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motocrossactionmag.com

MXA TEAM TESTED: JGRMX ADJUSTABLE YZ-F/RM-Z ADJUSTABLE PULL-RODS

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JGRMX-LINK-1WHAT IS IT? The JGRMX YZ250/450F adjustable shock linkage system not only lowers the rear of 2010–2017 YZ450Fs and 2013–2017 YZ250Fs but also the 2017 RM-Z250 and 2017 RM-Z450. As with all links, it stiffens the initial part of the shock’s stroke while lowering the seat height. What makes the JGRMX shock linkage unique is that it allows the rider to go as low he wants to go.

WHAT’S IT COST? $279.99.

CONTACT? www.jgrmxstore.com or (877) 905-4769.

WHAT STANDS OUT? Here’s a list of things that stand out with the JGR adjustable YZ450F link.

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(1) Function. The rising-rate linkage on your bike makes it possible to manipulate the suspension curve to put more or less leverage on the shock by increasing the speed of the shock as the rear wheel moves through its arc. Got that? It does this by changing the amount of shaft travel per increment of rear-wheel travel. The linkage ratio makes the shock’s valving work more effectively when the situation calls for a stiffer response.

(2) Design consideration. It is important to note that a complete rising-rate system consists of a bell crank (that the shock attaches to) and a linkage arm (that positions the bell crank in relationship to the frame). Motorcycle manufacturers are constantly changing their rising rates by changing the eccentric cam shape of the bell crank; however, adding longer or shorter linkage arms does not actually change the rising rate as much as it changes the starting point where the rising rate begins on the bell crank. JGR’s adjustable pull rods enable a rider to increase the length of the link in 1mm increments on the YZ-F and 0.5mm on the RM-Z. On the YZ-F, this means from 142mm to 146mm (the JGR riders ran their links at 144mm when they raced YZ450Fs) and on the RM-Z from 132mm to 134.5mm (Weston Peick runs his RM-Z450 link at 133.5mm). As the length of the linkage arm is increased, the rear of the bike gets lower because the bell crank and the shock attached to it are rotated down. By moving the bell crank’s eccentric cam, the starting point of the rising rate is moved into a stiffer point of the curve. This makes the bike slightly stiffer during its initial movement to help lessen wallowing.

(3) Installation. The JGR adjustable linkage mounts like any other aftermarket linkage, with the exception of the snap-in inserts that go in the rear-link bolt holes. These inserts are drilled at different offsets to make the arm go from the stock length to 4mm longer. As for lowering the rear of our YZ450F, 1mm shorter will lower it 8mm, 2mm will lower it 14mm, 3mm will lower it 19mm and 4mm will lower it 23mm.

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(4) Performance. The MXA wrecking crew loves longer links on the YZ-F and RM-Z, not only because they lower the rear of the seat, but because they can be used to change the chassis head angle and overall height (when used in a comprehensive plan with fork-leg height). Most MXA test riders ran it at 2mm longer, but short riders went with 3mm. MXA considers a longer link to be a handling modification instead of a suspension modification. By lowering the rear, you lessen its irritating stinkbug stance, and as the bike gets lower, its cornering ability improves noticeably.

WHAT’S THE SQUAWK? You can’t just bolt the JGR link on and forget it. You will need to lighten the high-speed compression by as much as one turn (the shock will feel stiffer with the longer link), reset the sag and slide the fork legs up in the clamps to reset the balance of the chassis. The ultimate goal is to get the bike flat.

MXA RATING: The JGR linkage arm solves problems for riders looking for a lower seat height, firmer initial compression damping or lowering both the front and rear of the bike to get the chassis to handle better.