[ZwHRoTTn]

Great observation, Steve! I've seen much the same, with just one exception. With two guys and a girl riding the motorcycle, sometimes the girl may prefer sitting behind her boyfriend, hugging him, rather than sitting behind the stranger. The other variation is the girl sitting in the front of the driver (his b/f), ducking down so he can see. Haven't seen this last one myself, but just heard of it from my friends.