Hi Brendon,
Motorsports can be quite challenging for novice photographers.
Half the challenge lies in the unpredictability of the different riders; ideally you want to get close to the subject but you are also aware of the intrinsic dangers involved. If you come back too far, then you tend to weaken the image.
There are many different ways we can approach the subject but I'm going propose two to you.
The first is simply to step back a little bit and use a longer lens. With a longer lens you can crop into the subject, if you want to imply some movement you can use a slower shutter speed (something about 1/60s at 100 ISO in these lighting conditions would be a good starting point).
The second option I would propose would be to get yourself a remote cable release that plugs into the side of the camera and lets you trigger the shutter up to about two metres away. Place the camera on the ground near the track (preferably just out of range of where the motorcycles are likely to be) and try triggering the shutter just as motorcyclists go past. The low perspective should add some drama to the image.
Hope this is a help,
Anthony.