Project - Designing the perfect motorcycle.
To create the perfect motorcycle optimum geometry is paramount.
Raerdesign devised the missing theory regarding bike geometry circa 1992. Until then, it had been considered a dark art on how to make bikes handle precisely yet remain stable. Both dynamic considerations are possible once this theory is acted upon. The historical background: In the 1980s hub-center steered motorcycles with smaller front wheels and ultra steep steering-head angles were incredibly stable yet quicker steering compared to telescopic fork equipped bikes, where these motorcycles conflicted with the perceived wisdom of the era.
With a spinning wheel gyroscopic precession operates creating a force of turn or tilt at 90 degrees to the axis it rotates upon, wherewith a secondary axis protrudes out from the front wheel axle perpendicular to the steering axis to govern the relationship between front wheel size, steering-head angle and wheelbase length; as seen in the diagram. For optimum performance, it is best to have the secondary axis intersect the road surface just in front of the rear tire contact patch so to be underneath it at a minimal distance, because when this axis is excessively distanced from the contact patch this results in heavy feeling steering plus slower response times from rider input.
When this theory is fully implemented, it determines a smaller front wheel should be utilized to steepen the steering-head angle thereby further lightening and quickening the steering yet retaining excellent stability. Further, with the front wheel smaller than the rear this has the longitudinal dynamic plane sloping forward to put dynamic influence onto the front yet a central positioned center of gravity can be retained for optimum handling. An imperative requirement given that a steeper steering-head makes it easier for riders to loose the front wheel during a slide, but there is a secondary method of overcoming such a risky syndrome (not detailed here).
What the above demonstrates is with most motorcycles the optimum steering-head angle is around 15 degrees combined with the optimum wheel travel path is 11 degrees of rearward inclination (devised from the automotive industry to provide best compromise between braking dive yet retain suspension action). Four degrees difference between these values is not an issue, for it decreases trail during compression to the benefit of cornering prowess.
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A low center of gravity (CoG) benefits rider control road-holding and handling, yet a high CoG improves cornering potential. When cornering, a high CoG requires reduced motorcycle lean angles for a set trajectory and velocity, as demonstrated in the diagram. A centralized CoG is best for overall handling road-holding and control but to increase cornering potential a forward positioned CoG functions best. However, this increases inertia associated with front wheel slides increasing the risk of crashing. As said above, with the bike's dynamic plane sloping forward such can alleviate this conflict of interests by allowing for a centralized CoG yet retaining good cornering potential. Further, with braking a high CoG benefits front wheel braking by excessively loading the front yet a low centralized or rearward CoG benefits joint front/rear braking. With reduced dive (provided by an alternative front suspension system) optimum braking of both wheels provides the safest shortest stopping distances. Perceived contradictions in chassis design criteria can be offset with a combination of advanced technology relating to tire profiles, chassis structure, layout and rider positioning to benefit braking handling road-holding control safety and cornering.
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Mass centralization refers to the clustering of components around the center of gravity, and is found to benefit rider control, handling and safety therefore it is a principle that should be adhered to when designing any bike.
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Front suspension design needs to alter because telescopic forks cannot function adequately at high speed at 11 and 15 degrees rearward inclination. To retain the same level of feedback telescopic forks provide, there can only be one component motioning between the front wheel and the handlebar fixture, which gives the choice between leading link and trailing link front suspension. Given leading link is dangerous and has the wrong front wheel travel path only trailing link can be used to replace telescopic forks (which has the benefit of an ideal wheel travel path).
A simple linkage system has been devised for the rear suspension to prevent 'highside' crashes, and swinging arms should be braced underneath only, as Raerdesign informed MotoGP fabricators, which is now accepted universally for racing.
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The rear air scoop on the Ducati MotoGP bike is an old design Raerdesign devised 20 years ago. An ideal version is to have the scoop forward of the swinging arm pivot point, where this will benefit high speed aerodynamics yet act as a cornering device creating drag similar in operation to dragging the rear brake when cornering, but this is a safer method of achieving this reaction. Raerdesign possesses a front version of this air scoop to make motorcycles fully aero active to achieve cornering potential similar to sports cars, yet have the capability of higher top speeds. With trailing link suspension, in conjunction with other layout changes, aerodynamics can be vastly improved.
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When braking, kinetic energy from the spinning front wheel loads the front suspension for safe braking with trailing link suspension, unlike telescopic forks where braking force has to be fed in before maximum braking force can be safely applied to prevent locking of the front wheel. A new layout devised will vastly improve rear wheel braking.
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For structural considerations, torsional and longitudinal stiffness is easily achieved yet lateral flex can be designed into this new structure of motorcycle comprising trailing link suspension to benefit braking and cornering potential, plus it is now easy to avoid the frequency range of 65 - 70 hertz where cornering chatter occurs within the chassis. Different frame materials have different properties where frame design has to be matched to the material utilized.
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The engine crankshaft should be positioned high for least resistance when changing direction for an agile motorcycle yet low for stability, where again a method (not shown) exists of alleviating these dynamic concerns.
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All other aspects of design have been considered in this project to create the perfect motorcycle!
About
With an uncle, Bill Rae, who raced MotoGP and being a grandson of Flora Gregg of the same family fame that introduced tractors into North America,devised farm implements and agricultural systems to arguably advance the continent more than any other Robert Rae was destined to excel. At 15, he invented a simple version of constant chain tension for a motocrosser. From there, Rae would have many world leading achievements to include re-engineering the operating principle of the two-stroke engine, remain the only person to resolve the design faults of the Bimota V Due engine, produce CVT transmissions operating with as few as three moving components that are not driven by friction, be successful with what were deemed impossible tasks such like rear wheeled steering on bikes, produce many different front suspension designs, and, devise directly connected suspension as the most efficient simplest arrangement ever. Praised from the best in the business and with university professors at his beck and call he has led technology...
