Last year, speculation ran rampant when pictures of what appeared to be a prototype Fox 40 began to make the rounds on several social networks. The new fork quickly appeared on the front of every elite Fox sponsored athlete’s bike and went on to accrue an impressive array of podiums over the course of the season.

So what’s new? We recently met with Mark Jordan, Fox’s Global Marketing and Communications Manager, to discuss the new products. Head past the break for the details…

Revamped DHX RC4

It’s hard to get excited about a coil shock in this brave new world populated by ultra lightweight downhill bikes (that frequently weigh less than the trail bike in my garage), but as modern frames have evolved, so have the demands placed on the  rear suspension. So Fox has spent the past two years completely overhauling one of the best performing shocks on the market to match recent trends.

The suspension engineers at Fox have had the advantage of working with some of the premiere World Cup Downhill teams during the development phases of the next generation of frames. During the testing and prototype phases, the company performed extensive chassis studies, and determined that these new frames were being developed with more progressive linkages that demanded different tuning characteristics.

Cutaway of the newly redesigned Fox DHX RC4

The new rising rate linkages eliminated the need for more progressiveness shock damping, which took load of the damper, and left more room for fine tuning. So Fox engineers took lessons they learned developing their Podium Moto Shock to redistribute  and better balance the damping loads between the main and reservoir pistons while maintaining a similar dyno curve.

In an effort to reach this goal, the diameter of the shaft was reduced from 5/8″ to 1/2″. The reduction in surface area lead to a big decrease in friction and riders claimed there were significant improvements in sensitivity and responsiveness. The smaller diameter of the new shaft also reduced the initial break in period.

Before, the old shock could be made more progressive by changing the air pressure in the reservoir and dialing in the bottom out resistance. With the new shock, which has less progressive damping built in, the adjustments act differently.

Instead of a boost valve, the shock features an air assist which can operate between 125 to 200 Psi. Stock is usually 175, depending on the frame and rider. Since stock springs are sold in 50 lb increments, if you’re in between, the new air assist allows you to set the shock exactly where you want.

40 Float RC2

The big announcement this year is the all new downhill fork. Two years ago Fox wanted to redo the chassis with the goal of reducing weight and increasing performance in a few key areas, e.g. adjustability.

They performed several chassis tests to compare the advantages of conventional and inverted forks and the advantages of using a hybrid coil and air system. The inverted chassis they tested featured 36mm stanchion tubes, 48 mm outer legs, and used a 40 FIT damper and titanium spring system. Working with Aaron Gwin and Gee Atherton, they determined that the inverted designed suffered from poor lateral stiffness and couldn’t offer the level of handling the athletes desired. Improving the lateral stiffness would have made the fork too heavy. Furthermore, the conventional design had a lower center of gravity.

Over the course of the past two seasons, Fox began testing prototype air systems in their conventional fork chassis. Their first attempt, a coil/air spring system code named PABLO (for Pneumatic Assist Bottom Load Optimizer), was tested extensively during 2011, and Aaron Gwin won five World Cups and the World Cup Series on it. The PABLO system worked by sealing of the lower leg assembly so that the fork built air pressure during compression to provide a progressive spring rate, but the engineers wanted more tunability.

(Right to Left) Top Cap assembly, the shaft which holds the compression ratio adjuster assembly, four spacers, the compression ratio adjuster (in position five), four more spacers, and the black aluminum bolt on the end.

In order to build in that tunability, Fox developed a new Float cartridge with an adjustable compression piston to tune progressiveness   The new air spring compression ratio adjuster sits underneath the top cap assembly and is easy to adjust. The piston has 9 different positions. By re-configuring the spacers you can move the compression ratio adjuster up or down  to increase or decrease the air volume, which affects the character of the air spring.

The stock tune is five and at the highest level it’s feels closest to the coil sprung fork. One of the main advantages of the adjustable air piston is that riders can tune the fork to help them maximize their travel.

Taking lessons from their inverted chassis study, Fox also tuned the fork to be more laterally compliant. The new crowns have the same ultimate strength, but were leaned out, because the top athletes didn’t need (or necessarily want) the additional stiffness from the cross bracing.

The pinch bolts were also moved from the back to the front to increase the turning radius and lean out the crowns a little bit more.

The new lowers incorporate an air bleed system to relieve internal pressure from drastic changes in elevation and temperature. Otherwise, the air pressure inside the fork can increase by 3-5 Psi from sea level to the top of the lift, which squeezes the seals and increases friction.

The new 40 Float features redesigned lowers. Major advancements in casting technology allowed the designers to shave 150 grams from the lowers. The axle pinch bolt system was also redesigned to make it lighter and easier to extricate stripped bolts.

The Rumor Mill…

A 27.5 version of the fork is currently in the works and will be available by mid year. The tweener fork will feature the same internals but different lowers, so you’ll easily be able to convert your 40 Float. Since the new Fox 40 Float RC2 has increased marginally in price, the company will also be offering an entry level R model for OEM spec, and possibly after market sales.It is possible to retrofit existing Fox 40s with the new air damper, but no word on pricing or availability of the new kit.






  1. Fork MSRP= $1700. With the prices of DH bikes these days, why not just buy a dirt bike? Motorcycles don’t depreciate like mountain bikes and they don’t need to be shuttled uphill. If you are not gonna pedal uphill, dirt biking is cheaper in the long run.

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