On my KLR 650 I ran stock sprockets (15/45) to Salida, CO. It is mostly good roads, flat land and low elevations up to there. In Salida I switched to 2under/2over (13/47) for the steep rocky passes, higher elevations, sand and lower speeds on the rest of the trail. With 2under/2over I did not have to worry about changing chain length. You can go back to stock sprockets for the ride home. I would not want the hassle, weight and space of carrying extra tires. Just in to Colorado at Trinidad the trail passes right in front of a good sized motorcycle shop called Valcom Motorsports that caters to riders on the trail. Also, arrowhead motorsports in Moab, UT caters to riders on the trail. You can call ahead to either and if they do not have what you want, they will get it for you. I used Kenda 270 knobbies front and rear. They are a good duel sport tire. Long life with not too much noise and vibration on the highwayand good traction for sand, gravel and rocks. I put 11,000 miles on the rear tire before I changed it. It was really really worn out at that point, but no threads were showing.