You can run solid axle rims on an IRS but you cannot run IRS rims on a solid axle. The offset of the IRS rim is to the positve side pushing the tire in towards the chassis. So as long as the offset is to the negative you can run wider rims. I have put a set of aftermarket tires and rims from a forman on my Rancher AT all it did was push the tire out farther from under the wheel wells., but I now run stock width on 27" tire with aftermaret rims but to be honest I don't know my offset with out going out and measureing. I just told the guy what bike I had and that was the offset he ordered for me and the tire sit under the fenders like they are suppost to.