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Center of Gravity

Joined
Mar 2, 2001
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#1
I am reading Semics' book Pro Motocross Riding Techniques and find it to be full of very useful information. One point I'd like to comment on, however is the effect of riding position on center of gravity. He states that standing on the pegs lowers the center of gravity because the weight of the rider is held lower on the bike (the pegs) than when sitting on the seat.

Thinking about this for a while now, I'm not sure if I agree with this statement. Standing, as opposed to sitting, may alter the COG of the bike, but we are not just talking about the bike, we are talking about the bike/rider combo. I think that standing must raise the COG of the bike/rider since you are higher off the ground when standing.

I do agree, however, that standing on the pegs puts PRESSURE lower on the bike, and can affect handling tremendously.

By the way, Semics goes on to contradict himself in the cornering chapter by saying that you want to sit in most turns because sitting lowers the center of gravity.
 

HiG4s

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Mar 7, 2001
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#2
Originally posted by AngryCandy:

Thinking about this for a while now, I'm not sure if I agree with this statement. Standing, as opposed to sitting, may alter the COG of the bike, but we are not just talking about the bike, we are talking about the bike/rider combo. I think that standing must raise the COG of the bike/rider since you are higher off the ground when standing.

I do agree, however, that standing on the pegs puts PRESSURE lower on the bike, and can affect handling tremendously.

I can agree with most of your accessment, except I would think when standing only the bike needs to move around to compensate for bumps, cambers and such, so the CG of the part that matters has gone down, and for the most part the CG of the bike and the CG of the rider work independently. When sitting where one goes the other has to follow.
 
Joined
Feb 2, 2001
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#3
The center of gravity has to do with relation to the bias of the weight and with the suspension. The COG is a property of the suspension system. All the weight of the bike and rider have to go through the suspension in order to contact the ground. Standing on the pegs lowers the COG because it is putting the weight of the rider in the lowest part of the bike in relation to the suspension, the pegs. This is the case when you are riding straight up and down.

When you are cornering the ideals for COG change. During cornering the angle of lean mainly helps determine the turn radius. The COG emphasis now changes to a lateral, or side dimension. Getting lower on the bike makes higher lean angles possible to help cornering. Just think of two different size sticks. Stand them on one end and release. The taller stick falls slower than the shorter one. Same idea is in cornering.

Hope that clears things up. :)

[This message has been edited by krash133 (edited 03-20-2001).]
 
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