"Sunset Lowracer [TM] Fanatic" wrote in message
oups.com...

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.

The only thing I would add to Tom's excellent message on recumbent bike
design is to be aware of high bottom brackets. Very many of us will get numb
feet if the BB gets much above the seat. A high BB will also affect handling
to some extent. Hence, the reason why so many recumbents have a low BB. It
is the classic design and for good reason.

I have always thought that the Tour Easy could have a slightly higher BB in
order to ensure more rider comfort. But the BB cannot be higher than the
seat or I will get numb feet. I think this may be more of a factor as you
age, but I am not sure about that. I have also known a few young riders who
cannot take a high BB.

--
Ed Dolan the Great - Minnesota
aka
Saint Edward the Great - Order of the Perpetual Sorrows - Minnesota