Strike up the band: The addition of white highlights, including the shock spring, brightens up the KTM’s looks considerably.
(1) Origination. Although new to motocross, the 4CS
forks have appeared on KTM’s 2014 XC offroad bikes and
select Husabergs since 2012. However, the offroad version
of the forks is shorter and softer than the fork on the
Factory Edition III. To turn the 4CS into a motocross fork,
WP lengthened it to match the old bladder fork, re-valved
it, put in a more aggressive bottoming cone, resprung it
and redesigned the pistons.
( 2) Chambers. The 4CS shares very little in
overall design with most other closed-cartridge forks. First,
the fork springs are on the top of the damping system.
Second, the oil height isn’t measured in cubic centimeters
of oil, but instead by fork oil height (on a compressed fork
with the spring out). Third, all of the damping is in the
lower fork-leg cartridge, where the piston on the end of
the 8mm cartridge rod plunges through a sealed volume
of oil, displacing it out of the inner cartridge into an outer
cartridge, and where it is bled off into a spring-loaded
cartridge that compensates for the rod’s volume. Got
all of that?
( 3) Damping. The compression adjuster is on the
right fork cap, while the rebound clicker is on the left
cap. That may lead you to believe that one fork handles
compression and the other rebound, but, in fact, both fork
legs have compression- and rebound-damping capabilities.
Where the right and left fork legs differ is that the check
valve on the end of the cartridge rod is reversed in each
respective leg. That means that the right-side-up check
valve can close off free bleed during the compression
stroke in the right fork leg, while the upside-down check
valve in the left leg shuts off bleed during the rebound
stroke. Amazingly simple. The left and right leg of the
4CS fork are identical, save for the flip-flop, dual-duty,
compression/rebound check valve.
( 4) Speed sensitive. The old-style KTM bladder fork
had largely position-sensitive damping, which means that
the damping was controlled by where the fork leg was in
its stroke. The 4CS fork is largely speed sensitive (where
the speed that the fork travels determines how much
resistance the shim stack generates). The rebound
damping focuses on low- to mid-speed damping, while the
compression damping is more mid and up. Changing the
rebound clicker does not affect the compression damping
as it does on most fork designs.
( 5) Tolerance. Unlike the WP bladder forks, the
sensitivity of the clickers is magnified on the 4CS forks by
a factor of 4:1, which means that what it took four clicks
to achieve on the bladder fork can be achieved with one
click on the 4CS forks. Because the damping capabilities
are so much greater, KTM installed 0.48 Nm springs in
the Factory Edition III instead of the 0.50 Nm springs
found on the
2014 KTM 450SXF. As an added plus, the 4CS fork is
6 ounces lighter than the previous WP bladder fork.
Q: WHAT DID KTM DO TO THE REAR
SUSPENSION ON THE FACTORY EDITION III?
A: The rising rate has been changed via an all-new
bell crank and 2.5mm-longer pull rod. The goal was to
stiffen the initial part of the shock stroke to lessen
wallowing and hold the rear higher in its travel. The
rising-rate curve is stiffer initially, and then flattens out to
provide a less progressive curve at the end of the stroke.
2014 KTM 450SXF