Well you are on the right track by taking OCF. However I have a couple of comments
#1 could have done with a faster shutter speed. The 3\4 panning is hard to get right. I would have tried to freeze the rider here, rather than panning to show speed that wasnt there.
#2 Less flash and less ambient would have worked well. The concept is right, But I probably would have used a smaller aperture to dial down the flash a bit
#3 is nice - only crit is the little bush in front of the rider is distracting. Also lift the flash a bit higher, to try and keep the light off the ground.
#4 I would scrap - sorry
#5 Flash in the scene is a bit of a no no, unless that is what you were going for. Nice balance of flash to ambient though. Once again bushes are distracting.
#6 same as #4 sorry.
#7 faster shutter maybe? I dont know really. This shot would have been nice from the front and really low.
#8 Nice - only crit would be another flash camera left to light under the peak of the helmet.
Sorry if I sound a bit harsh. This is just my opinion