuff if you do. I run 27" Mud Bugs on my Rhino but I also have a 2" lift on it, been running them for about 2 years now and have been stuck only twice. Most people generally run 12" in the back and 10" in the front.

Thanks!