Bob I just got back from riding dirt bikes in the Silverton – Lake City area of Colorado and I rode the divide road last month from Silver City NM. to I40 on my fully loaded 07 GS. The road in New Mexico was fine a little rough in the Gilla for me on a fully loaded GS but I made it on 80/20 type tires running about 25 psi. The trails in the Silverton Colorado area are as rough as I have seen them I did not care to try them on a loaded GS; they were hard enough on a real dirt bike. Knobbies are best off road but I would suggest going with the 80/20s and if the divide trail gets to rough turn around and by pass that part. The problem most likely won’t be your tires, but the 500+lb bike with 100lbs of gear your riding. Best of luck.