MotoGP Tech Talk – Swingarms

Former International Road Racer, MotoGP Engineer, Elite Trainer and Moto Journo Mark McVeigh shares his unique insight into the world of MotoGP.

Behind the scenes, MotoGP Engineers are continually refining and modifying their state of the art 2-wheeled missiles.

It’s only when you can’t hide those design revisions that the Journo tongues start wagging.

Chassis flex, for example, is in the spotlight again recently with an updated swingarm on Marc Marquez machine clearly visible from Le Mans.

Designed to close the gap on Yamaha with improved tyre edge grip, acceleration, and corner entry, Honda have reduced stiffness and thus increased the flex of the swingarm on the RCV213V.

Comparing the swingarms above its looks like HRC have simply cut a hole in the right hand side of the swingarm to increase flex, however there’s a bit more to it.

So how does this one modification improve so many aspects of the bikes performance?

Well let’s start by explaining some of this Engineering terminology.

Flexibility

Flex is the chassis ability to absorb force, bend in different directions and return to its original position.

Lateral means sideways, so lateral flex is bending in the side or the bikes vertical plane namely when the bike is cornering on extreme lean angles.

Uncontrolled frame flex whether it be lateral (Sideways), torsional (twisting) or vertical can be thought of as the bike behaving in an elastic state. It has a clear influence on the bikes handling, feeling slow and heavy due to the dynamic geometry changes taking place with trail, wheel alignment, etc.

Chassis Flex

The ideal amount of chassis flex allows an element of lateral flex to absorb the bumps whilst retaining stiffness in torsion so the wheels are in the same plane and to control braking and acceleration forces in the vertical plane.

Stiffness on the other hand is the chassis resistance to deform under loads generated from cornering, acceleration and braking.

Chassis performance comes down to the overall flex, stiffness and strength of the frame, swingarm, forks, engine mounts, triple clamps and other components working together in harmony without creating chatter.

Chassis material and its thickness, internal ribs and how they are welded together all influence stiffness and flex.

Check out the photos of effectively the same swingarms on Haydens (above) and Lavertys (Below) Aspar machines, but with two different seams.

If one of those components’ stiffness changes the overall balance and feel of the bike will change.

Complex Engineering

Motorcycles are also notoriously one of the most complex machines to Engineer. It’s very difficult to change one aspect of the bike independently without affecting other areas of the bike.

An example of this chassis component interdependence is the recent trend of underslung swingarms in MotoGP and WSB, the bracing having moved from the top to underneath the swingarm.

This design is more efficient at reducing lateral tyre contact patch movement when the swingarm twists.

Also worth mentioning is a rule of thumb in any engineering design, which is to change stiffness gradually as a component often fails at the point where there is a sudden change of stiffness.

Ducati famously forgot this rule with their GP11 carbon fibre chassis, which was basically, short and stiff sub-frames connected to a very stiff motor.

Bend Like A Tree

The chassis should bend like a tree according to Yamaha legend Engineer Masao Furusawa.

A longer chassis creates a long lever, which allows flex to be designed more gradually, accurately and effectively.

So just how do MotoGP Engineer’s work out the right amount of strength, stiffness, flex and in what plane or direction?

Well, Engineers increasingly evaluate huge amounts of data in MotoGP, which can be measured, quantified and related to the bikes performance.

However it’s difficult to quantify what the rider feels and it’s this conundrum that ensures race engineering remains a balance between an empirical art and science.

Subsequently the factories go through an incredible amount of research and development to settle on the motorcycles overall handling performance.

R&D

Computer aided engineering tools such as Finite Element Analysis are used by Engineers to test designs in the virtual space. The whole bike is modelled in 3D CAD and deflection; stress, vibration, buckling, etc can be tested and validated before making physical parts.

In the end though, racing is a head game and it really all comes down to what the rider feels.

Adapting

Relentless tyre performance gains and the ensuing extreme lean angles ensure that engineers are constantly refining the balance between stiffness and flex to increase the overall performance of the bike and more importantly give the rider that all important feel.

Riders too have to change and adapt, just look at Rossi who has modified his riding style massively to make it more modern and adapt to the new tyres.

Its now Marc Marquez turn. The Spaniard is aware that his hallmark rear end corner entry slides are costing him time and he will adapt his riding style; substituting the time consuming slides for an improved rear floating feeling on turn in courtesy of Honda’s latest flex enhanced swingarm design.

Photographs: ©2015–2015 by Scott Jones / PHOTO.GP – All Rights Reserved