On Wed, 29 Jun 2005 16:48:27 -0600, [email hidden]
Quoted message said:On Wed, 29 Jun 2005 22:41:35 +0200, "Sandy"
<[email hidden]> wrote:
[snip]
Quoted message said:Take a look at some finishing sprint photos and do your own estimates.
[snip]
Dear Sandy,
A 52-degree arc would roughly double Joe Riel's 26-degree
results.
With a 52-degree arc, a 31-inch top-tube moves 13.6 inches
to either side and down 3.1 inches.
With a 26-degree arc, the same 31-inch top-tube moves only
7.0 inches to either side and down only 0.8 inches.
Doubling Joe's range of motion without sawing through the
top-tube or tearing his ankle, knee, and hip ligaments
sounds interesting, particularly when he has to keep his
balance (he has to lean his own weight in the opposite
direction) and put out tremendous effort (otherwise there's
no point to the wild thrashing).
If anyone knows of pictures that show a rider heading
forward (rather than cornering) and tilting his bike 26
degrees to either side, please share the links with us.
Onscreen rulers make it fairly easy to check that sort of
thing, and it would be nice to know what's actually
involved.
(Please, no bowlegged cowboys.)
Carl Fogel
A little measuring and calculating on my fairly normal
touring bike with 175mm pedals seems to suggest that Joe's
13 degrees to either side and 26-degree arc is close to the
limit for an ordinary top-tube
Consider the line from the inside of the high foot along the
leg toward the top tube:
leg
/
/O /
/ | 14" /
/ | / 14.5 degrees off vertical
hf_ | hf O
| | 3.5"
|_|_
|
|lf
On my bike, the right triangle from the center of the frame
tube plane, the inside of the high pedal, and the top tube
measured 3.5" plane-center to inside-of-high-pedal, and 14
inches from inside-of-high-pedal to top-tube.
That gives an angle of about 14.5 degrees, so the naive
maximum leg tilt would seem to involve an arc of about 29~30
degrees.
The straight rise from the heel on the pedal to the ankle
joint would tend to increase the effective arc, but the need
for the rider to be leaning the other way past the vertical
to keep his balance would reduce the arc.
Increasing that to the test arc of 52 degrees would require
awfully long pedals, a very low top-tube, or considerable
swinging of the hips to let the ankles and knees double the
angle.
The feet don't have a lot of swivel with clipless pedals,
and the rider is busy trying to pedal forward, so I doubt
that he's busy swinging his butt wildly from side to side to
let the top-tube fall over further.
But a picture showing an angle consistent with a 52-degree
arc would change my mind.
Carl Fogel
