# The difference between rear and front brakes of a bicycle

1. Nov 10, 2008

### Kimusubi

Hi,

I'm a sophomore student at Arizona State University studying Aerospace. I'm currently taking my first physics class ever and I'm loving it. Although there isn't enough calculus, it's mostly formula based, so it's a bit disappointing on that end. Anyways, ever since I started taking the physics class, I've become curious on how certain things in the world work. I mountain bike a lot, so recently I started thinking of how the front and rear brakes differ from one another. By that I mean, why does it take longer for the bike to stop when using the rear brakes versus using the front brakes when you are moving forward, and vise-versa when you are moving backwards. And also why is there a tendency to fly forward when using the front brakes. I asked this of my professor, and he wasn't able to give me an explanation on it, and told me that he would get back to me. I mean, I understand why it happens (in the most common-sense non-physical way), but I was wondering if anyone could explain this to me in more of a scientific way. Does it have anything to do with Newton's laws, or is it because of center of mass, or some other reason? If anyone can give me a detailed explanation of this, I would really appreciate it. But just keep in mind that this is my first physics class ever, so if you're trying to explain something a bit more advanced, please break it down for me. Thank you all in advance for your contribution.

- Ali

2. Nov 10, 2008

### Danger

Welcome to PF, Ali.
The effectiveness differs because of weight transfer. Whichever way you're going, the leading wheel will be pressed into the ground harder, while the trailing one loses traction.

3. Nov 10, 2008

### Kimusubi

Oh ok, that seemed simple enough. Now, when a person is going at a fairly high speed, uses the front brakes to come to a sudden stop, and ends up flying forward, is that because the translational acceleration is changed to angular acceleration or is it because of torque?

4. Nov 10, 2008

### Danger

That's simply Newtonian physics rearing its ugly head. Your body doesn't want to stop when the bike does, because its momentum tries to carry it forward. The same basic thing happens when both brakes are used, but when you use only the front one, the rear of the bike also wants to continue forward and will pivot over the front.

Last edited: Nov 11, 2008
5. Nov 10, 2008

### Kimusubi

Awesome, thank you so much for your help!

6. Nov 10, 2008

### Danger

You're more than welcome. Others here can give you more detailed answers, with formulae if you wish, but that's a bit beyond me.