Husqvarna is offering three four-stroke motocrossers for 2021—the FC 450, FC 350, and FC 250. The three models share the same chassis, with the FC 450 having a SOHC motor that is distinct from the DOHC powerplant used on the FC 350 and FC 250. Most of the changes for ’21 are chassis related, so let’s go over what’s new.

1.The WP Xact fork gets a makeover for 2021. The outer tubes and fork damping cartridges are 10mm shorter, which adds rigidity. There is also a new mid-valve damping system on the air-spring Xact fork, with the goal of softer performance on landing from big air due to reducing pressure peaks in the internals.
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https://ultimatemotorcycling.com/2020/07/11/2021-husqvarna-4-stroke-motocross-lineup-first-look-5-fast-facts/