Originally Posted by ratdog
You can't say that it's the only way to make a folding bike & that's where the argument falls apart. It's a bold face attempt at copying a sucessful design without even an attempt at changing the curved top tube. I doubt that Merc even went through the trouble at looking at possible different geometries in order to avoid any possible legal claims by Brompton.
Not to descend too far into the hell this thread has become but from an engineering perspective if can quite successfully be argued that the curved top tube is an arc; one of the strongest structures in engineering. Why do you think we have arches? In a bike frame it will better resist torsional loads on it since it is one piece.
It could also be argued that the curve in the top tube is there for functional reason to more closely follow the curve of the rear tire when folded. This is where the expired patents could be used against Brompton.