Performance Bikes — March 2018

MANCEBIKES.CO.UK 45

phase and full-gas phase.
“The mid-corner phase, when the rider is about
to release the front brake and hasn’t yet touched
the throttle, is key. It’s only a few metres of track but
the moment when most of the turning is done. The
bike is still rolling, with good momentum
and lean, so if this phase is precise and
well controlled, the rider can get a
good exit. The aim is to reduce the
time between releasing the brake
and the first touch of the gas. Of
course, some riders are on the
gas with the front brake still
on – they are the kings!”
Even Öhlins admit their
suspension has little effect
in the mid-corner phase,
because the rear shock is
60° from the vertical, so it’s
almost useless. Swingarm flex
and tyre deflection do most of the work.
“Then, if everything is right, the
rider uses constant throttle for a few
metres to start the rear tyre spinning,
which takes him into the next phase:

pickupthebikeandusefullthrottle.Weneedtomake

compromiseswithchassisstiffnesstomakethisphase

sweet,controllableandeasytohandle.Butgettingthe

drivespinrightwhentherearissteppingoutisn’teasy

becauseit’sanon-steadystateofloadings.”

Swingarm design is hugely important to give the

rightamountoffeelwiththetyrespinning.It’sthe

same as corner entry: too little flex and the bike will be

toosnappywhenthetyreslides;toomuchflexandthe

bike will wobble and lose grip.

Tractionunderhighthrottleloadscanbeincreased

by adjusting the relative positions of the swingarm

pivot, gearbox sprocket and centre of mass – to create

the so-called anti-squat effect. If the designer gets his

anti-squat sums correct, the rear shock extends during

hardacceleration,improvingbothreargripandfront

grip,whichiscrucialtokeepthebiketurning.

Chassis ergonomics

To go fast the rider must be comfortable, so ergonomics

is another important consideration for engineers.

“Youwantthebikeassmallandasnarrowas

possible,” says Baumgaertel. “But the rider needs to be

comfortableandrelaxedtomakeconsistentlaptimes.

Like everything else, you make compromises. You’ll be

happyifaridingpositionloses1.5mphontopspeedbut

gains0.25secondsthroughtherestofthelap.”

Riders have many different ergonomic preferences.

Some prefer rigid footpeg hangers, others like some

flex in them to damp out some of their inputs. Seat

height is important and so is seat material. Some riders

like a grippy seat, others like to slide around. Then

there’s handlebar angles, fuel tank shape, and so on.

Rider feel

Baumgaertel started out in car racing but prefers bikes,

largely because rider

feelingvariessomuchfrom

one racer to another.

“Car racing is the complete

opposite–it’salldata,more

orless,”hesays.“Ienjoy

bikesmorebecausethis

‘black hole’ that the rider calls

feeling is super-interesting. You read

the rider’s eyes to know if the bike is

working or not; the look he gives you is

moreimportantthanwhatyougetfromthe

datalogger. And we have to remember that

when a car racer gets into trouble he goes into

thegravelandthemechanicscleanthecar...but

whenabikeracergetsintotroublehefeelspain.”

Swingarm design is

crucial when it comes

toarider’sfeelforwhat

thereartyreisdoing

Baumgaertel proudly

holds aloft one of his

Moto2 chassis

LUKASZ SWIDEREK

BUENOS DIAS

Jack Miller on the Marc

VDS MotoGP bike. Premier

class machines are a

similar size and weight

to Moto2 bikes

MARC VDS

Chassis ergonomics

Each individual racer will have

varying preferences when it comes

to flex at contact points such as

footpeg hangers.

GP TECH / CHASSIS DESIGN