I bet you can as well 28's verses 26's only puts the tire one inch closer to any point where it may rub and if the isn't anymore clearance then that they definetely missed the mark because there aren't very many machines that won't allow 28's stock
27 Big Horns on mine. The belt life should still be around 8,000 miles and with clean air the grease will stay clean enough. This will be a very fast UTV on the tight trails with the speeds under 50. Also a very good rock crawler. The high speed guys really need the super long 4 seater wheelbase for the speeds above 50 but those $22,000 + UTV's won't do well on the tight trails. I'm too old for the super fast stuff and there is a lot of fun to be had by backing it in on the 10 to 15 mph corners and keeping it sideways half way down the straight before backing it in on the next corner. We have lots of truck trail and sand wash for this kind of riding. Its a lot safer at speeds under 50 too. I will remove the sway bar for better suspension and install alloy wheels with more off set.
Talked to my yamaha guy yesterday about this very subject. I was looking for more ground clearance. Being a performance guy myself I understood his reply when he answered keep it @ 26. The weight difference is pretty significant. The horsepower needed to move the additional rotating mass takes away from the design intention . This machine is built to benefit being light and nimble rather than relying on brute force.
If/when I get one, I will try to stuff the biggest dang tires I can under there! lol, well ok maybe not quite like that. But I will definitely put larger tires on as we are big time rock crawlers. Not only that but I totally dig the look of the RSpec with larger tires rather than the stockers
P.S. I have no idea what those tires in the photoshopped picture are equivalent to. I just dropped them in and sized to my liking lol!