Foolproof le mans pics?

[cavebloke]

Off to le mans in a few weeks with the SLR and I was hoping you guys could give me a few tips on shutter speeds. Are there speeds that you use for motorsport that always give a perfectly blurred background but nice crisp car? Obviously it depends on the speed of corner and your panning ability. Can anyone suggest good ranges to work in? I don't want to pay for developing of a load of films of rubbish!