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© Copyright 1998, Jim Loy
Why doesn't a bicycle fall over? I know, it does fall over, but less often than one would expect. Some physicists will tell you that it is the gyroscope effect of the tires, which tend to prevent the bicycle from changing the angle of its tilt. There is a strong gyroscope effect going on here. But, that is not the major reason bikes don't fall over. If you are leaning at a 45 degree angle, the gyroscope effect will tend to keep you at that 45 degree angle. It will not straighten out the leaning. You will just fall over, slower.
Of more importance is that when a bicycle leans to the right, it tends to turn to the right. You can make a fairly good turn, without ever turning the handle bars, just by leaning. This effect is used by those riders who ride with no hands. This effect is caused by the fact that the wheels are not cylinders. When you ride straight and upright, the wheels do act like cylinders. But, when you lean to one side, the wheels act like cones, and turn in the direction that you lean.
But, the most important effect is that when you are leaning right, you can straighten up the leaning of the bike by turning the bike. You adjust the amount of leaning by turning the handlebars. This is the main reason that a bike stays upright. And you often don't even have to turn the handlebars, to adjust the leaning.