Cornering 101

Headquarters Air Mobility Command

Enabling the “Global” in “Global Vigilance, Reach and Power!”

Cornering 101

2Enabling the “Global” in “Global Vigilance, Reach and Power!”

The information presented here is for informational use only

• Many references were used to develop this presentation

• Not all possibilities are covered

• Use the given information with proper respect to ORM

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FOR OFFICIAL USE ONLYNote: This Slide is Mandatory


Forces acting on a motorcycle in a corner Suspension / Chassis dynamics Basic cornering physics Negotiating corner

OVERVIEW


Forces

General Theory• Motorcycle turns via deflection of front wheel/tire

Makes motorcycle lean opposite path of wheel/tire Motorcycle actually moves opposite intended path first

• Tires/corner effective radius becomes smaller Styrofoam coffee cup on its side Variable depending on many factors

• Gravity, centrifugal force Gravity pulls down, centrifugal force pulls outside, state of

equilibrium Centrifugal force must overcome gravity pulling down

the amount the combined mass is leaned over Limited by traction available through co-efficient of

friction between tires and surface


Forces

Motorcycle and rider are independent of each other with same forces

• Combined of the two is motorcycle/rider

• Can be adjusted by rider more easily than adjusting of motorcycle

• Forces are at equilibrium point of the contact patch of the front and rear tires


Forces

Rider / Motorcycle Centrifugal

Rider / Motorcycle equilibrium point Earth Gravity

Combined CG


Chassis Dynamic

Chassis• Rake, is the angle formed by:

Line drawn from center of steering head through tire to ground

Vertical line drawn through center of front wheel axle Rake determines steering response

• Trail is: Distance between vertical line through front axle Line drawn to the ground from center of steering head Trail determines moment of self-righting (straight-line

stability)

• As suspension compresses on fork-equipped motorcycle, effective rake and trail get smaller, thus steering quickens stability decreases


Chassis Dynamic

Chassis:• Rear suspension comprised of swing arm, torque arm,

chain pull Line through all three comprise pole of moment (PoM) Swing arm comprised of wheel and pivot location Torque arm usually attached to brake caliper

Maybe a rod to frame Maybe rod to swing arm or large caliper mounting plate

Chain pull is line made through the top of the chain Angle produced by all three determine effect of

compression under braking and extension under acceleration

Larger torque arm angle, less compression during braking Larger chain pull angle, greater extension (lifting) under

acceleration


Chassis Dynamic

Wheelbase Effect of wheelbase determines diameter of the turning

radius a motorcycle may have Shorter allows for smaller turning radius


Chassis Dynamic

Single track vehicle is unstable

• Gyroscopic force created by turning wheel/tires creates stability Greater the speed, greater the stability Larger the diameter, greater the stability

• All chassis and suspension dynamics affect amount of force needed to move stability created by turning wheel/tire combination


Chassis Dynamic

Steep, small, short Gradual, large, long

Rake, Trail, Wheelbase

Agile Less Agile


Review

Key points:• 3 forces acting on a motorcycle when cornering

• Less rake mean quicker steering

• Less trail less self righting

• Acceleration causes back to rise All can vary and must be controlled by rider• Weight transfer under braking and accelerating changes

suspension geometry, thus changing M/C attitude

• Centrifugal forces keep suspension compressed through corner Changing centrifugal forces when cornering changes

motorcycle attitude Constant centrifugal force keeps suspension stable


Examples

Compression

Extension


Cornering Physics

Tires

• Ffriction= f x C f is theoretical coefficient

of friction whose max value is 1

C is vertical load bearing on the wheel

• Represented by the cross of X and Y

• As long as tire’s contact pitch-black oval) has some part on top of the intersection, friction (traction) is available

Y

X


Cornering Physics

Braking

• Front tire Weight transfers forward Tire deforms, contact

patch gets bigger Contact patch moves

backward

• Rear tire Smaller contact patch from

weight transfer Contact patch moves

backward faster then front tire

Y

X


Cornering Physics

Accelerating

• Front tire Weight transfers rear Contact patch smaller Contact patch moves

forward

• Rear tire Bigger contact patch from

weight transfer Contact patch moves

Forward slower then front tire

Y

X


Cornering Physics

Cornering

• Both tires Tire deforms Deflects opposite intended

path of wheel Contact patch moves

toward intended corner

Y

X


Cornering Physics

Braking and Cornering

• Combined force of braking and Cornering Maximum available is

determined by force of braking and side force of cornering

Intended path is the mean between the two forces

Front tire uses more braking force due to weight transfer

Y

X


Cornering Physics

Acceleration and Cornering

• Combined force of acceleration and cornering Maximum available is

determined by force of acceleration and side force of cornering

Intended path is the mean between the two forces

Rear tire uses more accelerating force due to weight transfer creating bigger contact patch

Y

X


Review

Key Points:

• Traction Coefficient of friction between tires contact patch and

ground Ground surface has constant changing co-efficient of

friction depending on what type of surface Contact patch can be smaller due to weight transfer,

design of tire, tire deformity Motorcycle operator must manage these forces within the

limitations of the friction circle


NEGOGIATING A CORNER

Many types of corners

• 1/3 theory

• Out-in-Out

• Vision



1/3

• Envision the lane separated into 1/3 Outside Middle Inside

• Able to legally use entire width of lane

• Hazard avoidance

• Entry point selection



Physical movement of a motorcycle cornering



Corner Basics

• Entry Beginning of corner

• Apex Cornering line

closest to inside of curve

• Exit Last part of corner



Be at the speed you want to be at to travel around the curve

Out-in-Out Start on 1/3 portion of

lane which is on the outside of the curve

• Turn to middle of curve for your apex

• Exit on outside 1/3



Vision is a fluid, seamless process moving from one step to the next

• Keep head and eyes up, as level as possible

• Approaching curve Look for entry point Look through entry point to apex

• Entry Point Look through apex Look to exit point and beyond

• Apex Look to exit Look beyond through exit to as far down roadway as

possible


REVIEW

Key Points:

• 1/3; offers hazard avoidance, entry point selection

• Have speed at what you want to travel around curve

• Out-in-Out

• Vision Fluid motion Eyes and brain constantly moving ahead Body, motorcycle will follow


REFERENCES

Motorcycle Design and Technology• Motorbooks Int’l; Gaetano Cocco, 2004

How to ride a Motorcycle• Motorbooks Int’l; Pat Hahn, 2005

Sport Riding Techniques• David Bull publishing; Nick Entsch, 2003

Proficient Motorcycling• Publisher Unk; David Hough, 2000

Green Knights M/C Club, Hanscom Chapter• http://greenknights5.com/; Gil Besana, President

Get the best from your bike, don’t let the bike get the best from you

Cornering 101

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