Whew!  So many choices and what a headache.  Wanting to put 27" tires on my trail to gain just a bit more ground clearance without having to do clutch modifications.  Found a nice tire - Tusk Terrabites but in researching them it seems the actual physical diameter is smaller than the spec 27 diameter.  I asked the customer service agent how much smaller and she said it can vary from .5 to 1 inch!  Seems like if you are not careful you could buy a 27" tire the same size or smaller than the factory 26 tires.  I guess I'll need to get my builders square out and measure the factory CST Abuzz tires and see where my starting diameter is.  Unfortunately most tire manufacturers don't list any true diameters so buying mailorder may be a crapshoot.  Weight is another consideration.  I ride in Colorado's hard rocky terrain and kinda want an 8-ply rated DOT radial which the Terrabites are but they weigh in at 28.8 and 34.9 respectively for the 27x9x14 and the 27x11x14.  My brain is starting to hurt! 

[2015 Z Force 800 53/Trail EPS]

Whew!  So many choices and what a headache.  Wanting to put 27" tires on my trail to gain just a bit more ground clearance without having to do clutch modifications.  Found a nice tire - Tusk Terrabites but in researching them it seems the actual physical diameter is smaller than the spec 27 diameter.  I asked the customer service agent how much smaller and she said it can vary from .5 to 1 inch!  Seems like if you are not careful you could buy a 27" tire the same size or smaller than the factory 26 tires.  I guess I'll need to get my builders square out and measure the factory CST Abuzz tires and see where my starting diameter is.  Unfortunately most tire manufacturers don't list any true diameters so buying mailorder may be a crapshoot.  Weight is another consideration.  I ride in Colorado's hard rocky terrain and kinda want an 8-ply rated DOT radial which the Terrabites are but they weigh in at 28.8 and 34.9 respectively for the 27x9x14 and the 27x11x14.  My brain is starting to hurt! 

Yeah...it's a PITA for sure. No aftermarket tire will be as lite as the OEs so toss that out the window. And the reality is, they all have different ways to measure their tires but if you follow their methods, and put them all on a graph, they will be pretty close to what they say. Its just everyone puts them on either different width wheels or uses different air pressures. So, don't sweat that so much either. Get a tire that will get you through your rides, where you go, with no issues. For sure 27s or 28s, 8ply at least and really doesn't matter if it's a radial or not. I like a radial.. especially in snow, sand and on longer road runs but its not 100% necessary. Still...so many good tires out there to look at. I would pick three, read all the reviews I could stand, then pick one. No tire is going to be perfect but...any tire is going to be better then the OEs...IMO. My Abuzz failed me three times. That's all it took. My Grim Reapers never have...and so far no flats. But they have their drawbacks on SxSs especially on controlled power slides. And they are very directional. Good luck.   

Ok after watching tons of videos and reading lots of reviews I decided on the Tusk Terrabite tires in 27' diameter.  The Terrabites are a DOT rated, 8-ply radial tire.  These seem ideal for a narrow track machine such as the Trail model with their more rounded as opposed to squared off sidewall to tread transition.  There are quite a few RZR trail model reviews with this tire.  Probably not a good mud tire but most of the terrain I ride on is dry, hard and rocky.  I'm curious to see the final mounted diameter as some guys report they are smaller than the spec diameter but the tech at Rocky Mountain ATV said most tires are including the factory CST tires run smaller than spec.  The tires weigh in at 29lbs and 35lbs respectively for the 9" and 11" width; significantly heavier than the CSTs.  I'll post up a review once I get them installed on my machine.