you might wanna try only getting single riders. as well as getting rid of background clutter. but as far as single riders go, when theres multiple it looks good if its on first corners..or straightaways. just my little input. thats a personal preference though. other than that, the colours look great, as well as shutter speed.
I am still learning my camera, was taken with the preset for daylight/cloudy. The riders of the club are telling me they like the way I am "in their face" when I am on the track. The dirt and mud down my shirt and on my camera is just as great as on the riders at times. (my way of being part of the race) They know where I am and put extra effort on that part of the track.. Others (photographers) take their pics from across the track with longer lens' and seem to get only the ordinary shots.