Why are bicycles more stable when they are going faster?

Question

Why is it hard to keep the bike upright when standing still and effortless when going forward. And the faster you're going the easier it becomes.
I don't see why angular momentum, angular acceleration, or speed would affect that.

Answer 1

Nothing to do with angular momentum.

If you weight the rims of the wheels of a bike to increase the angular momentum so that the wheels behave like a gyroscope (bike wheels are really light usually), the bike becomes almost impossible to ride.

A bike stays upright because the centre of gravity at the front wheel is slightly behind where the wheel touches the ground (the bike forks bend forward). Because of this, if the bike tips to the right the front wheel turns to the left and vice versa.

If the bike is stationary this does not help a lot.

But if it is moving forward this tends to steer the bike out of toppling in the direction of lean, and this helps you to balance the bike ( a bike with no rider always falls over - its your sense of balance that keeps it upright).

The fast the bike goes, the more pronounced the self correcting steering is.

PS bikes have been made with the forks bent backwards so that the self steering is in the direction of lean, so exaggerating a loss of balance -it is hysterical to see someone try to ride this sort of bike

Answer 2

The faster you are going the bigger your momemtum is (product of mass and velocity). Momentum is a vector, that means it has a direction. The only external force that acts on you is gravity. This is a constant at the product of your mass and the acceleration due to gravity (mg). The gravitational force (as any other force) is also a vector. The only thing that can change momentum is external force. When you are moving slowly or standing still your momentum is either small or zero so it is easy for gravity to change your momentum, for example instead of moving forward gravity can change your momentum and make you fall sideways. But as you pick up speed your momentum grows. The force due to gravity however remains the same. So it becomes harder for that force to push you over.

I have tried to explain in very lay terms but I think you are conversant with science already so please don't be offended, I am not trying to be condescending. It's simply the fact that I can't draw a vector or write an equation on this forum.

Answer 3

Momentum is the tendancy of an object in motion to continue moving in the same direction.

Angular Momentum is the tendancy of an object to keep rotating around the same axis. The faster the speed of the bike, the higher the angular momentum of the wheels around the axels of the tires. This angular momentum reduces the tendancy of the bike to tip, which would be a rotation around an axis in the direction of the bikes movement.

Answer 4

yes it's a matter of inertia. I think it works like this: you have a momentum/velocity when the bicycle is moving therefore when syou aplly a force 2 things can happen the force can be in the same direction, in that case it will acelarate you or decrease your velocity, if it is perpendicular you can talk, you can interpret it has a centrific force (don't know if this is the name in english) this force will be proportinal to v^2/R where v is your velocity, and R is the radius of the turn that you will make if v is too small you have to got a R small to compensate also this is the same has to say that you turn too much the bicicle drops on it self and at the end you drop, if v=0 you can't talk about this force at all and the only option is to fall.

Answer 5

Because our earth is round, moving faster will cause more centrifugal power.

Answer 6

It's inertia and the flywheel effect from the wheels.

Answer 7

He nailed it. What's in motion tends to stay in motion.