WHAT YOU NEED TO KNOW ABOUT WP’S ACS
(1) Internally, the ACS air shock is the same as that on
the spring shock, as damping is damping no matter what
medium is being used as a spring.
( 2) The shock has two air chambers. In this, it is not
unlike the second-generation Fox Airshox of 40 years ago.
( 3) Although a version of the AER air forks will be on
America-bound bikes in 2017, the ACS air shock is all
about new technology and is not about production. It is
unlikely that this shock will see production soon.
( 4) WP refused to let us see the secret shock
component that was hidden inside the airbox, but it
doesn’t take a genius to figure out what it is. What is it?
A regulator. Similar to Georges Jobe’s air shock and even
to Yamaha’s speedo and tach forks, which had canisters
with two different air pressures separated by a piston to
keep pressure gains under control, the WP ACS shock’s
regulator relieves the built-up air pressure by enlarging
the air pocket as the air expands under heat. We aren’t
surprised that there is nothing earth-shattering hidden in
the airbox. It’s all been done before. We assume that the
secrecy is about exactly how the pressure is regulated
to keep Andrew Short’s shock set at the same air
pressure he started with.
( 5) WP says that the air shock does not weigh any less
than the coil spring shock it replaces, probably because
of the regulator in the airbox.
WHAT YOU NEED TO KNOW ABOUT ANDREW
SHORT’S BTO KTM 450SXF
(1) Andrew gets the exact same engine as Ryan
Dungey from KTM’s Factory Services engine shop. Given
that we tested Ryan Dungey’s National Championship
KTM 450SXF on the same track a few months earlier,
we can assure you that this is a powerful engine that
seems easy to ride but will surprise you if you wick it on
instead of rolling it on. It didn’t matter where you were
in the powerband; it had the perfect power.
( 2) The BTO team runs a Pirelli Mid-Soft 32 on the front
and a 110/19 Mid-Hard rear on Excel rims laced to Talon
carbon fiber hubs.
( 3) For pucker power, Andrew goes one-up on the
typical KTM setup with a 270mm Galfer front rotor with
Brembo’s 28mm caliper and 10mm piston in the master
cylinder. We were surprised to find a very old-school
shorty front brake lever from the 1990s on Andrew’s
bike. We haven’t seen this on a works bike in ages,
but with a 270mm works front brake, you don’t need
four fingers on the lever.
( 4) Andrew’s gearing of choice changes with each
track, but since his bike came to us straight from the
Indiana National, it had 14/52 gearing.
( 5) There was a 2.0 radiator cap and a cooling fan
from the KTM enduro bikes mounted behind the
radiator. Heat is obviously a concern.
( 6) Everyone remembers Ryan Dungey’s air shock
failure when his bike suddenly went low-rider. That was
an early version of the ACS shock. The problem was
related to excessive vibration of the seal. Andrew Short
did not have a single issue in 2015.