Originally Posted by
CAJohn
Yes, the fivefinger sole is completely flexible.
I've always wondered about this 'main advantage of proper bike shoes', though. The same theory applies to running shoes, thus the arch support and generally rigid form. There's some evidence it's not accurate and that the arch of the foot transfers force wonderfully. That, in fact, is part of the reasoning behind FiveFingers. I'm not trying to be controversial, and I don't use FiveFingers on the bike currently, but I've always been suspicious that the rigid sole isn't magically better. I know clipless offers other advantages too of course, just musing about this bike-shop piece of wisdom. (edit) I've used fivefingers for about 400 miles, thus my thoughts. On the other hand, I don't do long distances at the moment, or bike races, which may completely disqualify my observations!
You can be skeptical, but the fact remains true that rigid soles provide better power transfer. When running, your heel springs up and down in relation to the ball of your foot. When pedaling, the heel doesn't spring up and down but remains in constant relation to the ball of the foot. As firm as you could hold your foot, it will still have more flex than a rigid shoe sole, and thus more power loss.