[sendler]

Here we go with another "just ride the thing" topic and why you can corner with greater lateral acceleration, or preserve more safety margin in the rain, by hanging your body weight off of the bike to the inside. The physics of cornering on a bike (lateral acceleration) are pretty complex and believe it or not, are not accepted in total agreement even to this day.
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Bicycle and motorcycle dynamics - Wikipedia, the free encyclopedia
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Camber thrust - Wikipedia, the free encyclopedia
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One stated fact, as a bike is leaned it's trail is decreased, immediately makes sense. Less trail, less stability. Easier to fall from a slight mis correction. There may also be a trade off in efficient use of the contact patch for cornering during the transition from slip angle of a steered wheel at more straight up and down attitudes, to camber thrust of a leaned wheel. Interesting?

 

[sendler]

Tire width

Tire width also comes into play. The contact patch of the tire is shifted to the inside of the turn with increasing lean angles making the radius of the turn a few inches tighter than it would be if the tire were straight up and down.

 

[sendler]

Patch track length

It also seems that with greater lean angles comes a greater discrepancy in the track length that the contact patch sees between the inside edge and the outside edge of the patch due to the differing radii that each area is tracking which wastes grip with non beneficial twisting forces.

 

[hunkyleepickle]

Are you talking to yourself again?

 

[Rick]

contrary opinion, leaning does not increase traction

Here we go with another "just ride the thing" topic and why you can corner with greater lateral acceleration, or preserve more safety margin in the rain, by hanging your body weight off of the bike to the inside. The physics of cornering on a bike (lateral acceleration) are pretty complex and believe it or not, are not accepted in total agreement even to this day.
.
Bicycle and motorcycle dynamics - Wikipedia, the free encyclopedia
.
Camber thrust - Wikipedia, the free encyclopedia
.
One stated fact, as a bike is leaned it's trail is decreased, immediately makes sense. Less trail, less stability. Easier to fall from a slight mis correction. There may also be a trade off in efficient use of the contact patch for cornering during the transition from slip angle of a steered wheel at more straight up and down attitudes, to camber thrust of a leaned wheel. Interesting?

I might be one of the few members here with both an interest in this subject. So, just for the entertainment and enlightenment of our fellow riders, let me take the devils advocate position..
I mean no offense, and don't take this as a personal argument, I hope to learn something by testing my theories as well..

1. You said "you can corner with greater lateral acceleration, or preserve more safety margin in the rain, by hanging your body weight off of the bike to the inside." But did not say why?
Lateral acceleration is limited only by friction. The formula for friction is Friction = (coefficient of friction) * Weight. Lets call that coefficient 'mu' cuz thats what the engineers do. So, say "F=mu*W
Assuming some moment in time, weight on both tires is constant, and leaning does not change this distribution (does it?).
Only way to increase F is to increase the friction by getting stickier tires. Leaning does nothing.

The Camber thrust issue you mentioned is for cambered tires forced to travel IN A STRAIGHT LINE, and is not applicable to our discussion.

 

[Rick]

Tire width also comes into play. The contact patch of the tire is shifted to the inside of the turn with increasing lean angles making the radius of the turn a few inches tighter than it would be if the tire were straight up and down.

There is one and only one lean angle for every turn radius and speed. Too much lean and you'll fall in, too little and you'll fall to the outside of the turn. Typically we riders choose our entry speed and our radius (within the limits of the road), the lean angle is the RESULT we must skillfully produce to maintain that line.
Leaning in does reduce the turn radius, but again, we are limited by our tire traction. There is no free additional traction gained by leaning.

 

[Aufitt]

Just do some advanced rider training courses and read Keith Code.

You are confusing the hell out of yourself and maybe many new riders.

 

[Rick]

It also seems that with greater lean angles comes a greater discrepancy in the track length that the contact patch sees between the inside edge and the outside edge of the patch due to the differing radii that each area is tracking which wastes grip with non beneficial twisting forces.

Agreed!
No matter what the lean angle, radius of curve, or speed, the contact patch is the same size. It is a flat spot on the tire proportional in size to tire pressure and bike weight (on each tire).
But yes, leaning the bike on our round tires moves the oval patch farther to the outside of the tire, and the smaller the turn radius (greater lean angle), the larger the difference in turn circumference 'seen' by the outside and inside of the contact patch. This is the 'scrubbing' we can see and hear on car and (especially) truck tires as they negotiate a tight turn at slow speed.
Any portions of the tire which are literally 'scrubbing' (sliding along the road) as opposed to rolling on it, are now operating at the coefficient of sliding friction, which is less than the coefficient of static friction (which is higher). Thus the overall average coefficient of friction is lower, and so is the resultant available friction.

 

[sendler]

Loud

Are you talking to yourself again?

I prefer to call it thinking out loud.

 

[sendler]

Agree

The Camber thrust issue you mentioned is for cambered tires forced to travel IN A STRAIGHT LINE, and is not applicable to our discussion.

Every object which is in motion is forced to travel in a straight line by Newton's laws so camber thrust is an important portion of the centripetal force which makes the bike corner. Along with slip (steering) angle which is more dominant for cars.
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The available area of the tire patch may be about the same for a perpendicular tire and a leaned tire but it's efficient utilization may be different due to the twisting, scrubbing forces which develop in a leaned tire due to the greater distance the outside of the patch has to travel compared to the inside. And the shape of the patch may change. This will waste some of the available friction but may actually peak quite early with increasing lean angle. Not sure. It is fascinating to me that in this modern age, science is still somewhat baffled by the physics of a motorcycle turning.
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A leaned tire with width ( all real tires) is forced into a tighter radius turn as the patch moves in. Again, a minimal percentage of change relative to the radius of the corner but still indisputable.
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True, the total lean angle of the bike and rider for any given corner and speed is the same. The difference you can make is by changing how much of this comes from the bike and how much from the rider. If the rider is hanging off of the inside of the bike, the bike will be leaning less. Racers don't do this just to look cool. Hanging off of the bike allows you to go faster around a corner. Or, keeps you that much further away from sliding past the limit when cornering in the rain. More margin for safety.
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Trail makes a bike more stable. Less twitchy. Trail is lost as the bike is leaned. The more straight up the bike, the more trail.
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Agreed!
Any portions of the tire which are literally 'scrubbing' (sliding along the road) as opposed to rolling on it, are now operating at the coefficient of sliding friction, which is less than the coefficient of static friction (which is higher). Thus the overall average coefficient of friction is lower, and so is the resultant available friction.

You have agreed with me here. There is more to this that I can easily feel on my mountain bike in slippery conditions. But I haven't yet found any further good documentation. A perpendicular tire uses it's patch better than a leaned tire.
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There must be other factors at work not yet discussed. Are the force vectors from gravity on the patch really the same?
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Hanging off of the bike gives much more margin for safety when cornering at the limit on the track or on a wet street. It should be practiced until comfortable along with all of the other riding skills

 

[ice_burg]

MY .02 is simply that you have more downward force on an upright tire than you do a leaned tire... Gravity is more on your side when you are straight up than it is when you are leaning the bike. I think the body weight of the person hanging off of the bike in the middle just allows for a tighter pivot point of turning while keeping the bike more upright and under the superior force of gravity rather than introducing a situation where gravity is more against you than it is for you. I am no expert but this what it seems to me in my seat of the pants understanding.

 

[Kurlon]

When I race in the rain I hang off more in the corners than I do in the dry despite a lower overall corner speed for two reasons:

1) Bigger contact patch with the bike more upright. I want that rubber on the road dang it!

2) I'm in a better position to use my knee to 'lever' the bike putting more pressure on the rear tire should it decide to get squirrely.

When I ride on the street in the rain, I just don't corner that fast.

 

[sendler]

Video

There is an excellent slow motion close up of the tires tracking a high speed sweeper in the Aragon moto GP video.
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