buckyllama wrote:
...
Having said that I'm trying to pin down what the bent community means
when they say a bike is "fast" or "slow". I mean it's obviously
related to seat angle and BB height. a Tour easy is a differnt beast
than a bacchetta aero. But how about the different between something
like the aforementioned aero and a street machine. BROL describes the
aero as fast and the street machine as being kind of slow. But the
riding positions are similar. (particurlarly on the 26/20 version of
the aero) A quick analysis of the side pics of both bikes suggests
that with a similar seat angle the frontal area would be quite similar.
Is weight the major player in this comparision then? Or is it a more
amorphus "this bike feels fast" kind of judgement....

While frontal area is an important factor as it largely determines
aerodynamic drag, there are other issues in seating position. Combining
a reclined seat with a relatively low bottom bracket (BB) will reduce
the amount of power the rider can generate for acceleration and
climbing. A seat with variable recline [1] could be used, but would add
weight and mechanical complexity.

Another issue is rider comfort. A rider will generally be faster
overall if he/she is comfortable on the bicycle, even if there is an
objective performance tradeoff to gain that comfort. Leave riding fast
in pain to the UCI professionals.

To state the obvious, rolling resistance and drivetrain friction will
also affect performance, but to a lesser extent than aerodynamics
except for low speed climbing.

[1] Here is one of the very few bicycles with variable seat recline
http://www.fortebikes.com/images/gallery/SEAN2.JPG.
--
Tom Sherman - Fox River Valley
"Abnormal would be a mountain lion speaking English." - M.V.