# As easy as riding a bike

• lavalamp

#### lavalamp

Simple question really, why is it easy to balance on a bike when you are moving fast but hard to balance when you are going slowly or are stopped?

Originally posted by lavalamp
Simple question really, why is it easy to balance on a bike when you are moving fast but hard to balance when you are going slowly or are stopped?

Because of several effects, the main one being the conservation of angular momentum. Read here:

http://www.physicscentral.com/lou/lou-01-1.html

Zz.

The automatic steering occurs for two reasons. First, there is gyroscopic precession that occurs when the spinning front wheel experiences torques from the ground. When the bicycle tips to the left, forces from the ground twist the spinning wheel so that its angular momentum shifts from leftward to rearward. This complicated precession effect causes the wheel to steer left toward the left.
I don't quite get this paragraph, could you clear it up for me please.

I understand the rest of the article, I just don't know how a gyroscope works, what a gyroscopic precession is or why the front wheel experiences torques from the ground.

I am not even sure that I understand what that paragraph says.

I do know this from personal experience. When riding on my bike with no hands on the handle bars if I apply a very gentle pressure to the end of the right handle with my pinky finger the bike immediately leans to the RIGHT and the front wheel eagerly follows to the RIGHT, thus I have initiated a turn to the right by pushing on the right handle bar.

A spinning bike wheel is a form of a gyroscope, it is the gyroscopic forces generated which make it POSSIBLE to ride a bike. If you do not already have one find a toy gyroscope and explore the forces generated when it is spinning.

heres an even odder one, why does a top not fall over when its spinning?

as for that paragraph, it means that when the bike leans over to the left, the ground turns the front wheel left and causes the bike to turn left, this cause a change in momentum as the bike accelerates to the left and this change in direction pushes the bike over to the right. So it means that the bike, when in motion, is self correcting. The top i understand visually how it corrects itself, but I am not going to explain that one.

should we confuse him more by telling him about the whole "turn right to go left" thing on a bike?

Originally posted by Gara
should we confuse him more by telling him about the whole "turn right to go left" thing on a bike?
Didn't revesz just cover this one?

Originally posted by lavalamp
Simple question really, why is it easy to balance on a bike when you are moving fast but hard to balance when you are going slowly or are stopped?

A bike is not stable. Stand it up by itself and it will fall over. Whether you are on it or not, it will fall over (not quite true if your really skilled, but pretty close to true). There's no mystery. But when it is moving, you subconciously steer to correct balance. That's all there is to it. All discussions of gyroscopes are beside the point. The gyro provides a means of allowing steering inputs to correct balance, but it's not even the only one.

An analogous situation is standing on one skate. It's hard to do without hopping around. But if you're moving forward on one skate, balance is no problem.

"Didn't revesz just cover this one?"

no, he did not. he said if a bike leans left the bike turns left.

i was saying about turning right to go left.

Originally posted by Gara
"Didn't revesz just cover this one?"

no, he did not. he said if a bike leans left the bike turns left.

i was saying about turning right to go left.

I think we are all pretty clear that you can turn right 3 times instead if you want to go left.

no, i mean that if you want to turn left on a bike moving at speed, the best way to take that corner is to slightly turn the handlebars to the right. this makes the bike lean left. then, to go back up, turn left, this will pull the bike up again. I am sure some one else can explain it better.

Originally posted by Gara

I am sure some one else can explain it better.
No, you did just fine. A wordier explanation is http://www.triumf.ca/people/baartman/bike/steering.html [Broken]

Last edited by a moderator:
Originally posted by Gara
im sure some one else can explain it better.
I like your version a lot more. The Rake and Trail paragraph was terrible.

I had always wondered why dirt bikers turned into corners the wrong way, now I sort of know.

The reason you turn left to go right and vice versa is the following: Think about driving down the road in a car, you turn right and the body of the car rolls to the left and puts it's weight on the left tires. Think back to a bike. You turn right and the body of the bike falls left. Therefore when (at speeds above 10mph)you want to go left push the handlebars right to get the bike to lean and then follow up by leaning in that direction. The bike will pull that way. It's a lot more natural when you are on the bike, it sounds weird when trying to type it out.

Also the gyroscopic effect has a lot to do with the way the bike stays up right. If you don't believe so do this little experiment. Get an old bike wheel and tire. The wheel must still be on the axle. Now hold the axle with both of your hands and get a buddy to spin it hard while you are holding it out striaght. Now try to tilt the tire and wheel. It will want to go back up stright and will be hard to tilt. Also like when you roll a penny and it doesn't fall over until its slowed down...