You will probably be better off with a smaller lens, such as a standard 50 mm or 28 - 80 mm, as you might battle to keep a 300 mm lens still and focused on the back of a motorcycle. Sports photography is usually shot with a fast shutter speed to capture the moment. If you have an auto camera, then select a fast shutter speed (1000) and let the camera decide the f-stop for you. If you are a purist with a manual camera, then you'll have to rely on a light meter to get the f-stop right. Another important factor is film speed. 100 or 200 ASA film is perfect for sunny or bright, cloudy days. Maybe slap in a 400 ASA film right at the end for some "atmospheric" shots. 400 ASA film is grainy, great for the artistic animal in you.
And here's a tip: Use the camera flash. Try and over-ride the automatic flash setting on the camera, so that the flash is always on. Use the shutter speeds and f-stops as described above, but let the flash fire aswell. If it's a bright sunny day, the natural light will "tone" down the harshness of the flash, while the flash will help to eliminate shadows and give you a much brighter shot. If you are afraid that the flash will over-power the natural light, then close the aperture one stop.
To prepare yourself for the big day, visit some cycling websites that have photographs you can browse thro. That will give you some good ideas for composition.
Good luck and remember we want to see those pics!
