Bikes are amongst the most numerous vehicles of the 41st millennium and are used by a multitude of races for a variety of purposes. The Space Marines use bikes for lightning assaults and reconnaissance missions and the Eldar use jetbikes powered by anti-gravitic motors for the same purpose.
All of these armies are renowned for their ferocious assaults and fast moving battlelines. Their bikes allow them to outmanoeuvre and overwhelm their foes at key positions. The Dark Angels Chapter of Space Marines has an entire company known as the Ravenwing, all mounted on bikes and similar light vehicles who are justly famous for their skill at handling their mounts.
Bikes are treated as troops rather than vehicles – albeit they are much faster than your average trooper. They share some rules in common with vehicles, but are best thought of as fast, mobile, extra-hard hitting troops. In almost all circumstances the bike rider's characteristics are used.
Bikes fight in squads just like other troops with a 2" coherence distance. They check morale in the same circumstances as ordinary troops – enemy fire, losing an assault and tank shock.