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motocrossactionmag.com

FORK WORKS: RIDE JBI PRO PERCH 2.0 FORK MODS|Motocross Action Magazine

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The Ride JBI Pro Perch is a fully modified, high-performance spring seat that replaces the stock spring seat on Showa, Kayaba and WP forks. The MXA test crew elected to test the JBI spring perch on our 2018 Honda CRF450 Showa coil-spring forks. When testing the stock 2018 Honda CRF450, every test rider complained that the Showa forks were very harsh through the small bumps, but too soft over big humps. They chattered in the braking bumps and dove excessively in big landings. This is a hard problem to solve, because the forks are both too stiff and too soft at the same time. For 2018 Honda upped 2017’s fork spring rate from 0.48 kg/mm to 0.50 N/m. Common sense would lead most CRF450 racers to believe that the 2018’s stiffer fork springs would make the forks resist bottoming. Not so. Worse yet, the stiffer fork springs are a major contributor to the harshness early in the stroke.

Our backyard solution was to add 10cc of oil to each fork leg. What would that do? It would stiffen up the last 4 inches of fork stroke to alleviate bottoming and allow us to turn the compression clickers out to soften the first part of the stroke for the braking bumps. As with all Band-Aid fixes, it worked, but it was not the best solution. We think that the source of the problem is Showa’s 2018 compression damping. In particular, we think the fork needs more mid-stroke compression to help control the speed at which the fork plummets towards bottoming. This is where the Ride JBI Pro Perch 2.0 comes into the picture.

The objective of a fork’s spring seat (or spring perch), apart from the fork springs sitting on it, is to flow oil through the system. The rate at which the oil flows depends on the spring seat’s orifice sizes. Showa’s 2018 Suzuki RM-Z450 and CRF450 forks have large ports that allow for the free flow of oil. Conversely, Ride JBI’s spring seat meters the oil flow through the spring seat with ports that are controlled by flexible reed-valve shims. The shims allow for a speed-sensitive flow of oil through the spring seat. At slow fork speeds, the shims flex less, allowing less oil to flow through the ports. At high speeds, the shims bend out of the way and open up the ports. In simple terms, the JBI’s shims open and close based on the oil pressure created by fork movement. This “active” style of damping at the spring perch results in a fork that is plush in small bumps yet firm enough to soak up hard hits and big landings without being harsh.

On the track, the Ride JBI Pro Perch solved our Showa problems on the 2018 Honda CRF450. It drastically improved the suppleness at the top of the stroke, smoothed out the mid-stroke and eliminated bottoming. As a result, we were able to run much softer compression settings than normal, and the clickers made a more noticeable difference.

What does it cost? The Pro Perch 2.0 retails for $285. If you are competent enough to change fork seals, you can install the JBI Pro Perch 2.0 yourself. If not, JBI will do it for you and re-valve your forks for $230 more. If you do it yourself, the oil height in the Showa forks needs to be reduced from 360cc to 320cc. For more information, go to www.ridejbi.com or call (480) 269-5585.

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