If its on the Grand Prix Circuit, well
Copse Inside in the stand, they fall off alot their ;-)
Club Outside: you will need a lens bigger that 500mm
Abbey Outside in the blue stand, with the small seats is good, will need more than 300mm their
Priory Corner, they fall off alot their aswell,
Luffield Corner, is pretty good also..
Thats basicly it for bikes, its not a bike freindly photography circuit :-(