In Arcade mode, any rider will do, find a Clean Section checkpoint (2 green signs each side of the track) but find one on a straight. Stop your bike about 30 meters back. Wait until you have 3-4 seconds left on the timer, now accelerate flat out and the time should expire BEFORE you get to the checkpoint, but the speed you already have should carry you across. If not try again to suit your situation. I suggest doing a lap then trying this on the Start/Finish straight as you have more room. Good Luck.