Measurement of sitting position on a recumbent.

I am trying to write a bit of software that will calculate the position of
the Centre of Gravity (or Mass if you like) for the human body in the
various positions that might be found in cycling. For an upright I can
work it out from the relative positions of BB, saddle and handlebars, but
for a 'bent there isn't an easily identifiable equivalent to the saddle
position, and the position of the hands does not tell me the position of
the trunk in the same way that an upright does.

If I were to ask recumbent riders for their hip position, both vertically
& longitudinally, do you think you could find yours when sitting on the
'bent?



Mike

On Wed, 08 Feb, Mike Causer wrote:
I am trying to write a bit of software that will calculate the position of
the Centre of Gravity (or Mass if you like) for the human body in the
various positions that might be found in cycling. For an upright I can
work it out from the relative positions of BB, saddle and handlebars,

Only if you make assumptions about relative lengths of arm, leg and
trunk, which differs significantly between average male and average
female, even before you get to individual variation. How do you
address that?

If I were to ask recumbent riders for their hip position, both vertically
& longitudinally, do you think you could find yours when sitting on the
'bent?

Relative to what? BB?

Still doesn't tell you where the CoG is - my recumbent will let me set
the seat at a range of angles, and at any point oin the range my hips
are at the same position relative to the BB, but the height of CoG of
my torso above teh road surface probably varies by 50%.

regards, Ian SMith
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On Wed, 08 Feb 2006 21:22:14 +0000, Ian Smith wrote:

Only if you make assumptions about relative lengths of arm, leg and trunk,
which differs significantly between average male and average female, even
before you get to individual variation. How do you address that?

Anthropomorphic data off the net for limb length and mass against height
and sex. Mostly measured from Russian corpses in the 1930s apparently.
They had a lot, and they're still the most comprehensive data-set.


If I were to ask recumbent riders for their hip position, both
vertically & longitudinally, do you think you could find yours when
sitting on the 'bent?

Relative to what? BB?

The ground and front axle line.



Still doesn't tell you where the CoG is - my recumbent will let me set the
seat at a range of angles, and at any point oin the range my hips are at
the same position relative to the BB, but the height of CoG of my torso
above teh road surface probably varies by 50%.

I need seat angle too. And for ASS whether it's arms straight or
praying-mantis style -- although the arms are light enough that it won't
make much difference. So I might ask but ignore the answer ;-)


I /am/ assuming that anyone interested enough in the final results, which
are about braking performance, will take a little bit of trouble to find
out their own numbers. After writing some bits of program which try a lot
of cases of grip against upright and recumbent configurations for my own
bikes I found that there are is a lot of misinformation around, and would
like to produce a website with which people can play with the numbers,
along the lines that http://www.kreuzotter.de/english/espeed.htm does for
speed. In theory the two most important things about braking are the
grip (tyre/road friction coefficient) and the position of the riders CoG
relative to the front & rear tyre contact with the road. In real life
experience and ability to judge conditions and modulate the brakes
probably balance the theoretical factors, but are not measurable.



Mike

On Wed, 08 Feb, Mike Causer wrote:
On Wed, 08 Feb 2006 21:22:14 +0000, Ian Smith wrote:

If I were to ask recumbent riders for their hip position, both
vertically & longitudinally, do you think you could find yours when
sitting on the 'bent?

Relative to what? BB?

The ground and front axle line.

I think I'd find it by photographing myself from the side and
measuring off the picture. Shouldn't be too tricky, but I've not
tried it, so there may be a difficulty I don't foresee.

regards, Ian SMith
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