WHAT IS IT? Stiffer clutch springs for modern
WHAT’S IT COST? $69.95 (most models), $79.95 (2013–
’ 15 CRF450, 2005–’ 15 RM-Z450, 2010–’ 15 YZ450F).
CONTACT? (951) 738-8050 or
WHAT STANDS OUT? Here’s a list of things that stand
out with Pro Circuit’s works clutch springs.
(1) Function. Do you know how a clutch works? It
is a simple mechanism. A clutch consists of 16 spinning
discs. Half of the discs are coated with fiber, and the
other half are bare metal. The metal discs are connected
to the transmission, and the fiber discs are connected to
the engine. When the 16 discs are pressed together, the
power from the engine is transferred to the transmission.
It goes without saying that when the 16 discs are
separated, the tranny and the engine are disconnected.
To make a bike move, the eight fiber discs have to grab
onto the eight metal discs and stay connected via friction.
The firmer the contact between the 16 plates, the more
positive the drive to the rear wheel.
( 2) Common bond. What holds the 16 discs together?
Five little coil springs. No matter how much power your
motorcycle produces, if it weren’t for those five springs,
you wouldn’t move a single foot. This clutch arrangement has worked flawlessly for decades, but modern
four-strokes have added a new dimension to the life of
a motorcycle clutch. With its massive increase in torque,
flywheel weight and crank inertia, a four-stroke puts a
greater load on a motorcycle clutch than a two-stroke.
The problem is that most 250cc four-stroke race bikes
use a clutch designed for a 125cc two-stroke, while 450
four-strokes run 250 two-stroke clutches. Not good, and
especially not good if the four-stroke rider tries to apply
clutch-heavy two-stroke tactics to his thumper. Can you
smell what you’re cooking?
( 3) Spring rate. Pro Circuit’s clutch springs are 15
percent stiffer than the stock clutch springs. What does
that mean? Pro Circuit’s springs press the 16 clutch
plates together with 15 percent more pressure than the
( 4) Clutch pull. The Pro Circuit clutch springs make
the clutch lever harder to pull, but this is only a concern
for a 10-year-old Girl Scout, not a manly motorcycle racer.
WHAT’S THE SQUAWK? If you are a clutch
abuser, stiffer springs won’t be enough; you’ll need to
call Hinson for the high-priced solution.
The manufacturers are so concerned with
having an easy-pulling clutch on the showroom
floor that they compromise performance on
the track. The bikes that benefit most are the
Kawasaki KX250F/450, Suzuki RM-Z250/450
and Honda CRF250/450. KTM doesn’t need help.
PRO CIRCUIT WORKS CLUTCH SPRINGS
MXA TEAM TESTED