Originally Posted by baxtefer
2. efficiency - the momentum of the rear wheel kind of pushes your legs past the dead spot, making it seem a bit easier.
No way. If you wait for the drivetrain to push your leg around on a _hill_, you will not even make it to the top, let alone clock a fast time.
The way I see it:
1. You are forced to push a higher gear so you put more effort in
2. The fixed drivetrain is quite a bit more efficient, as the chain doesn't bend all over the place (crosschaining esp. drains a lot of energy). Figures like 5 to 10% are quoted by some, and low cadence, high power situations with the chain crossed will definitely be the most ineffective ones. 10% is an _immense_ difference.
(drivetrain test: put a gearie and a fixie on reapir stands beside each other, put the gearie in the same gear as the fixie, and spin both rear wheels backwards. Fixie drivetrain spins forever.)