Replying to Tips for filming DH biking

Looking to shoot some DH mountain biking this summer and was just wondering if anyone could enlighten me with any tips or strategies you've picked up while filming. I was looking to shoot a few things with a glide cam and mostly a long lens on a tripod. I was mostly wondering what the most efficient way to film is? Do you start at the top of the run and get the biker to stop and start in sections? Or should they just lap and I pick my spots as they come down?

Any advice on the process would be great. Thanks.