On Tue, 18 Jul 2006 07:15:29 GMT, Michael Press <
[email protected]> wrote:
>In article <Zc_ug.203411$iF6.99687@pd7tw2no>,
> Michael Halliwell <[email protected]> wrote:
>
>> Snippy Bobkins wrote:
>>
>> >"Chris Z The Wheelman" <[email protected]> wrote in message
>> >news:[email protected]...
>> >
>> >
>> >>I have a hardtail, with a ThudBuster and sprung saddle, mainly for
>> >>comfort. In the really rough stuff I found it best just to stand up (and
>> >>lower my C.O.G. in the proces).
>> >
>> >How does one stand up, and lower one's C.O.G. in the process?
>> >
>> When standing, you are applying the load of the riders weight via the BB
>> vs the seat...although the riders centre of mass moves up slightly,
>> where it is applied to the bike is greatly lowered.
>
>Center of mass and center of gravity are two names for the
>same point. Will you describe what you accomplish by
>moving the load from saddle to pedals? Thanks.
Dear Michael,
Pegs and pedals are the same for bicyclists and motorcyclists, so
pardon the following.
Standing on the pegs does raise the center of gravity.
However, standing moves the effective point of control down to the
pegs, which are also broader than the seat.
And standing means that we balance on a pair of feet, which is
considerably easier than balancing on a pair of of buttocks.
Standing frees the hips to move much more for balance, which rough
stuff requires.
Most of all, standing increases the polar moment of inertia. A rider's
hips are roughly his center of gravity, so raising them makes
balancing much easier by simply moving them farther from the pegs.
The usual example is that it's hard to balance a short pencil upright
on the palm of your hand, but most of us can balance a yardstick that
way. The increased distance between the palm (pegs) and the center of
gravity of the stick (hips) is what makes it possible.
This is why trackstands are easier when standing instead of sitting,
and why trials riders stand to negotiate circus-style obstacles.
Modern trials motorcycles have effectively removed the seat, partly to
save weight, partly to allow more knee movement to the side, and
partly because seats served no purpose in competition:
Here's an old trials machine:
http://www.oldrice.com/TL250_Brochure_2.jpg
Here's a modern trials machine:
http://www.geocities.com/fn_owens/gasgas/0528.jpg
Compare the top contours, and you'll see that there's just empty space
where the seat used to be.
Trials bicycles got rid of seats much sooner. Here's a trials bicycle:
http://www.tryalsshop.com/ScorpaUSA/Bicycle/Bicycle-Photos-06/Bike-Top_lg.jpg
So much for the fuss about long seat tubes on compact frames!
In addition to balance control, standing also lets the rider use his
legs and arms as shock absorbers over rough stuff.
For bicycles, a further advantage is that the standing rider has
maxium leverage and power--we stand partly to make it easy to put our
weight on the pedal, but also because it straightens our bodies at the
hip--the closer we are to an normal upright posture, the harder we can
shove down.
For motorcycles, standing makes footing much more effective. You have
greater reach forward and sideways with either foot because of the
increased freedom. Sitting to paddle requires more and feebler dabs.
If you want to get over that ugly ledge-and-turn with only a single
penalty mark, you want to plant one foot well forward while standing
and lever around it.
Cheers,
Carl Fogel
