ASK THE MXPERTS: 2021-2022 WP XACT OFF-ROAD FORKS VERSUS SXF FORKS

The 2021-22 KTM, Husky and GasGas two-stroke and off-road forks now have the shim stack on the mid-valve.

Dear MXperts,
Looking for info on my 2021-2022 KTM 300XC. Do you guys know if the fork changes are the same as the ones you outlined in the February issue on the 2021 KTM 450SXF?

Yes and no. The KTM 300XC does get the totally revised fork technology from the 2021 KTM 250SXF, 350SXF and 450SXF, but there are a few differences. The KTM 300XC and Husky TX300 forks (and 125SX, 150SX, 250SX and 300SX forks) do feature the improved oil bypass notches and new air seal with air bypass holes. Both “bypass” systems were developed to reduce pressure spikes and create smoother and more predictable fork action. The forks also got the enlarged cross-over bleed slot, which allows air pressure to transfer from the positive to negative air chamber more easily. The negative chamber’s main job is to stop topping out. The 2021 WP XACT forks on all the bikes use the new bump stop rubber and adjust-by-hand rebound clicker. The valving is softer on the XC Float valve forks to work well in off-road, woods and rocky conditions.

The 300XC and TX300 also gets the two-stroke and off-road version of WP’s trampoline valve. If you’re up-to-date on the latest air fork technology, you know that the trampoline valve is located at the mid-valve shim stack, and it is designed to give air fork users the improved front wheel traction and predictability of a well-built spring fork; however, on the 300XC, the trampoline valve differs slightly from those on the motocross models. The cross-country forks (and KTM, Husky and GasGas two-stroke forks) don’t have a pure trampoline valve; instead, they have a float valve, also called a “lift-height component,” that allows WP to create softer suspension valving without excessively bending the shims.

Technically, on the motocross-oriented WP XACT fork, the trampoline shim is preloaded. When oil squeezes through the valve stack, the trampoline shim can bend into a cavity below it more than a normal shim. It’s called a trampoline shim because it flexes under oil pressure, much like a trampoline goes up and down under a gymnast’s body weight. The 300XC fork (and its Husky and GasGas brothers) doesn’t depend on the trampoline effect; instead, it has a light coil spring under the shim stack in a small cavity. This spring pushes against the shims for slight resistance on compression and to close off the shim stack on rebound.

Prior to the 2021 models, the XC models didn’t have a shim stack at the mid-valve to generate damping; instead, the damping was controlled by the base valve. With this design, the WP technicians weren’t able to create enough damping at the mid-valve on their cross-country forks because they couldn’t get the shims to be soft enough without bending or breaking them—so they were forced to bypass that part and depend on the base valve. The 2021-2022  WP XACT air forks on the cross-country, off-road and two-stroke models will work much better than last year’s forks because they won’t be creating all of the damping at the base valve. The new lift-height component will allow the forks to create damping at the mid-valve like on the motocross models.

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