Originally posted by KxBlaze The smaller the aperture (F22 or maybe even more) the greater the DOF so try that first and also the longer you zoom in the less DOF you will get so if possible try to shoot that shot at <500mm.
The various suggestions about DOF are good. You're kind of stuck because if you close down too much, you may not have a fast enough shutter speed to freeze the driver in front. On the other hand, a bit of motion blur might not be a bad thing.
Before making a commitment to reshoot you might try some test shots. Go back to the site, with or without bikes on the track, or work at another site such as a curve on a highwiay with similar distances. Run through the apertures at different focusing distances to see what you actually get for DOF. (One thing you ought to consider is prefocusing rather than using AF.) Then you'll know whether it's doable and can commit, or decline, or offer alternatives with confidence.
I was often asked to do fairly tricky technical things when I was a full-time pro. If I had any doubts, and if there was time, I preferred to test and then state clearly what I could deliver. That is a lot better for credibility than blowing a commitment.
John