I believe I need some new tires. I am just doing general all-around riding in the hi-desert of california - dirt trails, some sand, some rocks. My '87 XR600 currently has a Dunlop D739FA 80/100-21 front and a Bridgestone ED-12 110/100-17 rear. The front seems very unstable on slight sandy jeep trails, even with my slightly flexable steering stem (bad stem bearings - soon to be fixed). I have played with the air pressure and it seems best at around 12-15psi front and 15psi rear; but it could be much better. Any recommendations? Thanks.