in message <[email hidden]>, ok
(') said:Simon Brooke <[email hidden]> wrote in message
news:<[email hidden]>...
Quoted message said:in message <[email hidden]>, ok
(') said:Can anyone help me before I pour out a fortune?
I bought this bike 2nd hand about a year ago. I have never really
tried to sprint on it and always found it difficult to keep up with
others going beyond a leisurely pace. I know I'm not that slow as
I am fairly fit and have done a fair bit of long distance cycling
on
touring bikes on holidays. It's driving me nuts now and I don't
want
to pour money down the drain on it. Help!
That bike is never going to be fast, it isn't designed to be. As
others have said the riding position is too upright, so you've got
too much aerodynamic drag. That said there are a number of things you
can do. The first is to fit slick tyres (ones with no or virtually no
tread pattern) and to pump them up very hard (100psi or higher). The
second is to lower the handlebars as far as they'll go. Keep the seat
up to a height where you're almost but not quite straightening your
knee on each pedal stroke (see Jeremy Collins' post).
But if you want to go faster the only real solution is to sell that
bike and get another, one which has its saddle at least as high as
its handlebars. Drop bars help, too, because they give you a choice
between a moderately low riding position with your hands on the tops,
or, when you're going faster or there's a strong headwind, a still
lower riding position with your hands on the bends or drops.
Thanks for the advice. It makes sense. However I'm a little confused
in general though about this type of bike. I cycled on a touring
upright bike in France approx 50 miles a day at a fast pace. Never
had any trouble reaching high speeds on it. I also cycled for a week
in Ireland, also on roads and on a touring bike and again had no
problems going fast. My bike does not look dissimilar to those two.
Why can I only go at a leisurely pace on this? How would I have known
in advance?
The critical issue is the angle of your torso to the horizontal. On your
bike, the saddle is significantly lower than and quite close to the
handlebars. Consequently, you must sit more or less upright or else
your arms will be uncomfortably flexed. Also, the bars are fairly wide,
causing you to hold your arms open. Compare with a time-trial bike e.g.
<URL:http://www.london2012.org/en/news/archive/2005/january/2004-01-06-18-00.htm>
- the handlebars are much lower than the saddle and the rider's torso
is almost horizontal, while the hands and forearms are very close
together.
Cycling aerodynamics are not straightforward because the human body is
not a very aerodynamic shape. However, aerodynamic drag at best
increases in proportion to the square of the speed[1]. To get some
feeling of what this means, if you cycle on a racing bike on a flat
road on a windless day
at ten miles per hour your power input is about twelve watts
at twenty miles per hour it's about ninety watts
at thirty miles per hour it's about three hundred watts
Clearly, these are big differences, and the more you can do to minimise
them the better.
At a crude level aerodynamic drag relates to 'frontal area'. That is to
say, if you took a lifesize photograph of yourself cycling with the
camera straight in front of the bike, and then you cut around yourself,
the area of the piece of paper you'd get. This isn't perfect because it
doesn't account for turbulence but it's a good first approximation.
Clearly, if you're sitting upright you'll look quite a bit bigger in
the photograph than if you're really crouched down - your frontal area
can be at least half again bigger sitting upright than crouched.
At ten miles an hour that isn't much difference, because sitting up
merely increases that twelve watts to eighteen watts, and at eighteen
watts your body is barely ticking over. But at thirty miles per hour
its an increase from three hundred to four hundred and fifty watts, and
that's taking you into serious athlete territory.
Obviously there's a trade-off with comfort[2]. But on a well set up bike
a racing crouch does not have to be uncomfortable (although it
certainly takes getting used to). But in simple terms, a fast bike has
its handlebars lower than its seat.
[1] in practice it may be much worse than this, because of turbulence
and vortex shedding.
[2] unless you choose a recumbent, where better aerodynamics can mean
greater comfort.
--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; Men never do evil so completely and cheerfully as when they
;; do it from  religious conviction."          -- Pascal
