Size of group

A.
Keep the groups small and manageable with riders of similar competence and experience. This is the most important rule.

F.
Large groups are dangerous. Individuals in a large group behave dangerously,
trying to get to the front of the group, trying to stay with their mate, not
being aware of the closeness of other riders, not being aware of the ability
of other riders. Visibility in a large group is restricted, individual
riders get little advance warning of hazards, and often simply go with the
group instead of observing and reacting in response to a hazard. If a group
is likely to exceed say 10 riders, break it into two groups, each with its
own leader and sweeper.