When it comes to tire selection it depends on the type of riding you do. The make of tire is only preference, if you do trails I'd be sure to get a tire that is 6ply, anything else you risk punctures. Rears I'd go with 20-10 or 11-9 fronts stick with 21's, 20's are nice but they only really work well if you do MX. On my 450 I run 18's on an 8 in rim, but that's only for MX (less flexing on the sidewall), when I hit the trails I put on the 20's (more ground clearance). If I don't the skid plate will take some serious abuse. If I'm not mistaking I think from the factory warriors come with 22's. You need to remember when you change tire size you change the gearing. A higher tire will give more top end, but you lose some bottom. Smaller tire, just the opposite, more bottom, less top. Hope this helps, I know I'm not a "tireologist" but this is just some of the things I've found...