MXA TEAM TESTED: PRO CIRCUIT YAMAHA YZ450F SHOCK LINKAGE

September 21, 2011
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WHAT IS IT? An aftermarket shock linkage for the 2010-2011 Yamaha YZ450F that alters the rising rate, kicks out the head angle, lowers the seat height and helps balance the chassis.

WHAT’S IT COST? $224.95.

CONTACT? www.procircuit.com or (951) 738-8050.

WHAT STANDS OUT? Here’s a list of things that stand out with the Pro Circuit YZ450F shock linkage.

(1) Link theory. In its simplest form, a shock linkage compresses the shock from the bottom while it is being compressed from the top by the energy of the bump. What is typically ignored is the affect a shock linkage has on the bike’s chassis. MXA test riders have always been concerned about the stinkbug setup of the CRF450, KX450F and YZ450F. This “tall in the rear” feeling isn’t just an irrational perception?it can be measured. In stock trim, the 2010 and 2011 YZ450Fs tend to stinkbug in motion. The rear stays high, while the front is low. This causes the head angle to steepen every time you decelerate. The result is a strange wiggle on the entrance to corners. The weird seesaw sensation isn’t a deal breaker, but unnerving.

(2) The fix. The fix is as simple as mounting a longer link arm on the YZ450F’s bell crank. The longer arm achieves three things: First, it stiffens up the initial part of the linkage’s rising rate curve (longer arms don’t change the bell crank-derived curve; they only change the starting point). Second, a longer link arm lowers the rear of the bike, which in turn kicks out the head angle to allow for more setup possibilities. Third, with the rear of the bike lower, the rider can slide his forks up and down in the triple clamps to tune the handling and eliminate the wiggle.

(3) Numbers. In the world of shock linkages, Pro Circuit knows what it is talking about. Most factory race teams run a Pro Circuit link or a copy of one. By lengthening the YZ450F linkage arms by 1.5mm, Pro Circuit is able to lower the seat height by 10mm and stiffen the initial part of the YZ450F’s stroke to hold the YZ450F shock higher in its stroke longer.

(4) Handling performance. You might think that the Pro Circuit link is a suspension device. Not really. Its greatest attribute is what it does to the bike’s handling. Lowering the rear of the frame kicks out the head angle, which can then be set across a wider window by raising and lowering the fork height. As the overall chassis height moves down, the cornering improves enough to calm down the twitchiness. The longer link allows the rider to adjust the handling by changing the fork damping, fork leg height and rear sag to get a calmer and more refined chassis.

(5) Suspension performance. The longer linkage arms rotate the bell crank deeper into its stroke, which translates into stiffer initial suspension, because it starts later in the curve. The result is a much more balanced chassis, a rear suspension that stays higher in the stroke, more usable travel and more setup options (front and rear).

WHAT’S THE SQUAWK? The Pro Circuit link slips right in place of the stock linkage, but take care when installing it. There are loose needle bearings that can be dislodged by rough handling during installation.

Every MXA test rider liked what the Pro Circuit linkage did for the YZ450F (and chose to run it). It isn’t as noticeable an improvement as on the 2009-2011 Honda CRF450s, but if the twitchiness on the entrance to turns bothers you, the link will eliminate it.

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