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Cornering, center of gravity, and torque(4 posts)

Cornering, center of gravity, and torqueContinental
Feb 4, 2003 7:18 AM
Yesterday there was a post about cornering techniques. It stated that putting your weight on the outside pedal lowers the center of gravity. I replied that shifting weight does not lower the center of gravity. However, shifting weight is beneficial. Shifting weight from the seat to the pedals changes the torque on the frame. Torque, or twisting force, is force times the length of the lever. During cornering there is a force perpendicular to the frame due to angular acceleration. When the weight (force) is on the seat then the seat tube and seat post acts as a long lever arm which creates a large torque on the frame. Shifting the weight to the outside pedal shortens the lever and reduces torque, or twist, on the frame. I think I have the physics right, but wouldn't stake my life on it. In any case, it's all academic. Great athletes figure this all out with their bodies and have the fluid intelligence and coordination to corner with speed and grace. The rest of us either slow down or get road rash.
and maybe more importantly?DougSloan
Feb 4, 2003 7:29 AM
In a corner, it's vitally important to keep the tires pressed against the pavement. If you hit a bump, that tends to load and then unload the tires, and when unloaded, yikes, no traction.

Putting weight (or pressure) on the pedals vs. sitting on the saddle tends to turn the legs into shock absorbers/springs, allowing the weight of the body to become sprung, thus keeping the tires in contact with the road better.

Isn't this part of the "weight the pedals" reasoning?

You're right--the simple, obvious reason is key. nmContinental
Feb 4, 2003 9:32 AM
Not so simple53T
Feb 4, 2003 10:40 AM
We are talking about a system consisting of two loosly coupled, fully articulated bodies traveling at 25 mph. Furthermore, one of the bodies is alive, and subject to unpredictable motion.

This is not a simple problem. Weighting the outer pedal does make the whole human mass sprung through a damped system. Remeber that when sitting the mass is sprung, but the system is less damped than when you use you leg as the spring. It also is a great way to maximize cornering clearance. Contrary to what some have said, riding lower on the bike does lower the CG, and a classic cornering posture is low on the bike. (If you hung off the bottom of the frame, wouldn't your CG be lower?) It could be reasoned that lowering the outside pedal allows you to stand without raising the CG.