Wull and I basically just said the same thing, but coming at it from different directions. Sorry if that's confusing. Wull's method is better for understanding panning (as shutter speed directly controls the amount of blur caused by the panning motion), my method of using aperture will really only help you on the non-panning shots. Using AV mode to shoot nearly or at wide open on your lens, and filling the frame with the bike (not always easy!) will create depth of field that separates the bike from the background. I've included some photos to hopefully make that clearer.

This shows why you'd use AV mode - picking an aperture close to wide open in order to separate the car from the background. This shot is almost wide open aperture on my 70-200, at F/4.5, ISO 100, and a shutter of around 1/1000.


And here's an example of a panning shot. Shot at around 110mm on the 70-200, F/9, ISO100, shutter of 1/80. Again, shot in AV mode where I chose F/9 knowing the camera would chose a pretty long shutter that would give me the blur. However, the downside of not choosing the shutter speed myself is that I got 1/80, and I would never recommend choosing a shutter speed that slow if you want consistent results. I got a bit lucky that I got the car sharp in this one.



I hope that helps. Good luck, have fun, and show us some of your shots (good and bad) b/c that's how we all improve around here!