running. Plus the bike has a very,
very, very long swingarm, with ex-
tra internal plates to add stiffness.
This swingarm is so long that it
has less effect on anti-squat. If the
anti-squat doesn’t change under
power, then that’s one less thing
the rider can control with the gas.
The bike looks very front-loaded.
They put all the weight they could
up front, so they must’ve had
more power than they wanted.
Öhlins: “It’s a long swing-
arm, but a lever ratio is a lever
ratio, even if the arm is that long.
So long as the spring rate working
the axle is correct and you’ve got
the right amount of chain force
and anti-squat [which stops the
shock from compressing too much
under power] then it doesn’t mat-
ter if the swingarm is long. In fact,
if you have a long swingarm the
swingarm angle doesn’t change
much, so the chain force stays
more or less the same, so the rid-
er has more confi dence about how
the bike will behave in certain sce-
narios. Some chain force is a good
thing: When you are at full lean,
starting to accelerate and the bike
is compressed, you want these
forces to pull the rear wheel into
the chassis; you don’t want the
forces pushing the wheel out.”` 2013 Yamaha YZR-M1
The YZR-M1 was at its peak in
the fi nal years of Bridgestone tires,
carefully and logically developed
since Valentino Rossi fi rst climbed
on the bike in 2004. By this time,
the factory had a very good handle
on the science of chassis stiffness
and probably would’ve won the2013 title, but for the genius of
rookie Marc Marquez.Kalex: “Now the beam sec-
tions are machined from solid bil-
let and the front engine hangers
are even longer for more lateral
fl ex; this is probably for more lon-
gitudinal stiffness, but less lateral
stiffness in the corners, with a wall
thickness of maybe less than 1mm,
like a Coke can! The hole in the
beam isn’t just for a front stand,
it’s a section connecting the left
and right beams, so it completes a
triangle for extra longitudinal stiff-
ness for better braking stability.
Swingarms are now upside down;
I think because the force from the
tire comes from below, so this is
where you get the stresses and
this way you better can force the
stresses into the shock.”Öhlins: “Look at the fork
bottoms. By this time they were
created via FEM [fi nite element
method, for structural analysis,
etc.]. We make a model, then ap-
ply loads and brake torque, so you
can see where the stress goes. This
allows us to move material around
and minimize weight. It looks like
the CNC machine has gone wild,
but the stress is more evenly dis-
tributed and the fork bottoms are
lighter than the magnesium ones
we used to use, which also had a
shorter lifespan. The frame looks
beefy but there’s no chunky box
section inside. Beams are much
narrower now; in general much
less stiff than the 1989 NSR. And
the swingarm is so light you could
probably bend it with your hands.”` 2018 Suzuki GSX-RR
Suzuki raced the GSV-R V4
from 2002 to 2011, then with-
drew for three years while compa-
ny engineers created the GSX-RR
Inline Four for 2015. The bike is
the best-handling on the current
MotoGP grid, able to race with the
faster Ducatis and Hondas, de-
spite a horsepower handicap.Kalex: “This is a beautiful
thing—the loveliest! They have de-
tachable engine hangers, which
is smart; the fact that this is an
adjustable part tells you that this
is a key area, where you need to
work. Beneath the black covers on
the beam sections they probably
have different carbon-fi ber sections
to get the right twist points.They
have four engine mounts, which is
also good, because you have more
chance to adjust things. I like In-
line Four engines, because I think
it gives you more freedom. With a
V4 you fi ght with exhaust position
and there’s only one place you can
put the fuel. The V4 is only for pow-
er, but MotoGP bikes have so much
horsepower they only use full pow-
er for a few percent of each lap.”Öhlins: “Suzuki (engineers)
have done their homework. I ap-
plaud them because this bike is
very, very well thought out. You
watch how Alex Rins goes into a
corner too hot, runs wide, then
he just pulls it back online. The
others can’t do that, except [Marc]
Marquez with his acrobatic ma-
neuvers. All the factories use our
carbon-fi ber forks, which are very
stiff but give lateral fl ex in the cor-
ners. We can adjust the stiffness
of our forks with the direction we
lay the fi bers, how we wind the fi -
bers and so on. But at the moment
everyone uses the same stiffness
forks. The manufacturers also
have different triple clamps and
different steering-head bearings
set-ups to adjust twist to improve
corner entry.”(Above) The 2013 Yamaha YZR-M1 Inline Four was at its best with Bridgestone spec tires, when Yamaha en-
gineers had a handle on the science of chassis stiffness. But Honda’s rookie genius Marc Marquez won the
World Championship! (Below) The 2018 Suzuki GSX-RR led to the 2019 version being the best-handling Moto-
GP bike on the grid, allowing Alex Rins to run at the front despite the Inline Four not making the most power.
RWRoadracing World, August 2019—25