My buddy wants me to bring him a new front tire for his XR400. We went up the Rockman sand wash to the switchback on our last trip. Now my pal wants a fat one on the front. On our next trip we're going to Santa Maria's ruins and ride the Rockman the other way from highway one. What is the biggest 21" front knobby for sand. He's willing to take a disc to the side knobs to make it clear if necessary. At one time he had a Yamaha Big Wheel BW200 and we both know that would be like a cadillac on that bitch of a sand wash.