Probably too late...sorry, but maybe for next time.
Zoom blurs are a lot of fun. I shot this one at 1/6th second. I prefer around 1 or even 2 seconds. Just zoom the lens during the exposure - in or out makes a difference. Try both. And you can zoom a bit, stop and zoom some more.
I was going for the starburst on the setting sun and a silhouette on the ride for this one. Settings at f22 for the starburst and 1/160th to stop the slow moving ride and -1 Exposure Comp to get the silhouette.
This is just a long exposure to get all that motion and a very wide angle to get more than one ride. 5 seconds at f13 and ISO 100.
