Fork Free Piston Tech Specs  (Updated 4/26/2020)

Current twin chamber (aka closed cartridge) forks are pressurized dampers similar to the rear shock of the motorcycle.  KYB, Showa, & now WP twin chamber forks apply pressure against the cartridge rod (damping shaft) using a linear rate compression spring & free piston divider to account for the volume change of the oil displaced by the cartridge rod during compression.  During 2007-2014 WP twin chamber forks (aka bladder fork)  use a gas pressurized bladder (membrane) which has certain advantages and functional drawbacks.

 The functioning difference between a 2006-2018 KYB free piston assembly design and Showa free piston is KYB pistons isolate the "pressure spring air" from the "outer chamber air".  When the fork compresses the "outer chamber air spring" builds pressure, this pressure does not add to the free piston spring's pressure on the cartridge rod.  In short, there are two separate air spring chambers, the free piston pressure spring air and the main spring outer chamber air.  Rumor on the street is that KYB had to work around a Showa patent resulting in this design.

KYB Free Piston

Why do KYB free pistons often break, grenade, explode, crack, shatter, fracture, split,......???

• Faulty free piston seal allows piston to fill with fluid with no drain/blow-off
• Unbalanced valving
• Fast and/or heavy rider on suspension not setup for them
•  Weak plastic piston from lack of fork maintenance