# Physics of cornering - Bike Racing

Discussion in 'Physics' started by TehYoyo, May 3, 2014.

1. ### TehYoyo Thread Starter New Member

Apr 20, 2013
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I'm a competitive road cyclist and a high school student in 1st-year Physics (Equivalent to AP Physics B). I was hoping for some help on how to develop my cornering technique when racing.

As I understand cornering:
There are four forces acting on the rider (me) when I corner.

One would be the force of gravity, pointing downwards, constant.
Two would be the normal force, pointing upwards (perpendicular to surface), equal to the force of gravity
Three would be the centripetal force, pointing toward the center of the curve (road curve, circle, etc), equal to (v-subc)^2 over r.
Four would be the force of friction, pointing outwards, (is this next part right?) equal to the centripetal force.

My goal is to take corners faster. So, I need to increase my velocity (v-subc) while maintaining the same radius r.

How do I do this? Online there's a lot of talk about center of gravity, bike centerline, etc, but that's where I get confused. If someone could talk me through it, I'd be really grateful.

2. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
519
Hopefully you are also here out of an interest in electronics?

First thing to note.

You are not in equilibrium when cycling.

The centripetal force is a real force and is provided by friction.

It is not, as it would be in an equilibrium analysis, equal and opposite.

There is a recent questiion about exactly the same thing here.

http://www.scienceforums.net/topic/82943-moments-at-contact-tyre-patch-and-wheel-spindle/

3. ### BR-549 Distinguished Member

Sep 22, 2013
2,999
724
Just a thought. Don't turn the full 90 degrees. Come into turn wide, turn 45 degrees. Try to accelerate thru this turn. Now, accelerate in straight line thru curve. Come up wide and turn 45 degrees to complete turn. Make your turns...45 degrees....then straight,.....then 45 again. Haven't been on bike for long time. See if this decreases your lap time.

4. ### joeyd999 AAC Fanatic!

Jun 6, 2011
2,964
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Ideas:

-- Put "stick'em" on your tires -- or cleats (don't run over anyone!)...

5. ### wayneh Expert

Sep 9, 2010
13,435
4,273
There is an excellent book called "Bicycle Physics" that might interest you despite its focus on bicycles.

The limiting factor is friction - a loss of friction is a fall. Think about increasing friction. It's all about that little patch of tire gripping that little patch of road. Without changing the road or the tire, all you can do to increase friction is to push down harder on the tire.

Downforce on the tire is helped by moving the center of gravity lower, so that in a lean, there is more weight over the the contact point. I think you lean less if the COG is lower also?

6. ### THE_RB AAC Fanatic!

Feb 11, 2008
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I'd disagree with that. The lean is a natural balance between the cornering g force and gravity. The height of the centre of mass of the bike shouldn't matter, provided it remains on the centreline of the bike.

What would help is to move the centre of mass inward toward the centre of the curve, like hanging off the bike.

7. ### wayneh Expert

Sep 9, 2010
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I was picturing this sort of thing. To me it looks like the rider's position is more about lowering his COG, in part to allow the bike to remain more upright, and less about moving it towards the center of rotation. But it is obviously shifted in both directions.

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8. ### THE_RB AAC Fanatic!

Feb 11, 2008
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It's shifted in both directions, but the one that helps the cornering effect is moving it to the side of the bike's centreline.

9. ### alfacliff Well-Known Member

Dec 13, 2013
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also, braking can get the weight shifted to the front tire to compensate for increasted thrust trying to lift it.

10. ### wayneh Expert

Sep 9, 2010
13,435
4,273
There's an enormous body of literature on this and classical physics are just part of it. Necessary but not sufficient, you might say. It gets complicated quickly when you introduce wheels with different geometries front and rear, use counter steering, and so forth.

I think the off-axis lean in the picture is to achieve a more aggressive lean while maintaining a clearance for the bike itself - so it doesn't scrape metal - as well as to maintain better suspension function. The suspension can only move in the vertical axis (relative to the bike's geometry). Keeping the bike more upright means better traction as small bumps can still be absorbed.