Found a great video while trawling through the web earlier this evening. It's a documentary about the Ken Fox Troupe, one of the last remaining families who travel all over Europe and perform the famous Wall of Death routing using motorcycles and quad bikes. I particularly enjoyed the fact that one of the bikes they use is a 1920's Indian which is preferred because of its reliability.
THE WALL OF DEATH from benedict campbell on Vimeo.
I remember seeing this kind of act in circuses when I was a kid, it seemed impossible until you understand how centripetal force works. Then a couple of years ago Rosa and I attended the Moscow Circus on the Gold Coast. Terrific show but the highlight was the Ball of Death. This act is truly one of the scariest things I've ever seen. It's one of those where you have to remember to breathe.