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New Fox Shocks FIT Damping System and Boost Valve Tech

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BIKERUMOR.com 2009 SEA OTTER CLASSIC COVERAGE: Fox Racing Shox is introducing the FIT (Fox Isolated Technology) damper into their full range of shocks. Previously, the FIT damper, was available in their 36- and 40-series forks (the number refers to the stanchion diameter), but not their 32-series.

The FIT replaces an open bath oil/air damping system with an enclosed cartridge that keeps air from mixing with the oil.  The main benefit is it provides more consistent damping through a wide range of temperatures since the oil can’t compress like air can, and it’s not as sensitive to changes in temperature. In other words, the fork will work better regardless of the weather and after a long ride when things inside may heat up.

The other benefit is lighter weight. Because the forks aren’t running a full, open bath of oil, they can use less oil…thus, less weight.Fox reps said this should translate into the wheel sticking to the trail better because of A) better performance and B) less unsprung weight. Click on the images to enlarge some cutaways

2010 fox shocks fit damping system bicycle suspension forks and shocks2010 fox shocks fit damping system bicycle suspension forks and shocks2010 fox shocks fit damping system bicycle suspension forks and shocks2010 fox shocks fit damping system bicycle suspension forks and shocks

Another new technology making its way into their shocks is Boost Valve. Hit “more” to learn about that and get detailed specs and photos…


The full range of Fox suspension forks now have FIT as an option, with the following disclaimers:

  • The 32-F RLC will come standard with FIT
  • The 32-F RL Remote (remote lockout) models will not have it, but they hinted it could come later
  • The 32-F RL was up in the air. Some of their reps said OEM only will come with the FIT, others said aftermarket units will come with FIT. Stay tuned…or just get the top-of-the line model and you’ll be happier anyway.
  • The 32 Float and TALAS models will get FIT

Forks with FIT will start shipping in a few weeks and be readily available by late May.


This is what the FIT cartridge looks like and where it goes. Mechanically, it required moving some of the controls around. The Lockout Threshold adjustment moves to the top, and the Rebound adjustment moves to the bottom of the leg (red knob).


Fox says it made more sense to move the Lockout Threshold control to the top since riders are more likely to fiddle with those settings during a ride than Rebound damping settings. The Lockout Threshold acts like a top end compression adjustment. With it fully on, when you lockout the fork, it ain’t gonna budge except on a massive strike. With it fully off, it’ll be firm but the lockout will give a little. For climbing, that would be a preferable setting since it keeps things efficient, but allows some of the bumps to go away.


Top left knob now has lockout, lockout threshold and compression damping adjustments on the top. Right side cap conceals the air valve.

Other updates:


  • All shocks across the line will have 1.125″ to 1.5″ steer tube options
  • All shocks will have standard QR or 15mm axle options
  • These options include the 29er forks


soc09-fox-shocks_18 soc09-fox-shocks_19

This is the Boost Valve. The silver piece moves up and down ever-so-slightly, per below:


When it’s closed (top), it creates a flat surface that shuts off the flow of oil. When it’s open (bottom), it lets oil flow through. The Boost Valve will be available on the Fox Float RP line of shocks, and it basically serves to improve the ProPedal platform’s performance and increase end-of-stroke bottom out performance.

In other words, the big hit bottom out compression is now handled by Boost Valve, letting Fox engineers soften up the ProPedal damping to be more responsive. On ProPedal settings 1 and 2, suspension movement will blow through the PP damping first, then put the Boost Valve to work. On setting 3, it’ll blow through Boost Valve first, then PP damping. The result is a still-firm-for-pedaling platform, but one that’s more sensitive to small bump forces. All that should equal a smoother shock that’s less likely to bottom out. Giant’s pro rider Adam Craig has been testing one and seems to like it.

(NOTE: I would have a picture of the new DHX RC4, but a Fox rep grabbed it as I was taking notes and started showing it to a foreign journalist. He wouldn’t give them back.)

On the downhill side, Fox has a new shock called the DHX RC4. Coming in May, it was designed with input from Gee Atherton who won a World Cup on it. Based off their existing designs, it changes the following:

  • Increased oil capacity and flow through the end cap assembly
  • Modified Boost Valve with progressive damping at end of stroke
  • External Bottom Out control knob
  • No Pro Pedal, replaced with separate external High and Low Speed Compression controls
  • About $580 MSRP

They’ll also offer an RC2 that’ll be OEM spec only that won’t have the Bottom Out control.


Fox also announced that they’ll offer Pro Tune service to any consumer who wants to upgrade the performance of an older shock by helping them set it up correctly for the bike it’s on. If “consultation” doesn’t get it right, you’ll have the option of sending your fork or shock in for factory Pro Tuning. Besides getting it back with the settings dialed in just for you, it’ll have some fancy new stickers so all your friends know you’re special, too.

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