Cornering 101

1. Cornering 101

2. FOR OFFICIAL USE ONLYNote: This Slide is Mandatory • 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 Note: Do Not Remove “For Official Use Only” From Any Slide

3. OVERVIEW • Forces acting on a motorcycle in a corner • Suspension / Chassis dynamics • Basic cornering physics • Negotiating corner

4. 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

5. 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

6. Forces Combined CG Rider / Motorcycle Centrifugal Rider / Motorcycle equilibrium point Earth Gravity

7. 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

8. 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

9. Chassis Dynamic • Wheelbase • Effect of wheelbase determines diameter of the turning radius a motorcycle may have • Shorter allows for smaller turning radius

10. 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

11. Chassis Dynamic Rake, Trail, Wheelbase Steep, small, short Gradual, large, long Agile Less Agile

12. 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

13. Examples Extension Compression

14. 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

15. 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

16. 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

17. Cornering Physics • Cornering • Both tires • Tire deforms • Deflects opposite intended path of wheel • Contact patch moves toward intended corner Y X

18. 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

19. 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

20. 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

21. NEGOGIATING A CORNER • Many types of corners • 1/3 theory • Out-in-Out • Vision

22. NEGOGIATING A CORNER • 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

23. NEGOGIATING A CORNER Physical movement of a motorcycle cornering

24. NEGOGIATING A CORNER • Corner Basics • Entry • Beginning of corner • Apex • Cornering line closest to inside of curve • Exit • Last part of corner

25. NEGOGIATING A 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

26. NEGOGIATING A CORNER • 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

27. 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

28. 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