Everyone knows how a bike stays upright — the gyroscopic forces induced by the spinning wheels, and the “castor effect” created by trail. Or do they? A team of engineers says it's proven that bikes can stay upright even without these things.
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While it’s been generally accepted for decades that they are the two factors keeping your bike upright, English-born engineer Jim Papadopoulos and his colleagues suggest that a bike will be stable even if these two forces aren’t present.
Papadopoulos believes that two well-accepted studies from the 20th century on the self-stability of bikes contain mistakes. He's been working with an international team of four engineers (J.D.G. Kooijman, J.P. Meijaard, Andy Ruina and A. L. Schwab) to prove in the real world that a bike is self-stable even without the influence of these two forces. To cancel out the gyroscopic effect, they used counter-rotating wheels on a test-bike, and to eliminate the stabilising effect of trail, they made the trail negative.
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“Our work,” says Papadopoulos, now an assistant teaching professor at the Northeastern University in Boston, “was about finding the correct equations and proving that widely accepted assertions were not precisely true. Therefore, we encourage designers to play with formerly forbidden limits like negative trail and vertical steering. This is not necessarily better, but neither should they assume it must be worse.”
So what exactly are gyroscopic forces and fork trail?
The gyroscopic effect is the tendency of a spinning wheel to resist tilting. In fact, it’s a little more complicated than that: when you attempt to move a spinning wheel in one dimension it will exert a reaction force that tries to move it in a different dimension. In 1910, the mathematicians Felix Klein, Fritz Noether and Arnold Sommerfeld wrote a four-volume book on gyros, in which they argued that the gyroscopic effect is what causes a bike to be self-stabilising in motion.
What else might be helping your bike stay upright when in motion?
The slow pace of change
Some new designs
You can read more at BikeRadar.com
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