[NuclearFishin]

Respectfully, I think you're both right. Certainly recumbent bikes are aerodynamically efficient, but it's worth considering that in a bike race one also needs to ride uphill, and the instability of a recumbent at slow speeds would be a disadvantage here. I haven't checked, but I suspect most hill climb records would be held by traditional bike frames.

[SeanLuke]

I don't think recumbents (at least high-racers) are necessarily unstable at slow speeds. My understanding was that the fundamental problem with recumbents in racing is that, going uphill, aerodynamics matters less. What really matters is applying torque efficiently. And humans are designed to apply torque vertically: we're good at it. So while on the straightaways and downhill recumbents cannot be beaten, they are poor at climbing.

What's frustrating is that we'll never get to see serious comparisons of the two, or of interesting combinations of them, in real races because UCI banned recumbents for the worst of reasons a hundred years ago.