Introducing The Expert: Greg McDonald
Marc Márquez is a lean angle magician on a MotoGP bike. The Repsol Honda rider regularly uses 60° or more to wrangle his RC213V through corners. The rest of us – and his rivals – stand in awe, and wonder how he manages to get away with it.
Yet he has also said he would rather not use so much lean angle. There are easier ways around the corners, but with the 2019 Honda RC213V, using a lot of lean angle is the only way Márquez can maintain his competitiveness.
Why does he need so much lean angle? Keen to find an explanation for this I got in touch with Australian chassis expert Greg McDonald. McDonald worked as a GP and Superbike ‘insider’ for many years, but was previously reluctant to talk about the work he did for a string of factory teams, for commercial reasons.
These included Martin Adam’s Smokin’ Joes (American Honda) team in the USA, several projects with Team Roberts – including a little known 125GP machine - and a collaboration with the late Warren Willing to develop the Suzuki 500 on which Kenny Roberts Junior won the World 500 Championship in 2000.
These teams all bought Computrack machines, designed and built by Greg McDonald, to help make their bikes competitive.
More recently he collaborated with Willing on a 2013 test project with Ducati – prior to the arrival of Luigi Dall’Igna.
A quest for precision
McDonald is an ex-racer (dirt-track and road-racing) who ran a successful crankshaft re-building business for many years before branching out into straightening the frames of crash damaged motorcycles.
Frustrated by the lack of accurate equipment he decided to develop his own three-dimensional co-ordinate measuring machine in the 1980s. This was patented under the name ‘Computrack’ and won him The Australian (newspaper) Innovator of the Year Award in 1987.
Put simply, McDonald applied the same attention to detail from his crankshaft re-building days to chassis measurement. To him, a one millimetre tolerance is not to be countenanced; McDonald works to one hundredth of a millimetre.
It was not long before a few racers started showing up to have their crashed machines measured and straightened. From there McDonald started exploring the subject of chassis geometry with the aim of getting the best settings possible for good handling.
Hideo ‘Pops’ Yoshimura was his first overseas customer, the legendary engine tuner buying a Computrack as he saw it as “the way of the future.”
McDonald expanded his network to the USA and Europe and built up a huge database of chassis geometry from working on private customer’s bikes in addition to the factory-backed teams and OEM product development and quality audit.
Ask the expert
It is doubtful there is anyone else in the world with the breadth of chassis experience across a vast range of motorcycles.
Now here is his response to the question: why does Marc Marquez have to use such extreme bank angles with the Repsol Honda?
On Friday at the Sachsenring, Marc Márquez told reporters he was having to use a lot of lean angle in order to make good lap times with the Repsol Honda. “If you check a little bit this year, we are using a lot of banking, too much, and why we are using banking is because the package is not turning. Then I use all this banking, not because it’s my riding style, not because I like it, but because I need to.”
Marquez’s comment was backed up by Cal Crutchlow: “Unfortunately, we need to lean this bike more to turn, but every time I lean the bike more, I slide off the bike, I crash," the LCR Honda rider said. "And that's just not my style."
This takes me back to the Honda RC30 days of chassis set-up with Aussie racer Shawn Giles’ bike that Tony Hatton and I collaborated on, a Moriwaki-powered RC30 he raced in Australia, and the Honda RC45’s I did with the American Honda, Commonwealth Racing bikes in the AMA Championships. The issue regarding what parameters are needed for the lean angle necessary for the racing line on a given radius corner is still not well known.
Checking the numbers
Using GMD Computrack and using a holistic approach – measuring all the numbers of a motorcycle’s geometry – I discovered there were eight parameters that needed to be correctly set to obtain the optimum grip to reduce the lean angle necessary for a given radius of turn.
The process is to change all the necessary geometry parameters in one step to get the chassis close to optimal, which gives the feeling of grip and very early warning to the rider. Then fine-tune from there (which is what Tony Hatton did with Giles’ RC30).
If a team does this one step at a time, they never seem to get it nailed. It is vital to look at the chassis geometry in totality and adjust everything that is necessary to get the complete package.
We learned a long time ago that when less trail is used, a rider needs to use more lean angle for a given rate of turn.
In many cases the pursuit of very light steering feeling does not mean better turning: but it does mean more lean angle is necessary.
The MotoGP teams work/develop in a very closed environment, with a very limited experience on only a few different bikes.
Seeking grip through geometry
Years ago, the Computrack 3D measuring machines were purchased by 12 OEM and many factory-backed GP and national race teams around the world. They were bought because they had proved their worth, with the data from each successful project being fed back into the database of bike set-up data, helping to refine the model.
The progressive staff wanted to know what the chassis tolerances were, and what the defined overriding parameters were from that database. The answer was simple, replace the words ‘weight’ and ‘flex’ with the word ‘grip’, and then the chassis geometry set-up parameters that needed adjusting became clear.
Superior motorcycle handling is about controlled grip, or traction. Much is written about weight bias and chassis flex etc. but if a motorcycle’s suspension and geometry is not working in harmony to capture the opposing forces and convert them to grip, then chassis flex etc. will not give the desired result.
Stiction vs flex
We never hear how the impact of the chassis flexing affects stiction (sliding friction – the resistance of the fork stanchion from sliding in the outer tubes) - the most common problem we find. Riders often misinterpret excess stiction as tyre grip, but even small binding in suspension movement takes away the feel of early warning from the front tyre. Even a small twisting of the forks from a crash, or in practice sessions or the race (often due to less than optimal fork clamps) can cause stiction.
With the very fine tolerances in the bushings of the beautifully engineered modern forks, smooth motion is vital. In addition to optimal chassis geometry, our focus is on the first one to two millimetres of suspension motion in any change of direction with low inertia, such as the release of the front brake and the initial throttle opening. Smooth, non-binding fork action at this moment is vital for maintaining front tyre edge grip and providing critical early-warning feedback to the rider.
Without that, there is a vastly increased risk of front-tyre ‘tuck under’ – or ‘closing the front’ as the Europeans put it.
It is hard to see how increasing chassis flex with the attendant risk of suspension binding, which alters the feedback to the rider, always increases grip.
It has been stated in many forums that motorcycle suspension does not work when the motorcycle is at extreme lean angles. This certainly is a challenge, and it is at these extreme lean angles where it is critical to have the suspension working smoothly, for the reasons already outlined.
Stiction and ‘chatter’ (sometimes called ‘patter’) are the result of the delayed release of stored energy, mostly caused by suspension ‘binding’.
The focus of the GMD Computrack user network is to identify these real chassis problems, optimise the parameters and make them work for the rider.
The aim is to identify and rectify. Or put another way, optimise without compromise.
I will go on record as saying that from our findings, so much that is written on this topic today is "running wide and off-line".
There is a huge difference between the data obtained around the world over 30 plus years by those using Computrack to measure bikes and set their geometry numbers, as compared to those who obtain expertise from a very small sample.
Leaning versus turning
The lean/turn issue we discovered in 1988. We learned that optimising the entire chassis geometry was the way forward. The optimal steering rake must be matched with the correct amount of trail, swingarm pivot height and the other five parameters, working to very fine tolerances.
That's why I say that Marc Márquez is having to use so much lean angle. The Repsol Honda is using geometry that gives very light steering, but the excess lean angle is a side-effect of that. To change the geometry would make the steering seem heaver, but not change the rate of turn, it’s a matter of the riders feeling preference, and would need a few track sessions to assess. This is exactly the sort of problem the GMD Computrack is designed to solve.
I hope to explain a bit more about the whole process in a series of articles here, to help people understand how the geometry of motorcycles affects how they behave on track.
People who strive for excellence is chassis technology may contact Greg McDonald via
GMDCOMPUTRACK.com. The purpose of these articles is to share knowledge and reach out to the next generation of riders and teams, to pass on what I know to all interested, intelligent people. Motomatters.com is the perfect forum for that.
People who strive for excellence in chassis technology can contact Greg McDonald via GMDCOMPUTRACK.com. The purpose of these articles is to share knowledge and reach out to the next generation of riders and teams, to pass on what I know to all interested, intelligent people. Motomatters.com is the perfect forum for that.
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