Originally Posted by SDS
Well, he might be small somewhere.....
The biggest problem with long cranks is GROUND clearance. It doesn't really matter if you aren't going fast or are only going in a straight line, but if you are doing a road race training ride, and you have to keep the draft or you are in big trouble, tagging the pedals on the ground with a 10.75" BB height and 185mm cranks is a real issue.
Crank length (bicycle's, not 55-11' Superman's) is even an issue if you aren't racing. My tour bike has caged pedals (clips and straps) with a low-ish bottom braket and 175mm cranks. I've managed to scrape a pedal on either side going only 12-15 mph, so I think I understand why the extended length crank arms are more popular on MTBs than elsewhere. Turn clearance is aggravated because 175s and higher generally have a higher Q-factor to avoid fouling the chainstay.
55-11 must be a Superman. I can't imagine mere mortals attaining 40+ mph with the built-in headwind he must have from the constant hot air he spouts.
Maybe that indicates a "super" lung capacity.