MXA TEAM TESTED: PRO CIRCUIT 2017-18 HONDA CRF450 LINKAGE
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 2017-18 Honda CRF450 shock links.
(1) Purpose. A longer shock link can alter a bike’s rising rate, kick out the head angle and lower the seat height. Since the 2017-18 Honda CRF450 has a stinkbug stance and tends to wallow in the initial part of the stroke, a lower shock link can address these issues. The Pro Circuit 2017-18 Honda CRF450 link arms are 1.5mm longer than the stock 144mm link arms. The Pro Circuit link lowers the rear of the bike by 12mm.
(2) Linkage theory. Shock linkages work by compressing the shock from the bottom while it is being compressed against the top shock mount by the energy of the bump. By altering the speed of the shock per millimeter of stroke, damping is increased as the shock moves upward. How it does this is very simple. Since the orifices in the shock piston are fixed, they flow more shock fluid at low speeds than they can at high speeds. As the shock shaft speed increases, the fluid can’t get through the orifices as fast, thus the flow rate is impeded, much like trying to push a 10-pound pig through a 5-inch hole in a fence. The harder you push, the slower the pig goes. In action, changes in the speed per millimeter allow 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.
(3) Rising rate. The speeding up of the shock as it moves upward is called rising rate. It is common practice for the manufacturers to change the rising rate to solve suspension issues. For example, if a bike bottoms excessively over big jumps, the engineers will make the shock resist bottoming by making the shock move faster in the final third of the stroke. Conversely, if a shock is too stiff at the end of its stroke, the engineers will go to a less progressive rate change to make the suspension feel plusher.
(4) Linkage arms. It is important to note that rising-rate changes are achieved by the eccentric cam of the shock linkage’s bell crank, not the linkage arms. Longer link arms do not change the rising rate. Instead, they change the starting point of the shock on the existing leverage curve. The longer arm achieves this by rotating the bell crank slightly higher in its arc. In effect, installing longer link arms makes the shock feel stiffer initially without changing how it feels later in the stroke. At the same time, longer link arms lower the rear of the bike.
(5) Performance. Before MXA resorted to a longer link, we were shortening the CRF450’s Showa shock. This was a drastic solution for a shock that was already 45mm shorter than the year before. The Pro Circuit link lowered the rear of the seat, increased compression damping in the initial part of travel and gave us more tuning possibilities. With the link installed, we slid the forks up 2mm to keep the same head angle, lightened the high-speed compression and reset the sag. Overall, every MXA test rider preferred the 2017 CRF450 with the Pro Circuit link.
WHAT’S THE SQUAWK? No complaints.
MXA RATING: It no secret that the 2017-18 CRF450 has suspension issues, both front and rear. On the 2017 model many of these ills can be alleviated by stiffer fork and shock springs, but springs don’t address the seat height, chassis setup or wallowing problems. The Pro Circuit link does.