Bike riders can choose to shoot either personal arms or bike-mounted weapons using their BS. If the entire unit remains stationary they can use rapid fire weapons carried by the riders at full effect.
As weapons are firmly mounted with plentiful ammunition supplies, any weapons mounted on a bike can fire as if they were stationary even when the bike has moved. Hence any rapid fire weapons mounted on a bike always get two shots at targets up to 12" away or one shot at targets up to 24" away. Even heavy weapons can be fired by moving bikes.