It's a sidecar for racing only. There is no seat for the passenger because he never sits. The passenger moves all over the bike as a counter-weight because the rig doesn't lean. That's why passengers are often called "monkeys".
Sorry Steve- you must have just slipped in there before me.
Have to say I don't know why you think they would mostly be 2-strokes, though. Many 4-stroke Brit bikes have been raced and in the '50s and '60s BMW had quite a few successes. If I remrember anywhere close to reality, the Honda engines where giving folks quite a run for the money somewhere around the '70s and up.
The USA recently sent a rig from the San Francisco area to the IOM. I'm afraid they were both hurt very badly, however. I seem to remember he put a Yamaha XS650 engine in it. I think perhaps the 2 cylinder engines might have been preferred to save weight and because they tend to get power down low easier.
On the other hand, I could be full of it.
I'll swear that at least some of this post is true.
