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2014 Fox 40 Float RC2 & DHX RC4

2014 Fox 40 Float RC2 & DHX RC4

Over the past two years the engineers at Fox have been working hard with their top riders to come up with something special, and the new air sprung 40 Float RC2 forks and DHX RC4 rear shock are the fruits of that labour.

Float 40 gallery

The new air sprung 40 has been completely reworked from the ground up. As you’d expect, the removal of a coil spring has automatically made this fork lighter than ever, but with a redesign of almost every single other component the fork is even lighter than you’d expect. At just a fraction under 6 lbs this fork is over a whole pound lighter than the 2013 40. Out of pure curiosity we also weighed a pair of the very first Fox 40’s which we have kicking around the office and those weighed nearly 2 lbs more than this new fork!

The full breakdown of the weight savings is as follows:

Air Spring: -152g
Lower Leg Casting: -150g
Upper Tubes: -89g
Upper Crown: -45g
RC2 Damper: -24g
Lower Crown: -18g
Steering Stop Bumpers: -4g

As you can see the new lower leg design have saved almost the same amount of weight as removing the coil spring, and the butting of the upper tubes has also saved a fair old chunk too. Of course though, weight saving is all well and good, but can this new air fork rival the coil 40? Well the guys at Fox seem to think so, and Deputy Editor Steve Jones has only recently got back from a sunny trip where he got to test them out himself. It’s obviously too early to draw any final conclusions, especially as these forks will have received royal treatment and will certainly not be ‘off the shelf’ units (as with most forks that we get to test out), but he did say that a couple of improvements were definitely noticeable.

The first is that the new chasis is more compliant, which is definitely a good thing. Don’t think that it’s not precise though, that’s just the same as before, as is the overall strength, but now there’s definitely a bit more ‘give’ which helps to reduce feedback to the bars. The other thing that he noticed is that there’s none of that knocking feeling mid stroke which we’ve so often had on previous 40’s. The ability to dial in the correct pressure and spring rate (nine settings are available) is also a welcome bonus.

Fox reckon they have spent a lot of time getting the negative spring system right (a titanium coil spring) and the result is that they’ve ended up with a very supple and linear first half of the travel and then the progressivity ramps up as you go deeper into the travel. The level of this progressivity can be adjusted internally to one of nine different settings. The nature of the air spring differs from that of the coil spring so much that Fox have also had to rework the RC2 damper. Years ago we all seemed to be crying out for linear springs (and therefore coil), but it seems that now we often want a more progressive feel and to achieve this with a coil spring you have to rely on the damping to mimmic this, but with this air spring Fox reckon that less is actually asked of the damper, and therefore it can be made to perform better. The natural ramping up at the end has also meant that Fox have been able to do away with the hydraulic bottom out control. To reduce friction as much as possible Fox have even given the damper shaft a Kashima coating.

Adjustments on the damping side are as before, i.e. you get externally adjustable high and low speed compression and rebound damping. There are however a couple of other small changes and those are that on the back of the legs just underneath the seals you now get a push button air bleed port to remove any built up pressure within the fork, and Fox have done a slight tweak to the design of the axle pinch bolts. All in all then these forks really do look to be very promising indeed, which should make this year even more interesting in terms of DH forks than we already thought it was going to be…plus these are also 650b compatible thanks to two size specific lowers, so that opens up another door…

DHX RC4 gallery

The other new product which is being launched today is the latest incarnation of the DHX RC4 rear shock. It comes as little surprise to hear that this shock has been designed to work in harmony with the new fork. The main improvements that Fox set out to make though were to improve the damping performance and increase responsiveness and sensitivity.

On the damping side Fox reckon that frames are now tending to be made with more natural progressiveness built into the suspension design, which in tern means that they feel that they can now offer a more linear shock tune. Like the fork damper this means that the shock can be left to concentrate on pure damping work rather than also having to deal with adjusting the progressivity of the suspension. The addition of Air Assist and Air Assist Volume adjusters instead of the ‘Boost Valve’ does allow you to adjust the progressivity of the shock though, much like the fork, it’s just that now the damping is not expected to carry out that work.

The sensitivity of the shock has mainly been increased by reducing the diameter of the shaft from 5/8″ to 1/2″. This reduces friction and it has the added benefit of allowing more room for oil.

Adjust wise, apart from the Air Assist, the shock remains largely as before with externally adjustable high and low speed compression and rebound damping. So, perhaps less of a reworking than the forks, but the changes should be noticeable nonetheless.

And finally, for those that like to see behind the scenes here are some photos of the development of the new fork…


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  1. steve

    All looks great except why dont fox supply white crowns with their white fox 40. They would look awesome if they were white. Surely it wouldn’t cost that much to have different colours!

  2. gabe

    A Fucking Air Bleed Port!!!! And not even just a grub screw but a whole arrangment of buttons,springs,seals etc. What a monumental waste of time. And its on the lowers. If you really MUST add unnecessary weight at least add it to the unsprung end. Im not saying air bleed ports are pointless but a grub screw in the top of the stanchion should be adequate no? I thought they were going to be grease ports between the seals. I thought that was a good idea as this is not an open bath fork. I think them being air bleed valves is a good idea but executed in the worst way possible. Grrrr

    1. Ed

      A grub screw in the top of the stanchion would not have the same effect because the pressure that is being built up (and therefore needs releasing) is in the lower part of the fork which is isolated from the uppers. Also, the reason why Fox have gone for a slightly more complicated button design is because for optimum performance you want to release any pressure as often as possible. Fox seem to be recommending that you do it at the top of every run, and let’s face it that would never happen if you had to unscrew a grub screw each time.

      The performance of a fork can definitely be negatively affected by unwanted internal pressures and so I’m not really sure that these bleed ports can be described as such a waste of time. I mean in reality these ports are incredibly simple compared to a load of the other internals and if you’re going to go to great lengths to make a fork as good as you can then surely it’s crazy to leave out something so simple when it can make a difference. And as for added unsprung weight we really must be talking about tiny amounts and the benefit should more than make up for that.

      1. gabe

        ok having actually spent a bit of time looking i see why the release valve has to be on the lowers, sorry. i blame short lunch breaks.
        i get that pressure build up inside the fork can affect performance badly but what i dont like is the button. as you say, fox have gone to great lengths to make this the best fork possible, but the button seems a bit of a compromise. having spent the best part of 1.5k on a fork it would seem a shame not to get the allen keys out for a couple of seconds while you stand about rubbing your hands together at the top of a run. the button will probably do the job well for a while. maybe get a bit gritty after a winter of gloop. possibly get gritty enough to become hard to operate. possibly enough to stick partially open after a few more years, allowing more air to leak in. its unlikely, but my point is a grub screw would work better, be lighter and be more reliable for longer than a button. the screw wouldnt even need to be fully removed to let out the pressure, just enough to open a release port, cleaning itself in the process. it may be hassle keeping allen keys handy but tbh if you’re riding somewhere with lifts then you probably have a few tools in your pack and if you’re pushing up then you can probably do a few runs before building up much pressure. just let it out every time you stop for a cup of tea :) i know the weight differences in question are tiny, but when redesigning an already good fork from the ground up its lots of tiny savings that add up to a whole 150g total saving.
        I guess id expect a button on a trail fork, alongside a remote lockout, a travel adjust, all those handy little features. The 40 is a dh fork tho, often a race fork. it’s not supposed to be handy, its supposed to go really fast for a few minutes at a time. over and over again. for years.

    2. Ben

      Gabe, I hope fox make you set of 40s with grub screws. Then when you stack it in the mud and one or both of your grub screws is clogged with mud and you can’t bleed your forks, you may think hmmm maybe the team that decided to use buttons were actually engineers. They did not just think oh shit buttons could be cool. They use a design process that probably involves weighing up the pros cons of many possible solutions before they pull the trigger on the design for a new part, especially something as complex as new lowers.

      1. Gabe

        So what you are trying to say is you think a plastic button with some sort of very very small spring, at least one very small seal (held shut by said very very small spring) and some sort of actuator and guide system also very small, and likely to be plastic,will be more impervious to British grime than a grub screw covering a hole. You are welcome to that opinion. I disagree. I hope fox make me a set with grub screws too. Cheers man. When I stack it in the mud and they get clogged ill do what I always do in that situation. Get the next size down Allen key out and give it a bit of a poking. 3 seconds work, job done. When your button gets clogged up I don’t know what you’ll do. Hopefully it’ll be serviceable. At least then you’ll be able to get it cleaned up when you get home. No more riding for you that day tho…. By the way I’m sure the engineers did think long and hard about the design. But sadly performance can’t be their only concern. They also have to consider aesthetics, one-upping the competition, advertisable features etc. I think these buttons are a gimmick.part of the whole tool free craze covering all our bikes in built in knobs and dials that once set hardly ever get used again, adding pointless weight and complication and probably causing things to get knocked out of adjustment more often. These buttons will get used regularily at least. They are probably the best example of tool free gimmickry, but still not as good (and heavier) than a grub screw.

      2. Fergus

        I’m honestly amazed you have so much time to type so much over a f-king button or grub screw. Simmer down Kim Jong Un; its a button.

      3. gabe

        @ Fergus (cos for some reason his comment doesn’t have a reply button) Aww diddums doesn’t like that I’m right so has resorted to name calling. Reminds me of a certain Korean dictator…. Thanks for confirming that I’m right tho.

      4. Fergus

        I still dont get why you’re so adamant you know better than a team of leading engineers with years of experience. Until you’ve tryed it why kick up a fuss? lets be honest though even if it would be better with a grub screw its not going to make you any faster.

      5. Dan

        Fergus is right, chill out. If you want to be an internet engineer head over to pinkbike that’s where they all seem to reside. Dirt imo is where the more mature/down to earth people are and I’d like to keep this way.

      6. Robbie

        Guys, I wouldn’t pay to much attention to Gabe, he was calling hose on disc brakes ‘cables’ the other day…He just comes across as a typical armchair expert, always beating his chest trying to show how knowledgeable he is and getting involved with every post. Pretty boring really

      7. gabe

        Getting bored of this whole thing now. Ive seen alot of name calling, attempted character assasinations, questioning of my knowledge/experience etc. Yet no one has actually managed to put down a convincing reason why im wrong. And saying “someone got payed to design it so they must be right” is not a convincing reason. nor is saying “im too lazy to spend 3 seconds looking after my £1.5k forks” in my opinion. Surely “mature/down to earth” people who disagree with something at least attempt to give some sort of reason why they disagree? I have tried to make my point clear and simple enough to understand. Ed sent a pretty reasonable rebuttal. No one else has. Perhaps I should head over to pinkbike. Don’t have internet at home so I have little experience of either site. I hope its not true that all the people who actually give a shit how something functions are over there. I prefer the dirt site, but if the mature down to earth conversations are over there, i guess thats where I’ll be looking on my lunchbreaks from now on. And yes robbie i did call a hose a cable. I guess 20 years of habit die hard.

  3. jonesdirt

    Any questions please ask, we’ll be taking this fork head to head with the competition in a few weeks

    1. Gorgonzola

      A RaRe air 40 air fce off would be awesome

    2. Craig B

      Handy – I am in the market for some forks. Please deliver report post haste – money ready to be spent.

    3. Hancock

      Any chance of you getting hold of an Avalanche cartridge equipped Boxxer (or 40, 888)? I know in the context of the next few weeks that’s not a go-er, but there needs to be a (professional) comparison between top end off the shelf parts and a Boxxer RC with £250 worth of Ava tuning.

      1. gabe

        I second that. A proper professional review of all the aftermarket shock tuning options (Ava carts, CR1carts, Enduro seals, etc.)would be brilliant. It seems odd to me that aftermarket suspension upgrades are often simply overlooked in the mtb market. except push. for some reason.

    4. Skootur

      You have to make sure its up against a new Dorado (one of the few top-end air forks, and a proven system at that).

      1. alansicmoto

        I second that, a Dorado comparison is definitely needed. Far too often over looked.

  4. Johan

    Feels like the good ol Boxxer is being left behind in the dust by the competion.

    Ssure is a good time to be dh racer at least, carbon frames popping up everywhere and new suspension goodies from new and old players. Now we just need cheap(er) and sturdy carbon wheels and we are set!

    1. Jan

      Why do people presume carbon frames are the be all and end all

      1. Ed

        Well said, there’s definitely still a place for well made aluminium frames.

  5. jonesdirt

    …and let’s not forget there’s still a place for a well priced downhill fork to go with that frame too

  6. loafer

    Well said!!

  7. Tom

    just to clarify….who will this suspension fork be available to?

    1. Paul

      maybe they will pull a rockshox, and only provide to the most elite haha

      1. hans brix

        It’s only available by Royal appointment.

  8. greg

    the nice part with the carbon and air craze is that now superb alu frames and coil units will be sold at fair prizes both new and second hand. Just look at the new prize of the dw equipped Turner DHR.
    No, carbon is not the end all be all – i’m on a makulu and i love it, but at the end of the day, everything else being equal, lighter, stiffer and stronger are hard adjectives to beat 😉
    myself, well, i have no plans to swap my coil bos for air sprung fox any time soon. :)

  9. Kevin

    I have a Turner DHR, with a fairly regular build. 888, atomlab rims, hope hubs, gravity light cranks, XO gears and brakes. It is lighter than new balckbox Demo and carbon Santa Cruz also with Boxxers.
    Aluminium Mondraker is lighter still.

  10. Kevin

    Interesting to see if these work better than Boxxer Airs. I never really liked the old 40s as they were too linear, but looks like they have changed this.

  11. screwball

    650b option!!!

  12. Benzo fury

    Don’t believe the hype. Don’t believe the hype! Hmm, we shall see.

  13. Grifter

    Hmm, plastic internals? I’m not sure i like that for how much these will cost.

  14. sx trail

    Hello Dirt, What’s the precise difference between the new and old RC4. Fox says, the new one has an air assist valve, the old one has a boost valve which helps to prevent bottom-out. Wouldn’t the air assist help with bottom-out too? I’m not trying to be paranoid, but it seems like they just change the name -or they haven’t really taken the time to explain the “on the trail” differences. Any input would be appreciated.

  15. Viv Sweetman

    Dates and prices ?

  16. Dave

    Jones: yes, I have a question for your consideration.
    Not all consumers can replace major components every season, so for a consumer who only has the opportunity to replace forks once in a blue moon, which of the current twin crown offerings coming up in your test does Dirt think would be the most likely to give long term reliability?

    1. Grifter

      Marzocchi 888.

  17. james

    will it blend?

    1. Hancock

      Everything will blend my friend. Everything except Chuck Norris, because Chuck don’t blend.

  18. hairy

    so every 2 months or so when I rebuild my boxxers why is there no gush of air being released due to pressure build up? is the air build up unique to fox 40s?
    why no carbon (at least lower) crown? could work.. also carbon steerer?
    20mm is so last year why not do 22.5mm so we all have to buy new wheels? marketing ploy..


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