# I Way the cornering forces are felt when riding a motorcycle

1. Dec 19, 2017

### Erunanethiel

Everybody says when going around a corner on a motorcycle and leaning, you feel the g forces vertically (like pushing down on your spine) as opposed to horizontally when cornering in a car.

I can't understand how that can be the case, if the rider corners at 45 degrees, the gravitational force will perpendicular to the ground, and the centrifugal force will always be parallel to the ground, no matter the amount. So how can the rider feel it pushing him down to the seat?

As for the amount of force that is felt:

If the rider is cornering at 0.5g, does he only feel 0.5g on his body? The total force he feels is less than 1g which is what he feels when standing on still on the ground?

2. Dec 19, 2017

### lekh2003

You don't feel the g-force. You feel a force very similar to gravity and kind of feels like gravity but isn't. This is centripetal force (centrifugal force doesn't exist, that is a myth). The centripetal force is acting on the bike towards to the point of rotation.

To answer your problem, think about which direction the bike is being pushed by the centripetal force. You are at 45 degrees and spinning in a circle. If you think about it, the centripetal force is acting at an angle. According to Newton's third law, the bike exerts a force on you and you feel the force on your spine.

The force you are feeling is not entirely the g-force. You might feel some of it, but most of it is a result of the centripetal force pulling the bike inwards and keeping you in rotation.

I'm not an engineer or mechanic so I might give a misconstrued opinion. Take a look at this link:

https://www.wired.com/2015/09/just-far-can-motorcycle-lean-turn/

3. Dec 19, 2017

### Erunanethiel

I am confused

4. Dec 19, 2017

### lekh2003

5. Dec 19, 2017

### Erunanethiel

I searched "how do motorcycles lean so far without tipping over" on google and read the first link, hope it is the same one. Even though I read and understood it, I still don't get what force the rider feels when cornering.

6. Dec 19, 2017

### lekh2003

Yes, I think it is the same link.

When a rider is cornering, he leans over, so the article explains the physics behind that (leaning over). When you study physics you are introduced to the centrifugal force, but this is actually the centripetal force. The bike is being pulled to the center of rotation by the centripetal force. Friction, the banking of the bike and you are acting in opposition. If you were to suddenly jump off and the road lost friction, then the bike would rush towards the corner due to the centripetal force.

What I am giving as an explanation pales in comparison to the link. Make sure you understand all the concepts in the link, there is no more I can provide you with.

7. Dec 19, 2017

### Erunanethiel

Doesn't the centripetal force push the system "out" while gravity is pushing the system "down" towards the ground?

8. Dec 19, 2017

### lekh2003

See, this is the misconception I am trying to resolve. You are still under the assumption that there is a force pushing you outwards. There is no such force acting in any way. Try swinging an object held on with a string. Let go of the string and the object maintains its velocity. You let go of the string which was the centripetal force and then there was no force on the object. If this magic force was actually there, then the objects would fly outwards, but it doesn't.

In this situation, there is a centripetal force which pulls the bike inwards. The equal and opposite force is the feeling that you are pushed down. Gravity is acting, but so is the centripetal force.

9. Dec 19, 2017

### Erunanethiel

Isn't the centripetal force in the "swinging a ball attached to a rope" analogy provided by the string? And in the case of the motorcycle, it is provided by the tires, and if the tires lost friction, the motorcycle would continue in a direction tangent to it's previous path right? Rather than going towards the corner as you said. I have a feeling I am missing something, thanks for helping out

10. Dec 19, 2017

### lekh2003

Yes, it would continue at a tangent, sorry, I made an error.

Again, just read the article. It explains everything better than I ever can.

11. Dec 19, 2017

### Erunanethiel

These are all very confusing subjects for us mere mortals, I wish I was Newton or something so I could think myself out of the questions I think about

12. Dec 19, 2017

### lekh2003

You don't need to be Newton to understand this. You just need to study physics from the ground up. You will understand these concepts much better if you start learning about motion, then Newton's laws, then rotation, uniform circular motion and then you will be able to solve your bike problem on your own.

I suggest that you look up some course-site and take a course in basic classical physics. It will help with understanding mechanics.

13. Dec 19, 2017

### Erunanethiel

Thank you, I have big exam in 6 months, after that I will do so

So, the centripetal force is pushing us inwards at 1g, and at 1g the system must be leaning 45 degrees, so if the force the rider feels is the centripetal force, it must be parallel to the ground, but the rider feels the forces "head to toe" how does that happen?

14. Dec 19, 2017

### jbriggs444

In the case of a motorcycle on a curve, the centripetal force on the motorcycle is provided by the road on the tires -- friction. The road supports the tires against the downward force of the motorcycle due to gravity. The road provides the inward force that provides the acceleration toward the center of the curve.

The total force from the road consists of those two components. One pointing inward and one pointing upward. Those forces add as vectors. The result is a single force pointing diagonally up and in.

The force you feel on the seat of your pants is very much the same. Diagonally upward and in. But the bike and rider are also leaning diagonally upward and in. The force is directly aligned "under" the seat of the pants. So the force feels like an ordinary upward force. It's just that "up" is leaning in.

15. Dec 19, 2017

### Erunanethiel

If the rider is cornering at 0.5g, does he only feel 0.5g on his body? The total force he feels is less than 1g which is what he feels when standing on still on the ground?

16. Dec 19, 2017

### jbriggs444

If you add 0.5 g inward to 1.0 g upward using the Pythagorean theorem, what do you get? That's what's pushing on the seat of your pants.

17. Dec 19, 2017

### Erunanethiel

I don't know

18. Dec 19, 2017

### jbriggs444

Do you know how to add vectors?

If you walk 1 mile north and 0.5 miles east you could have cut the corner and walked directly to the endpoint along the diagonal. Pythagoras gave us a formula for the length of that diagonal.

Can you tell us how long that diagonal would be?

19. Dec 19, 2017

### Staff: Mentor

Wait a minute. You said in one of your other motorcycle threads that you ride. Why are you having to ask this question?

20. Dec 19, 2017

### Erunanethiel

Because I don't feel any g forces what so ever when cornering, maybe because I dont lean enough