Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Linda OCarroll on 06/01/2010 10:30:02
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Linda OCarroll asked the Naked Scientists:
Hi Chris
Another question from Diana's mum:
How does one really balance on a bicycle? It feels easy but looks impossible when you've never tried it. Why is it that as soon as you try to think about how you are cornering on a bicycle, you fall off, but if you don't think about it you don't fall off? Which bit of you is the sort of fulcrum of balance sort of thing? It feels as if it's your waist - but is it?
Linda O'Carroll.
What do you think?
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This might help:
Why does a bike stay up so much more easily when it’s moving? It’s very hard to balance when the bike isn’t moving. Jim
Dave - It is very hard to balance when a bike’s stationary. There’s two effects. One of them is if you tip a bike to the left you’ll see the front wheel tends to turn into the left as well because the front forks are leaning forwards. It’s more stable if the handlebars tip to the left. Once the handlebars tip to the left then you tend to steer into the corner and the wheel works its way back underneath you.
Chris - So it’s like if I give you the old trick of a broom handle you can balance the broom handle in the palm of your hand. Just by moving your hand around you can hold the broom handle vertically. It’s because when the broom starts to fall in one direction you can move your hand to go effectively into the direction of fall and that’s what keeps it stable. The bike’s doing the same thing.
Dave - The bike’s doing the same thing automatically. There’s also a gyroscopic effect that can help.
Chris - Because the wheels are spinning and so because the wheels themselves are turning they have a gyroscopic moment. It’s obviously difficult to make it deviate. Given that it’s most unstable when it’s moving slower you can still balance. You probably get more stable when you speed up?
Dave - You do and it’s easier to ride when you’re going faster. If you imagine a spinning top it starts to fall over it starts to rotate round and round in circles and the same thing starts to happen to your bike wheel. As you start to turn over it starts rotating and turns into the corner as well.
January 2009
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The most important part of generating stability in a bicycle while it is moving is the shape of the forks that hold the front wheel. if you look carefully at the forks you will notice that the front wheel is pivoted so that it is slightly in front of the line drawn down the fork tube and the fork tube slopes upwards and backwards from the direction of forward motion. This means that when the bicycle is loaded and moving forwards and it tilts slightly to the left the front wheel tends to steer slightly to the right and correct this tilt. This effect gives you feedback into your hands on the handlebars and helps you keep upright. It also allows you to ride a bicycle with no hands on the steering and steer the bicycle as well. If one builds a bicycle with the opposite effect it is almost unridable because it is so unstable and the feedback is in the wrong direction. On some bicycles it is possible to turn the handlebars through 180 degrees and ride it with the handlebars the wrong way round. this will create this wrong feedback effect.