OK gearheads can anyone give us the reasons for the various different angles of twin cylinder architecture? BMW 180, Honda 51(?) Harley 45(?) degrees etc, etc. I know that the BMW mill has opposed cylinders, and that should lower the CG. It should also negate the need for a lot of counter balance weight on the crank. It should allow the tranny to hook directly to the crankshaft shaft as well. (I think?) Anyway, what's the thought behind the other cylinder angle configurations?

 

90 degs. (RC51, Ducati, Suz TL/SV) - perfect primary balance

60 degs. (Aprilia) - narrower angle allows engine to be rotated forward for better weight dist. Vibes muted via counterbalancers.

BMW - funky. 180 deg. horizontally opposed cylinders do optimize air flow for an air cooled engine, though.

Harley (50 degs. IIRC) - doubles as a paint shaker, and the vibes will improve your chances w/ the women.