In my and the neighboring club, A is slow, & C/D is fast. Some visitors have been sandbagged or bored.

Weekend rides post distance, pace, & climbing info. & some idea of drop/regroup protocol. There is a leader, but you are expected to be self-sufficient on anything but a beginner ride. Rides sometimes split into faster/slower groups, and individuals often join or leave the ride at different points. An LBS hosts the weekday evening hammer-fest, with once a month being 'take no prisoners' style, and the others a bit more social.