Jerry...The over rev problem at the end of the straight with the 13 tooth sprocket was due to the added torque and go it pulled mega quicker and ran out of gear....sure I could have shifted but on a blue groove track I find shifting actually slows me down....If I gear it correctly I usually scream into the turn and pitch the quad to scrub off just enough speed to power thru and out of the turn.... I guess I'm an old school racer....LOL