Questions on more bike physics
June 10th, 2008 ecoliThis continues the series I started the other day, answering questions about the physics of bicycles. Well, now I have some questions of my own. Questions that need answers. Answers that are worth millions of Shrute bucks.
I made some observations while on my daily bike ride today that I couldn’t explain the physics of. It was related to this statement I wrote in my previous post:
Another interesting affect about turning while on a bicycle is called “counter-steering.” If you were to travel along a straight path and simply turn the wheel to the right, you’d simply fall over. This is because the center of mass must be under the bicycle in order to remain upright. Turning the wheel moves the center of mass out from under the bike. In order to successfully turn, you must first steer the bike slightly in the opposite direction of the turn in order to shift the center of mass to the correct position so you can later lean for the turn. It’s the same principle as balancing any object on your hand. You have to move the bottom of the object to the direction that the top of the object is falling, in order to reposition the center of mass. While this slight turn in the opposite direction is necessary for all speeds, it’s more noticeable at high speeds, which is why decreasing velocity for a tighter turn in a good idea. But, if you decrease the speed too much, momentum will be lost (to friction) and the bike and rider will fall over.
Given that this is true (and I believe that it is) I wanted to test some other aspects of leaning versus steering control. I found that leaning is necessary to alter your course by small angles, when traveling on a relatively straight path. However, for 90 degree turns, simply leaning is not going to get the job done.
I tried to simply turn the front wheel via the handlebars in the direction I wanted to make such a 90 degree turn, while traveling a straight path. I noticed that I soon as a turned the handlebars even slightly I felt the bike start to tip. Almost immediately following that, however, the back part of my bike seem to “catch up” with the front wheel, causing me to continue on a straight path.
My question is if this is some physical property (perhaps my momentum?) which makes the bike want to continue on a straight path, or is it some unconscious steering on my part? I assume it has to do with the repositioning of the center of mass, so that the bike doesn’t tip, but is this because I don’t want it to tip, or because the bike can’t physically tip when traveling forward at a significant velocity?
What I find interesting, as well, is that it is impossible to turn without first steering in the opposite direction of the turn and then leaning to make the turn. This seems to be the only possible way to reposition your center of mass in order to make a successful turn. Is this also true?
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