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Fox Launches New DH Suspension

March 26, 2013


Using feedback directly from athletes on the World Cup circuit, FOX introduces a completely redesigned 40 fork and DHX RC4 shock.

Scotts Valley, Calif. FOX—the industry-leading ride dynamics company—has announced the release of two 2014 gravity offerings with the 40 FLOAT RC2 and DHX RC4. The 40 utilizes an air spring and lightweight chassis and the DHX RC4 offers improved damping circuits and new adjustments.

Taking a clean slate approach and two years of development through FOX’s RAD (Race Applications Development) program, the 2014 40 FLOAT RC2 features a completely redesigned chassis and FLOAT air spring, dropping over a pound of weight from the previous model. The new chassis has the same strength as the previous design but all of the major components—the lower legs, crowns and upper tubes—have been optimized to lower the fork weight to 5.98 pounds (2711g). The FLOAT air spring is not only lighter than a coil system, it also offers incremental spring tuning and the addition of an adjustable compression ratio to modify the progressiveness of the spring curve.

The 2014 DHX RC4 borrows technology used in FOX’s Podium motorcycle shock. The damping loads between the main piston and reservoir piston are balanced to provide a more sensitive feel and better responsiveness to direction change. In addition, the shaft diameter has been decreased to ½”, which decreases friction and increases traction.

2014 40 FLOAT RC2 & DHX RC4

  • Two years of development
  • Clean slate design approach
  • Worked with key athletes to gain valuable feedback
    • Trek World Racing
    • GT
    • Santa Cruz Syndicate



  • All FOX products run through this program during development in one form or another
  • Competition is where products are truly tested and sorted
  • Most products will be in the field for one full season before going to production
  • We only use our elite athletes in this program
  • 40 and DHX RC4 developed through RAD program





» Design and tune front and rear suspension as a system
» Improve damping control
» Increase responsiveness and sensitivity
» Win races



ESC Pro GRT Plattekill-5240

  • During the 2011 season, RAD program looked to revise shock
  • Experimented with different chassis designs
    • DH bike linkages began building progressiveness into design
    • Less need for progressive damping system


Changed damping system

  • New frame linkage design required more linear shock tune
  • Used damping information we learned from Podium moto shock to help tune

Reduced shaft diameter from 5/8” to 1/2”

  • Decreased friction
  • Improved sensitivity and responsiveness
  • Riders noted increased traction, feeling of more travel


  • February 2012 began racing new design
  • Proto DHX RC4 on bikes that won:
    • 2012 Men’s World Championships
      • Greg Minnaar
    • 2011 and 2012 World Cup Series
      • Aaron Gwin
    • Top 5 Men’s podium, first and fourth Women’s podium at Val di Sole, Italy, World Cup.
      • Aaron Gwin won by 7.85 seconds
1ST Aaron Gwin
2nd Greg Minnaar
3rd Gee Atherton
4th Marc Beaumont
5th Cameron Cole
1ST Rachel Atherton
4th Florian Pugin

 2014 DHX RC4

Key features

  • High-speed and low-speed compression and rebound damping adjustments
  • Air assist and air assist volume adjusters to fine tune the spring rate and progression
  • 1/2” shaft
    • Reduced friction, improve small bump compliance
    • Increase oil volume
  • Redesigned valve system






  • Design and tune front and rear suspension as a system
  • Large weight reduction; low center of mass
  • Improved handling; tuned stiffness from key components
  • More tunable spring system
  • Higher performing damping system
  • No compromises
  • Win races


  • Winter 2010 FOX undertook an initiative to study chassis design
    • Built an inverted fork design to compare to the current 40
    • Inverted design featured 36mm stanchion
    • tubes, 48mm outer legs and used a 40 FIT
    • damper and titanium spring system
    • Tested with key athletes, mainly Aaron Gwin and Gee Atherton




  • Inverted fork showed great fore and aft stiffness but poor lateral stiffness
  • Conventional 40 fork provided good fore and aft stiffness and great lateral stiffness
  • We worked to improve the performance of the inverted fork with a stiffer axle assembly
    • Determined we could not greatly improve the lateral stiffness while using the industry standard 20mm axle or without greatly increasing the weight of the fork
  • FOX athletes chose conventional design of the 40 over the inverted chassis
    • Conventional design offered more desirable handling characteristics at a lighter weight and lower center of mass


  • RAD program determined the need for a more progressive air spring
    • 2011 WC season started testing coil/air spring system internally called PABLO.
    • PABLO stands for Pneumatic Assist Bottom Load Optimizer
      – it became more of a name than an acronym
    • PABLO system seals off lower leg assembly so the fork builds airpressure during compression to provide a progressive spring rate
    • RAD athletes raced on PABLO spring system in 2011
      • Aaron Gwin won five World Cups and the World Cup Series on it



  • PABLO spring system was good but we wanted more tunability
  • While redesigning our 2013 FLOAT air springs we developed one for the 40
    • A lot of work went into tuning negative spring system
    • Developed adjustable compression piston to tune progressivity
    • Float is lighter, more tunable and relieves work of damper



  • Tuned to match FLOAT air spring
  • Eliminated hydraulic bottom-out
    • Not needed or desired with air spring design
  • RAD athletes all used same damper


ESC Pro GRT Plattekill-4948

  • Held test sessions with RAD athletes at Leogang and Plattekill during the same week
  • At the next World Cup Downhill race in Val di Sole, Italy, riders on proto Air 40s took first through fifth on the men’s podium, and first and fourth on the women’s podium
    • Aaron Gwin won by 7.85 seconds

2014 40 FLOAT RC2

Key Features

  • Air pressure spring adjustment (45 psi to 80 psi)
  • Adjustable air spring compression ratio – nine positions
  • High-speed and low-speed compression and rebound damping adjustments
  • 203 mm of travel



2014 40 FLOAT RC2


Structurally optimized crowns to save weight

  • Bending and torsional stiffness the same as 2005-2012 40
  • Lower crown pinch bolts moved to front to increase steering clearance

2014 40 FLOAT RC2

Butted upper tubes

  • Bending and torsional stiffness the same as the 40 from 2005-2012

2014 40 FLOAT RC2

New lower legs design

  • Bending and torsional stiffness the same as the 40 from 2005-2012
  • Full web truss arch design is the ultimate in lightweight fork brace design
  • Air bleed system to relieve internal air pressure from elevation changes
  • New axle pinch bolt design
  • DH post mount brake design

2014 40 FLOAT RC2

40 FLOAT air spring


  • Allows easy tuning for a wide range of riders
  • Low friction linear air spring in first half of travel
  • Progressivity in the second half of the spring curve internally adjustable via compression piston position
    • Has nine positions

2014 40 FLOAT RC2

Redesigned FIT RC2 damper

  • Tuned to match FLOAT air spring
    • No hydraulic bottom out
  • Kashima coated shaft

Marc Landry is a Toronto, Ontario based action sports photographer. Honing his skills on local and World Cup cycling circuits, Marc has since expanded his subject matter to include several outdoor adventure sports. Marc is in his element when surrounded by the energy that top athletes radiate. The relationships he forms with his subjects is apparent in his images and is part of what defines his look. He is most at home in the mountains and his preference for long glass and elaborate lighting setups has become his signature style.

Fox 34


  1. Wow, what an article!

  2. That’s a serious diet for the 40 – 1 pound? wow!

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