I have 28x12.5 all around on my 99 500 ac . just make sure you add some spacers it will add stabilaty and shouldn,t have a problem .A word off advice don,t forget the lift kit.[img]i/expressions/face-icon-small-cool.gif[/img]

 

I put 27-12-12 rear and 27-10-12 on the front (dirt devils) this is only due to the rim width and I have no problems. As far as different tire size , this referances the fact that some manufactors put diffeent height tire on the front and rear of some quads and they have to increase in height equally; example if you have 25-12-12 rear and 23-10-12 front you would go to 27-12-12 rear and 25-10-12 front a increase of 2" all around. so you wouldn't effect the gearing in the front differental and all tires would pull equal.[img]i/expressions/face-icon-small-cool.gif[/img]