The highlights are majorly blown out in the first couple of shots.
Are you shooting RAW (or setting your camera to minimum possible contrast if not)?
If so, I'm not sure what else you could do, really to get the higher dynamic range you need. Flash would be ineffective (if even allowed or close enough), because the problem is high contrast suits and bikes, not subject vs. background. Neutral density gradients won't help for the same reason (local not global contrast). Can't do HDR because they're fast moving subjects.
My only remaining suggestion (if you're already using RAW and still getting too much contrast) would be going back and shooting again on a more overcast day if possible, since this seems to be a facility that has races at it on a regular basis.
You might want to use a bit slower shutter speed so the tires and spokes are motion blurred a bit more. It helps convey a sense of speed.
Great action shots. But it looks like you lost details on the white and it is overexposed. What setting did you shoot at?