English Version

Union Jack Flag_A_SS-1Eric Offenstad: Geco, Current technical tendenciest:
GECO MOTORCYCLES :
« – TRACTION: Swing arms are getting longer and longer in order to keep a more constant angle, less ANTI-SQUAT variations and less « bump accelerations ». This fact is inducing frontwards weight-distribution.
– MANEUVERABILITY: Due to constant OFFSET, relevant amount of TRAIL entering corners is obtained by a change of CASTER angle proportional to a change of attitude of the chassis. More change of attitude for maneuverability needing short wheel-bases and hight center of gravity.
– BRAKING: As soon as rear wheel starts lifting from the ground, the rider has to reduce the brake pressure: The weight distribution not standing up to the « harsh tests of the physics ».

Performance analysis
– Brembo is providing MotoGP braking distances on every circuit. On the Mugello for instance MotoGP braking distance is 315 meters where F1 are not needing 100 meters.
– Performance evolutions: While F1 braking distance have been cut by three in 30 years thanks to aerodynamics and tires chemical grip improvement, motoGP braking distance have barely changed since the maximum chemical grip allowed before « turning over head first » was already reached in 1979.
– Michelin development engineers are aware of the fact that MotoGP bikes can’t stand up to current G.P.Tires adhesion and that their is a great potential improvement in motor-cycle weight-distribution and mechanical grip in order to match current chemical grip of the tires.

Functional analysis
– Step by step development of current bikes is relevant for choosing the best « OFFSET » compromise (For instance between maneuverability entering corner and stability outing corners).
FUNCTIONAL SPECIFICATION methodology we are using is by-passing compromises, it’s choosing the best offset for entering corners as well as the best offset outing corners.
– For front suspensions of all kind it’s featuring PROGRESSIVE offsets and specified trail.
– « CONSTANT VELOCITY » has been used on car transmissions for half a century, even it it’s only a small part of the grip, as with a car lateral grip is essential, where a bike being 100% longitudinal: constant velocity or bump accelerations (IUWA) are essential for traction and entering corners « with the brakes on ».
– Constant velocity braking has been the subject of the year for 24 student of the University of Technology of Montpellier. The recurrent « Loosing the front » issue can now be corrected with it’s proper algebraic formula.
– On the rear, constant velocity (tested on a 500cc G.P. Honda V2) is cutting down tire wear by 40%.

Studies & development
All known front suspensions have been designed the « step by step » way, none has yet been designed by the rational « FUNCTIONAL SPECIFICATION » and therefore have always been irrelevant in providing constant velocity as well as a correct TRAIL for every chassis attitude. Elf or Yamaha 1000GTS are coming short in providing relevant caster kinetics. Current Britten/Fior/BMW Duo-Lever can’t provide relevant caster variation as well as constant velocity.
JBB/TESY/VYRUS « steering-hubs » created in 1925 by George WALLIS has had more time to develop it’s simple kinetics and have reached a descent compromise between « constant velocity » and descent trail variation.
GECO SPECIFICS:
– Studies with Montpellier University of technology has led to a « constant velocity » telescopic fork.
– Trailing link front suspension designed by functional specification in order to get 100% constant velocity for maximum grip entering corners with the brakes on, as well as a relevant amount off trail for every attitude o the chassis for maximum maneuverability
– Three shock absorbers similar to the racing car system, providing a different flexibility for braking, accelerating and constant speed cornering and therefore avoiding the current compromise having to choose between braking distance and traction.
Because functional specification allows exiting current compromises the GECO cant optimize traction, braking, maneuverability and stability at the same time.

Technical choices.
– Trailing link front suspension system has been chosen for its very good shock absorption kinetics, its very favorable unsprung weight, and its ability to provide constant flexibility.
– Frame is a classic Ducati type tubular frame on wich we are using 6082 aluminum tubes for optimum weight.
– After having designed two different parallelogram rear suspension we were unhappy about it’s unsprung weight standings and decided to switch back to a traditional swing arm. Our cross-over shaft allowing to choose the best transmission for constant velocity issues and inboard rear brake for minimum rear unsprung weight.
– Brakes are offered by BERINGER and MICHELIN is supporting us for tires, tests and technical help. »

2 réflexions au sujet de « English Version »

  1. Dear Sir,
    Over the years I have become something of an expert in linkage front suspension systems having to evaluate designs for European motorcycle manufacturers and being asked by one of the big Japanese manufacturers to design one.
    I can see improvements to your design of trailing link, but was wondering where you are placed in regards to racing program, production of, and financing to complete your trailing link development?

    • Dear Mr. RAE,
      Our trailing link design is only the visible part of the iceberg. The main issue of the GECO being to dump step by step design and replace it by design born from « functional specifications ». In clear, designing a motorcycle able to bring what the rider needs to go faster: that is more traction, shorter braking distance, more grip entering corners, steering geometries providing better feed-back.
      But, as you are pointing out: we are not yet considering racing program or production as we are concentrating in developing the rest of the bike (The trailing link itself being already providing better « feed-back » to the rider than a telescopic fork.)
      Best regards
      Eric Offenstadt.

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