Downhill bike races can be very tough to shoot the first time.
Hike down the course.
One to two flashes will suffice.
Know where the gnarliest parts and best corners are.
Trails are uneven.
Get a tripod at wal-mart or target for $20.
It will be lighter and have adjustable legs for the uneven trail.Bring ball bungee cords.
(i.e.
climb a tree, lay on the ground, whatevery makes your shots different!
)Shoot in locations where other photographers are not.