Headquarters Air Mobility Command
Cornering 101
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FOR OFFICIAL USE ONLY
Note: This Slide is Mandatory
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The information presented here is for informational
use only
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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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OVERVIEW
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Forces acting on a motorcycle in a corner
Suspension / Chassis dynamics
Basic cornering physics
Negotiating corner
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Forces
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General Theory
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Motorcycle turns via deflection of front wheel/tire
 Makes motorcycle lean opposite path of wheel/tire
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 Motorcycle actually moves opposite intended path first
Tires/corner effective radius becomes smaller
 Styrofoam coffee cup on its side
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 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
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Forces
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Motorcycle and rider are independent of each other
with same forces
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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
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Forces
Combined CG
Rider /
Motorcycle
Centrifugal
Rider / Motorcycle
equilibrium point
Earth Gravity
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Chassis Dynamic
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Chassis
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Rake, is the angle formed by:
 Line drawn from center of steering head through tire to
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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
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stability)
As suspension compresses on fork-equipped
motorcycle, effective rake and trail get smaller, thus
steering quickens stability decreases
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Chassis Dynamic
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Chassis:
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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
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Chassis Dynamic
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Wheelbase
 Effect of wheelbase determines diameter of the turning
radius a motorcycle may have
 Shorter allows for smaller turning radius
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Chassis Dynamic
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Single track vehicle is unstable
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Gyroscopic force created by turning wheel/tires creates
stability
 Greater the speed, greater the stability
 Larger the diameter, greater the stability
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All chassis and suspension dynamics affect amount of
force needed to move stability created by turning
wheel/tire combination
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Chassis Dynamic
Rake, Trail, Wheelbase
Steep, small, short
Gradual, large, long
Agile
Less Agile
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Review
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Key points:
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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
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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
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Examples
Extension
Compression
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Cornering Physics
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Tires
• Ffriction= f x C
Y
 f is theoretical coefficient
of friction whose max
value is 1
 C is vertical load bearing
on the wheel
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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
X
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Cornering Physics
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Braking
• Front tire
Y
 Weight transfers forward
 Tire deforms, contact
patch gets bigger
 Contact patch moves
backward
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Rear tire
X
 Smaller contact patch from
weight transfer
 Contact patch moves
backward faster then front
tire
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Cornering Physics
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Accelerating
• Front tire
Y
 Weight transfers rear
 Contact patch smaller
 Contact patch moves
forward
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Rear tire
 Bigger contact patch from
X
weight transfer
 Contact patch moves
Forward slower then front
tire
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Cornering Physics
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Cornering
• Both tires
Y
 Tire deforms
 Deflects opposite intended
path of wheel
 Contact patch moves
toward intended corner
X
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Cornering Physics
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Braking and Cornering
• Combined force of braking
and Cornering
Y
 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
X
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Cornering Physics
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Acceleration and Cornering
• Combined force of
acceleration and cornering
Y
 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
X
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Review
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Key Points:
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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
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NEGOGIATING A CORNER
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Many types of corners
• 1/3 theory
• Out-in-Out
• Vision
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NEGOGIATING A CORNER
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1/3
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Envision the lane
separated into 1/3
 Outside
 Middle
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 Inside
Able to legally use entire
width of lane
Hazard avoidance
Entry point selection
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NEGOGIATING A CORNER
Physical movement of a motorcycle cornering
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NEGOGIATING A CORNER
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Corner Basics
• Entry
 Beginning of corner
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Apex
 Cornering line
closest to inside of
curve
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Exit
 Last part of corner
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NEGOGIATING A CORNER
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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
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NEGOGIATING A CORNER
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Vision is a fluid, seamless process moving from one
step to the next
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Keep head and eyes up, as level as possible
Approaching curve
 Look for entry point
 Look through entry point to apex
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Entry Point
 Look through apex
 Look to exit point and beyond
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Apex
 Look to exit
 Look beyond through exit to as far down roadway as
possible
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REVIEW
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Key Points:
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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
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REFERENCES
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Motorcycle Design and Technology
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Motorbooks Int’l; Gaetano Cocco, 2004
How to ride a Motorcycle
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Motorbooks Int’l; Pat Hahn, 2005
Sport Riding Techniques
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David Bull publishing; Nick Entsch, 2003
Proficient Motorcycling
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Publisher Unk; David Hough, 2000
Green Knights M/C Club, Hanscom Chapter
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http://greenknights5.com/; Gil Besana, President
Get the best from your bike, don’t let the bike get the best
from you
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