Menu

2014 Fox 40 Float and DHX RC4

Riding Fox's New Air 40 and RC4 in the Rocky Mediterranean

Words by Morgan Taylor. Photos by Thomas Dietze and Morgan Taylor.
March 26th, 2013

It’s not really a secret that Fox had an air sprung version of their downhill fork in the works. At last year’s World Cup in Val di Sole, we saw a new lower assembly debut, with an air release valve on each side. Funnily enough, that air release valve is not at all related to the fact that the internals of the forks were different: firstly, the valve provides a function that is seen in MX forks; second, as you could guess, Fox had been testing air-sprung internals in their athletes’ bikes through their RAD (Racing Applications Development) program, but remained vague about the new spring.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

I arrived at La Fenosasa Bike Park under the cover of darkness, and woke up to a hazy sunrise over the pumptrack. Photo Morgan Taylor.

Earlier this month, Fox invited us to spend a couple days at La Fenosasa Bike Park near Alicante, Spain. From Vancouver it was three planes to get to Alicante, each one smaller than the last. Takeoff is my favourite part of flying, and landing is always unpredictable. The smaller the plane, the more hairy the touchdown – fitting that we were going to be smashing new DH parts in unfamiliar territory. With this thought as a backdrop I arrived at La Fenosasa in darkness, as the generator had been turned off for the night. My bag, with the majority of my riding gear, had been misplaced along the way.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Base camp at Fenosasa is a castle from the 1800s, on a generator for power meaning no heat or electricity at night. Very rustic. Photos Thomas Dietze / Fox.

The previous generation of 40 has been in production since 2005. RAD testing with the previous 40 and prototype springs determined that Fox’s racers wanted a more progressive feel in the new fork. Experiments were made with a “pneumatic assisted” coil spring, which did function quite well, but was going to be difficult to make much lighter than the existing 40, and didn’t quite have the fine-tuned adjustment between spring rates racers were looking for.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Greg Minnaar elaborates on his experience testing with Honda HRC and how that has informed his time with Fox. Photo Morgan Taylor.

What’s New with the 40?

The fact that this fork is going to be available soon is really just putting a date to an eventuality that you could guess about; it’s the details of the new internals that should be of interest. The three points Fox focused on when developing the new 40 were tunability, weight, and stiffness. For tunability they retain the RC2 damper’s wide range of clicks with a few updates plus a highly-tunable air spring system; weight of course comes down; and stiffness has decreased to make the fork more compliant.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Completely revamped from the ground up, the new 40 comes in under 6 pounds.

We can start with the stiffness discussion as that is the one that likely will raise the most eyebrows upon initial mention. It should be acknowledged that the existing 40 chassis, in production since 2005, is really stiff – enough so that the feedback through Fox’s racers was that they wanted a more compliant fork. This has been accomplished through refinements throughout the chassis. There is less material in the lower arch due to a revamped web truss. The lower crown bolts have been moved to the front of the fork, allowing more lock-to-lock clearance and material relief. The stanchion tubes are now butted rather than straight.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Unfinished prototypes show off the hollowed out web truss which allows more torsional compliance while retaining the strength of the coil 40.

The above noted improvements in compliance relate directly to weight as well, and as expected, the 40 Float sheds a significant amount of it: 476 grams over its coil sprung predecessor. This has been accomplished through optimization in every nook and cranny of the crown, stanchions, and lower assembly, as well as the elimination of the coil spring. Coming in a hair under 6 pounds, Fox matches the weight of the air sprung Boxxer World Cup.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Whole lotta air springs.

Because the air spring necessarily creates a more progressive spring curve, the damper can do less work in controlling compression forces. As a result, Fox decided to do away with the hydraulic bottom out circuit that was necessary in the coil 40. The RC2 damper has also seen revisions, including a Kashima-coated damper shaft (that you’ll never see), sealed low and high speed knobs, less oil, and a lightened cartridge tune to accompany the more progressive spring.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

The heart of the 40 Float’s adjustable air spring. Pull the cap and switch the position of the o-ring and spacers to change the air volume.

Highly adjustable air springs are no doubt the future of racing, but the wide range of rider weight and riding style will make this a welcome feature on any rider’s bike. When the Santa Cruz Syndicate boys were asked for their thoughts on the new fork, the adjustability of the air spring came up numerous times. Peat noted that ride height is adjustable within the air spring, rather than solely through bar height. I put this into practice in the test sessions outlined below.

Fox 40 Float Numbers

Weight: 5.98 lb (savings of 476 grams over the coil sprung 40).
Models: 26” and 27.5” lowers will be available; crowns, cartridges, and tubes remain same.
Availability: Mid-summer 2013 for 26”, late 2013 for 27.5”
Price: $1700 USD

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

This is the negative spring, which allows the air spring a linear curve for the first half of its travel.

2014 Fox DHX RC4

The 40 isn’t the only Fox DH piece seeing an overhaul for the 2014 model year. As a response to DH frames being designed with more progressive curves in the linkage, Fox’s racers found a need for a more linear shock tune. The venerable DHX RC4 sees updated damping and an air assist chamber to adjust ride height between spring increments.

The biggest change from 2013 to 2014 in the RC4 is where the damping is actually happening. With the previous Boost Valve system, much of the shock’s compression damping was achieved as oil was forced through small ports between the main chamber and piggyback.

By reducing the main shaft diameter to 1/2” from the previous model’s 5/8”, a greater proportion of the damping occurs in the main chamber of the shock rather than up in the piggyback. The smaller shaft has resulted in less internal pressure in the shock, which means less friction on the seals. All in all, a smoother, more adjustable shock to accompany the new 40.

Price: $600 USD
Availability: May 2013

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

2014 DHX RC4. More damping in the main chamber, and less friction as a result.

The Setup

In order to ensure the media would be testing the new parts on a familiar platform, we brought our own downhill bikes to Spain. Logistics aside, this was a great move as we spent half a day riding our existing setups and tuning to the local track before swapping to the new Fox bits for the next day and a half. I have been riding the 2013 Norco Aurum Dorado here on the Shore for the past few months, and was stoked to see how it would perform in uncharted territory.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

The Aurum with new Fox suspension bits, looking down over the town of Banyeres de Mariola. Photo Morgan Taylor.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

The RC2 damper has been updated to complement the progressive air spring, but still retains its many clicks of high and low speed damping. Photo Morgan Taylor.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Clamp bolts have been moved to the front of the crowns to allow more lock-to-lock clearance. Photo Morgan Taylor.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

And now the lower decals are on an angle just like the pros. Photo Morgan Taylor.

The Ride

The tuning process we went through was similar to what Fox does with its athletes and with product managers choosing stock spec for different models. We spent an entire day running the same track, giving feedback and measuring fork travel after each run, making small adjustments to deal with whatever issues arose.

The track itself, simply called “Number 6″, was very rocky and not very steep off the top, but wide open meaning speeds were high and the rocks were punishing. Through the middle there were some jumps, rock drops, and berms, but the general feel of the track was bumpy-as-all-hell. Great testing grounds for DH parts.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

La Fenosasa is a shuttle accessed bike park. We spent our days in these diesel Nissan military trucks, which trundle up the hill with nine bikes and riders. Photo Thomas Dietze / Fox.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

The bumpy first straight on Number 6. Loose as a goose. Shout to Mark Jordan and Chris Trojer for setting me up with riding gear as my helmet was all I had in my carry on. Photo Thomas Dietze / Fox.

Getting into that bumpiness, I found the bike initially was hanging up on square edges and riding a bit harsh. We made a few runs on the stock setup and tuned out my complaints. With the new 40 Float and DHX RC4 fitted to the Aurum, we changed settings by just one or two clicks at a time over successive runs, getting closer and closer to the ideal setup for the track.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Posing for a photo with the locals. Photo Morgan Taylor.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

This is about as much dirt as we saw on the trails at Fenosasa. Photo Thomas Dietze / Fox.

The result, through my feedback, was a bike that was very fast through the course, and on which I could feel the difference between a couple clicks of high speed and one or two psi in the air chamber.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Reporting back with Christophe and Bill after a run. Clipboards recorded each change and the rider’s impressions.

In this controlled environment, the range of the adjustable air chamber is definitely quite noticeable. With nine positions on the air spring, you can go all the way from a fairly linear spring rate (setting #1) to a very progressive one with big bottom out resistance (#9). The Fox engineers have a spring rate calculator that shows bottom out resistance at a particular chamber size and air pressure.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Changing the 40′s compression ratio is as easy as letting the air out of the chamber, pulling the top cap, and swapping some spacers.

When riding, I eventually settled on 71 psi in the fork at the #5 setting (right in the middle). At that point I decided it was time to try out the adjustable chamber. We switched the spacers to the #9 setting, full progressive, punched the new numbers into the chart, and decided on 68 psi which would still give me more bottom out resistance but potentially a more supple feel off the top. The difference was immediately noticeable. I ran a few laps on this setup and found the bottom out resistance to be significantly greater even at the reduced pressure.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

40 with an air spring cap.

The process of tuning suspension over successive runs is unbeatable for dialing in a setup. I can’t stress enough how much value there is in this process for racers, but even for the weekend warrior. Over two days of testing with the new 40 and RC4, both on my own bike and watching what the engineers were doing with others’ setups, Fox has definitely achieved their goal of adjustability along with the weight and stiffness.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Even the M820 Saint clutch derailleur was having trouble keeping up on the top section of Number 6. Photo Thomas Dietze / Fox.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

My bottom out tester, 10 feet high at the platform, more if you sent it too deep. Good place to feel the difference between air spring settings. Photo Thomas Dietze / Fox.

2014-Fox-DH-Launch-2

Long lens on the “North Shore”. Photo Thomas Dietze / Fox.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Joe Bowman of This Is Peaty was hanging out with the Syndicate boys snagging footage for the first episode of the season. Photo Thomas Dietze / Fox.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

And footage they did get! Minnaar and Bryceland were sessioning a new jump line, and Minnaar was letting it loose while wearing clips. Photo Thomas Dietze / Fox.

2014 Fox 40 Float Air DH DHX RC4 fork shock downhill bike Spain La Fenosasa

Bryceland gets crossed up at the top of Fenosasa. Photo Thomas Dietze / Fox.

The 40 has been and still is a product aimed at racers, and Fox’s RAD program ensures that racing keeps development moving forward. It’s been almost a decade since the original 40 was introduced, and Fox has definitely kept its sights set on the best performing product for its racers with the new 40 Float and RC4. We’ll be putting the new parts into long term testing duties back here in BC through the season.


Now that the cat is out of the bag, is the new 40 in line with your expectations? And would you send a superman on your DH bike?

  • stephenmatthews

    Air Morgan! That’s a rad shot of you sending it out.

    At least the trail shots make the ground look forgiving…not. That part of the world is terrifyingly rough on a bike, making it an amazing testing ground for suspension.

    • morgman

      When Greg Minnaar is complaining that his kidneys hurt, you know it’s rough. This was with respect to the other test track, Number 8, which had 50% more sharp chunky rocks than Number 6. He said it was a bit like Leogang in that you didn’t want to do too many practice runs as you’d wear yourself right out. It would take years to become familiar with a track at that rate…

  • PUNKY

    Did you have to shave the beard to fit into a full face?

  • Matt D

    Morgan JUST SENDIN IT

  • Midas

    Do they need a copy of my UCI Licence?

  • Dirk

    Are they sending out their full engineering team to help each purchaser tune up their new fork? This sounds awesome…but I’m not sure that testing a fork custom tuned by a team of suspension engineers says much about the experience the average user is going to see on this fork.

    • morgman

      The average user can do a number of things to replicate this process. First, finding a consistent track to run at least a few laps in a row. Second, writing down thoughts after each run. Third, bouncing these thoughts off someone else and only making incremental changes.

      I’m a huge supporter of having your suspension tuned professionally – it’s a small additional cost that has great bang for the buck. This camp was the fast track to getting that done, and in the process I learned a lot about the new fork and shock’s adjustment range which I was then able to pass on in this article.

      • Dirk

        Fair points.

  • Cheez1ts

    Clipped in superman with what looks like his hands coming off the grips!? I can’t wait to see the vidder of that one.

    Also, New fox stuff looks very appealing. I like what I’m seeing/reading.

  • satn

    Rock Shox now way behind