Originally Posted by
mazdaspeed
I don't think there's any loss in actual efficiency just because of the frame flexing. You're turning the cranks which are directly linked to the rear wheel, if the frame flexes that's just something it does, I don't think it's significant. The weight and handling (handling being a function of the fork and geometry mainly) are the major differences IMO.
I would respectfully disagree with you about frame flex. If I could get my younger legs back and took going fast seriously, I would want the stiffest bike I could stand. The energy lost through a flexing frame may not be very noticeable, but it is still real. I like steel frames because comfort is more important to me these days. But, I still ride my aluminum frame with carbon fork more than any other bike. I've never ridden a carbon frame, so I can't comment on them.