WHAT IS IT? In 2016 KTM changed its rising-rate
linkage. It was a major change, as the shock spring rate
dropped from 57 N/m to 48 N/m on the 450SXF. This
was a sure sign that the leverage ratio was dramatically
different. But, when the 2016 KTM 450SXF came out,
every MXA test rider felt that the 48 N/m spring was
too stiff for the rising rate. The backyard fix was to drop
the 48 N/m spring for a softer 45 N/m spring (borrowed
from the 2016 KTM 250SXF). Pro Circuit elected to go
a different route and designed a completely new shock
linkage—bell crank and link arm—to change the rising
WHAT’S IT COST? $349.95.
www.procircuit.com or (951) 738-8050.
WHAT STANDS OUT? Here’s a list of things that
stand out with Pro Circuit’s 2016 KTM linkage system.
(1) Linkage theory. Shock linkages work by compressing the shock from the bottom while it is being
compressed from the top by the energy of the bump. By
altering the speed of the shock per millimeter of stroke,
you can increase the damping as the shock moves
upward. In theory this allows for a softer feel in the first
one-third of travel, progressively stiffer damping in the
middle third and supreme bottoming resistance in the
final one-third of the stroke. This ever-increasing speed
per millimeter is called rising rate, and it has been the
basis of all single-shock suspension systems since the
early 1980s. It is common practice for the manufacturers to devise new rising rates virtually every year, often
making the shock faster at the end of the stroke to give
it more bottoming resistance for Supercross and then,
one year later, going to a less progressive rate change
to make the suspension feel plusher. And that is exactly
what the Pro Circuit KTM linkage system does. The 2016
KTMs come equipped with an OEM linkage system that
feels harsh and stagnant, whereas the preceding 2015
model had an OEM linkage system that was lazy and
soft-feeling. Both the 2015 and 2016 shock linkages made
it difficult to reach optimal handling performance. As for
the new Pro Circuit linkage system, it utilizes some of
the mechanical advantages of both designs. In essence it
splits the difference between the 2015 and 2016 linkages.
( 2) Link arms. Don’t confuse the Pro Circuit KTM
450SXF linkage system with the more commonplace
longer linkage arms. Longer link arms do not change the
rising rate—only the starting point of the shock on the
leverage curve. Pro Circuit’s linkage system has longer
arms ( 149.2mm versus the stocker’s 148mm), but it also
has a completely different bell crank, which is the cam
that speeds the shock up as it moves through its stroke.
The Pro Circuit link system isn’t an add-on; it is different
in every aspect.
( 3) Spring rate. Since Pro Circuit’s rising-rate curve
is softer from beginning to end, it allows—actually
demands—that the rider use a stiffer shock spring. For
small and light riders, it works well with the stock 48
N/m spring, but bigger or faster riders will need a
stiffer shock spring (typically between a 49 N/m and a
51 N/m). As a test we put our preferred 45 N/m spring
on with the Pro Circuit linkage system to see what
would happen. It left big black rubber stripes under our
rear fender. That proved to us that we needed to go to a
stiffer spring. One caveat: KTM rates its shock springs in
Newton meters (N/m), while most aftermarket companies
use kilograms per millimeter (kg/mm). So, you have to
double-check that you are actually getting a stiffer shock
spring. For example, a 45 N/m spring is a 4. 6 kg/mm
( 4) Fitment. The Pro Circuit linkage fits on every
2016 KTM and Husqvarna model (and will work on the
2017 bikes). Pro Circuit did not make linkage or link
arms for the 2015 KTMs.
( 5) Suspension performance. Once you find the
proper spring rate (and for riders under 190 pounds, we
would start with the stock 48 N/m), the KTM suspension
works better over small bumps and has a smoother transition through its full stroke. It loses the stagey feel that
made the KTM rear feel as though it had three different
phases to the shock stroke. We liked the Pro Circuit link.
As an added plus, it lowered the seat height by 7mm.
WHAT’S THE SQUAWK? At $349.95 for the linkage
system and $120 for a new shock spring, this is an
expensive mod. In many cases, going down to a softer
shock spring can lessen some of the KTM’s suspension
woes at a cheaper price.
Every MXA test rider preferred to race with
PRO CIRCUIT 2016 KTM LINKAGE SYSTEM
the plusher Pro Circuit linkage system.
MXA TEAM TESTED