Can someboby please explain to me why it is better for a bicycle/ motor cycle to have lower center of mass when it rounds a turn. What I could gather from the rule I = mr2 Was that the arm is shorter so less moment of inertia but what does that have you do with doing a better turn


1 Answer 1


It is not helpful to consider the moment of inertia of the bike about its centre of rotation. All you need to consider are the forces on the cyclist/biker. The centripetal force from the friction of the tyre on the road $mv^2/r$, together with the inertia of the cyclist and bicycle form an overturning couple. (These can alternatively be considered as frictional reaction and centrifugal force respectively). This couple is balanced by the one from the weight and the vertical reaction (presuming the cyclist is leaning into the turn).

If the centre of gravity is lower, the overturning moment will be correspondingly less and that is preferable. However, it should be pointed out that, if the angle of lean is the same (and the velocity and radius of turn), the bicycle will be equally well balanced with a high C of G because both couples will increase by the same amount. However, the same cannot be said of a car, where resistance to overturning is maintained by the fixed horizontal distance between its centre of mass and the outer wheels, so there is no question that a low centre of mass is desirable for a car driving on a bend.

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