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Q & A: Why Do Cyclists Tilt When Turning?

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Most recent answer: 02/09/2013
Q:
why the cyclists do tilts while taking the turn in circular path?
- Ispal pun (age 18)
nepal
A:

Interesting question, Ispal.

The reason cyclists tilt when they go around turns has to do with balancing torques on their bike. The angle that they tilt at is the specific angle at which the torque from the upward normal force on their tires by the road is of equal magnitude/opposite direction of  the torque applied by the inward frictional centripetal force on the bottom of the bike that comes from the tires turning the bike into the turn. I have attached a diagram to show this better.

(Picture courtesy of )

We can ignore gravity if we take the fixed point of the rotation to be the center of mass. The reason these torques can be balanced just by tilting is because any given torque is dependent upon three things:

1. The magnitude of the applied force - which in this case is constant for both the normal force and centripetal friction force.

2. The distance away from the fixed point of rotation - in this case the friction and normal force are acting on the same point, so there isn't anything complicated to consider there either.

3. The angle between the force and the object it is being applied to - this is the only thing we have left as a variable in order to balance the torques, hence tilting to go through a turn smoothly!

Of course, a biker doesn't have to really think about all that to turn correctly. If the angle is too small then the biker will start to fall towards the road in the direction that they're turning in. If the angle is too large then the biker will start to be pushed out of the turn until they lose balance and fall in the opposite direction of the turn. The biker will feel it if either one of those start to happen, and instinctively knows to correct it by adjusting their lean.

Samson.


(published on 02/09/2013)

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