"Motorcycles were used for scouting and lightning raids into enemy territory. They were much faster than vehicles and could easily outrun them if needed. Some of the first motorcycles had sidecars that would allow an extra passenger to be transported. While useful in urban settings, motorcycles were less mobile off-road, unable to cross trenches and other defenses that tanks could easily navigate."
Motorcycle Raiders make good alliance troops. When the enemy spawns troops and the heavy horse raiders will rush to the scene to deal with them. They have a lot of hitpoints and thus; it will fall when there are too many enemies to deal with.