If you are panning the shot (following the subject) Depth of Field is completely irrelevant.
Put your camera in Tv mode... start with a reasonably higher shutter... for bikes, start at maybe 1/500 - now follow the bike ... shoot.... keep following.
You should also set the camera to a single focus point (sensor).
Once you're getting good results, start lowering the shutter speed. 1/400 - 1/320 etc.
With bikes, you'll not need to go too slow. Ultimately, you will reach a point where something is NOT sharp... you may have a sharp section in the image.. but other areas will be soft. This is normal as you slow the shutter down. With cars... that can be acceptable. With bikes, you'll want the rider and the bike to be sharp. So, unless you're going for "art"... don't get it too slow.
The zoom range is not necessarily a factor... but it does make a difference in your movement. Remember, an object further away from you is passing you at a slower rate. Closer to you, it is passing at a greater rate. Speed blur and panning is all about the camera movement. You'll want to position yourself at a distance from the subject that allows you to pan smoothly and comfortably. Too fast is jerky... to slow is wobbly. So a zoom can help you fine tune the distance to fit YOUR panning motion to the car's rate of travel.
If you search this part of the site, I'm sure there are some tutorials of mine that talk about panning.