I've been doing some reading on the pre-war bikes and getting some sense of models and designs, etc. The book is from BMW Mobile Tradition, Motorcycles from Munich 1923-1969.
It struck me that, up until the war, there were side valve and overhead valve models offered during the same production years. Right off the bat, the R32 was side valve and the R37 was OHV. The R11/R12s were side valve and the R16/R17s were OHV. What was the thinking on having two "competing" versions of valve trains? Seems like that contributed to dual paths for design and manufacturing. What are the pros/cons of side valves versus OHVs?
After WWII, the side valve was dropped (not sure why). OHVs seem to be the way to go in modern motorcycles. I'm just curious as to why side valves were continued for so many years.