"Motorcycles were a common sight on WW II battlefields, but mostly fell out of military use afterward. The last U.S.Army commission for Harley-Davidson was the 1957 Sportster XLA. This was intended as a patrol bike, not a combat vehicle and only 418 were ever manufactured. The surplus of military motorcycles enabled the rise of outlaw biker gangs in the US, supposedly comprised of veterans who missed the excitement of life in war time. At the same time, motor scooters like the Vespa became popular in Europe as a safe and practical means of civilian transportation (with no 'outlaw' connotation whatsoever)."
Veteran 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.