2021 Fox 40 Factory
Mounted To: Nicolai G16
Test Duration: 3 months
Test Location: Washington
Travel: 203 mm (190 mm air shaft available aftermarket, tested)
Wheel Sizes: 27.5” & 29”
Available Offset Options:
- 27.5″: 48 mm (44, 52, and 56 mm crowns available aftermarket)
- 29″: 52 mm (44, 48, and 56 mm crowns available aftermarket)
Stanchions: 40 mm
Version Tested: 27.5” wheel; 48 mm offset; 190 mm travel
Stated Weight: 2816 g / 6 lb, 3.3 oz
Blister’s Measured Weight (27.5”, 190 mm travel, uncut steerer tube): 2834 g / 6 lb, 4.0 oz
MSRP: $1749
Intro
The Fox 40 has been a mainstay in the dual-crown fork market since it first appeared in 2005, and for 2021, Fox gave it an overhaul. The namesake 40 mm stanchions remain, but the chassis is all new, and the spring and damper have seen updates as well. So just how different is the new 40 from the version it replaced, and how does the new fork perform in general? Let’s dig in.
The Design
Fox gave the 40 a new chassis for 2021 (and dropped the “49” name for the 29er version — it’s officially the “40” now, regardless of wheel size). Visually, the most obvious change is the new lowers, with their more rounded arch — in keeping with the design language of the new Fox 38, and similarly-redesigned 2021 Fox 36. Fox says that the new arch juts farther forward than the prior version to offer more headtube clearance at bottom-out, particularly in shorter-offset configurations. While I haven’t had any issues with the pre-2021 40 in this regard (including when running it with the offset-reducing Mojo MORC 40 crowns), some modern bikes do have increasingly bulbous headtubes, and working in some more clearance can’t hurt.
The 2021 Fox 40’s new lowers have a few more details in store. Most significantly, Fox has added what they call “lower leg channels,” which are essentially a pair of ribs that run up the backside of each fork leg. The idea is to open up a path for air and bath oil to move past the lower bushing and into the upper portion of the lowers. The oil is meant to lubricate the upper bushing and seals while the displaced air is used to mitigate the pressure buildup that occurs in the lowers during compression.
As with the prior generation, the 2021 Fox 40 has bleed valves on the back of the lowers to relieve with the push of a button any pressure that might build up in the lowers. The 20 mm Boost axle carries over as well, and though Fox is placing renewed emphasis on the floating design (which adjusts to accommodate variances in hub width without pinching the lower legs together and causing binding), the 40 has had this feature since its inception. Unlike Fox’s single-crown offerings, there’s no quick-release axle option. The 40’s axle (reasonably, in my view) remains bolt-on only.
The 2021 Fox 40 also (finally) has a bolt-on fender available. Unfortunately, the fender wasn’t available for our testing, but it attaches via two bolts on the back of the arch, as well as behind the air bleed ports. Fox has had bosses in the back of the arch that look to be intended as fender mounts on many of their forks (including the 40) for a long time now, so it’s great to finally see a compatible fender show up. Unfortunately, the new lower design means that the fender won’t retrofit to pre-2021 forks.
As with the prior-generation fork, the 2021 Fox 40 uses post-mount brake tabs for a 203 mm brake rotor, and rotors up to 230mm-diameter may be used with an adapter. The straight 1.125” steerer tube carries over as well — there’s really no need for a bigger, heavier, tapered steerer tube with a dual crown fork, and the smaller lower bearing leaves more room for reach and angle-adjust headsets and the like.
The 2021 Fox 40 gets new crowns as well, and for the first time on the 40, they’re available with different offsets. We’ll cover the particulars of the offset options in more detail below, but the new crows have a sharper, more angular look, and more offset at the crown than the prior generation. This puts the stanchions a touch farther forward, and thereby tightens the turning radius that can be achieved before they run into the frame. The net reduction in offset for the new fork (again, more on that in a bit) is accomplished by substantially reducing the amount of offset in the lowers.
Air Spring
The overall design of the air spring hasn’t changed substantially in the 2021 40 fork, but the volume of the negative chamber is a touch larger than the outgoing model. The 40 still uses an air spring with an auto-equalizing negative spring, via a machined dimple in the stanchion that allows air to bypass the air pistol seal at topout. Positive-chamber volume, and thereby progression, can be adjusted via volume spacers that clip to the underside of the air top cap. This sort of system will be familiar to anyone who’s spent time with Fox or RockShox’s mid- to high-end forks from the last few years, and it works well — no need to reinvent the wheel here.
Damper
Fox’s Grip2 damper carries over to the 2021 40 fork as well, but with some significant updates. The basics of the layout are similar — it still features adjustable high- and low-speed rebound and high- and low-speed compression, and uses a spring-backed internal floating piston (IFP) to manage displaced oil — but the internal valving has been revised.
Most notably, the Variable Valve Control (VVC) design, which was previously used on the high-speed rebound circuit only, has been applied to the high-speed compression one as well. In short, the idea is to have the high-speed adjuster fundamentally change the stiffness of the valving, rather than simply applying preload to the valves. Adding preload to a spring (the valves in a damper are a type of spring) increases the force needed to get the spring to start to compress, but doesn’t change the spring rate / stiffness deeper in the stroke.
VVC achieves this by turning a winged valve on top of a spiral ridge that supports it. When the ridge supports the wings at their tips, the leverage on the valve is increased, effectively making the valving lighter. Supporting the wing closer to the middle decreases the leverage and makes the valving stiffer. You can see the ridge (indicated by the pen tip) and one side of the wing (the shiny silver tab) in the screengrab from Fox’s video explaining VVC below.
The full video is on Youtube (Search “Dialed S2-EP5”) with the real action starting at the 2:57 mark. [Jordi happens to be dissecting a 38 damper here, but the new 40 uses the same design.]
Put more simply, the idea is to increase the usable range of damping adjustment without needing to take the fork apart and change the valving. I’ll go into more detail in the on-trail impressions below, but in large part, Fox’s efforts have paid off. It’s a clever system.
Offset
[If a reminder of what fork offset is and how it impacts bike handling would be helpful, check out our Fork Offset 101 article.]
Until now, the 40 was only offered with a single offset option for a given wheel size. That changes for 2021. Fox is now offering crowns with four different offsets for the 40, ranging from 44 to 56 mm, in 4 mm increments. Additionally, both flat and drop upper-crowns are available, to accommodate a range of headtube lengths. Aftermarket versions of the fork ship with the 48mm-offset flat crowns for the 27.5” version, and 52mm-offset drop crowns for the 29er. The other variants are available separately, and OE buyers (i.e., frame manufacturers speccing the 40 on their bike builds) can opt for a non-standard version if desired.
The prior version of the 40 used the same crowns for all wheel sizes (flat and drop-top crowns were both available) and varied the offset between wheel sizes by changing the offset at the lowers. The 26” fork (which was dropped from the lineup a couple of years ago) came with 45 mm of offset, the 27.5” version had 52 mm offset, and the 29” came with a massive 58 mm.
As I wrote about in the Fork Offset 101 piece linked above, I always found those figures to be too high for a downhill fork — and evidently, a number of Fox’s athletes agreed, as evidenced by the proliferation of the Mojo MORC 40 offset-reducing crowns on the World Cup circuit a couple of years ago.
Fox clearly heard the message, and offering four different (mostly shorter) offsets is a big step forward. I do wish that the range was shifted just a bit shorter for the 27.5” fork though — bear in mind that the offset range is the same for both wheel sizes, but (as laid out in our Fork Offset 101), it does make sense to go a bit longer on the offset for larger wheel sizes, which Fox does do on all of their single-crown forks.
On The Trail
Have all these changes added up to a wildly changed on-trail feel? For the most part, no, but I’m not complaining. The prior 40 was already an excellent fork, and the tweaks that Fox made are generally for the better — they’re just subtle.
To be honest, I can’t really tell any difference in stiffness between the prior chassis and the 2021 version. Fox says the 2021 40 is stiffer than ever, and that’s very likely true. But at some point, being a little stiffer than an already extremely stiff fork is … still just very stout. That said, I don’t find the 2021 40 to be too stiff either. I’m not a huge guy, at 165 lb / 74.8 kg, but I can’t say that I’ve ever felt like any version of the 40 was suffering from being too stiff, and consequently notably harsh. To me, it just feels precise. The front wheel goes where I point it without complaint or drama.
Where the 2021 40 does feel like a notable improvement over the prior versions is in terms of small-bump sensitivity. The difference isn’t night-and-day by any stretch, but the new fork is just a bit smoother to break free and start moving, and feels a touch more supple early in the stroke. The larger negative air chamber likely deserves the bulk of the credit here, but Fox has also done a good job of making the whole system move smoothly and with relatively little friction as well.
As Noah Bodman noted in his review of the Fox 38, the on-trail experience of the new Grip2 damper with VVC applied to the high-speed compression circuit isn’t wildly different from the prior version (and to reiterate, the 2021 40’s damper shares its basic design with that of the 38, just reconfigured for the larger chassis). The most significant difference that Noah felt was that, while it was difficult to make the revised VVC Grip2 damper feel unduly harsh, it did seem that the overall range of high-speed compression adjustment, in particular, had narrowed a bit from the prior version. I’ve spent some time on the 38 as well, and fully agree with Noah’s take. On that fork, I found myself running the HSC surprisingly firm (in terms of the adjuster’s overall range — it doesn’t feel as if that produces an especially high amount of damping).
The same is generally true for the new 40, but the high-speed compression tune does feel a touch firmer. It’s still relatively light overall and heavier, more aggressive riders might be left wanting for more high-speed compression damping without a bit of work to re-valve the high-speed compression circuit. At 165 lb / 74.8 kg, I’m not particularly looking for more high-speed compression than the new 40 has on offer, but I am running it at or near fully closed, depending on the trail and conditions.
While the new damper doesn’t have as wide a range of high-speed compression adjustment as the old one, it does feel notably less spiky with the HSC adjuster turned up considerably. Remember what I said before about preloading a spring — in most forks, cranking up the high-speed compression adjuster preloads the valve, which increases the force needed to get it to open in the first place, but has less effect when going from partially to fully open. I think the addition of VVC to the high-speed compression circuit is overall going to be an improvement for most riders, but folks looking for a very firm HSC tune are likely going to be left wanting a re-valve. But, of course, those same people would likely be better served by re-valving the prior generation (or most other) forks as well, instead of cranking the adjusters and dealing with the compromises that entail.
As I alluded to before, the reduced-offset options on the 2021 40 are a big step in the right direction, but I wish that the 27.5” fork (which I’ve been using) got some even shorter options. The shortest offset available, 44 mm, is about as low as I can imagine wanting on the 29” fork, but my preference would be to go shorter still for 27.5” wheels. Bear in mind that 44 mm is the long offset option for the 27.5”-wheeled Fox 36 and 38.
Unfortunately, the 44mm-offset crowns weren’t available for our testing, but I was still able to experiment with going shorter than the stock 48 mm, first by using a set of crowns off the prior-generation fork (which nets 41 mm total offset) and then also by using the Mojo MORC 40 crowns that I mentioned earlier, which produce either 38 or 33 mm of offset, depending on which position they’re run in. I’ll grant that 33 mm of offset is ridiculous. With that little offset, the steering becomes floppy, and straightening the bars back out on the exit of a corner becomes a chore.
I don’t have a clear preference between running the Fox 40 at 38 or 41 mm of offset, but that’s more in the range I’d like to be in, and unquestionably find an offset figure in that ballpark to be an improvement over the stock 48 mm option. Running the offset significantly shorter than the stock 48 mm calms the steering down considerably at speed, and makes the bike feel more stable without feeling unduly sluggish. For a fork that’s specifically meant to be run on very long, very slack bikes that are predominantly focused on going downhill very quickly, I strongly feel that a relatively short offset feels more in keeping with the handling characteristics of these sorts of bikes.
[And again, our Fork Offset 101 article goes into much greater depth on the subject if you’re curious about more specifics.]
I wish Fox had taken an approach a bit more similar to what RockShox does with the Boxxer — their competitor to the 40 — which comes in 36 and 46 mm offset for the 27.5” fork, and 46 and 56 mm for the 29er. This is accomplished with just two total sets of crowns. The 29er lowers have 10 mm more offset than the 27.5” ones, and thus the same “short” and “long” offset crowns produce different offsets for the different wheel sizes. It’s great that Fox decided to offer four different crowns for those inclined to experiment with offset, but the range of offsets that they provide would be more usable on the 27.5” fork if it were shifted shorter. Increasing the offset in the 29” fork’s lowers (which are already a separate part anyway) and then shortening the crown offsets to match would keep the same offset range for the 29er fork, while shortening the 27.5” one into what I would consider a more usable range. I find it very hard to imagine that anyone wants a 56mm-offset 27.5” DH fork, but I’d certainly welcome shorter than 44 mm myself.
Apart from the greater offset than I’d prefer though, the new 40 is an excellent fork. While the changes Fox has applied to the 2021 model don’t hugely change the on-trail performance compared to the prior model, a number of refinements have proven to be subtle improvements, and the end product is impressive.
Fox 40 vs. Burly Single-Crown Forks (Fox 38 & Rockshox ZEB)
As an aside, I’ve been running the 40 on my Nicolai G16, which, rather than being a dedicated DH bike, is a bike that I pedal to the tops of climbs with some regularity. Given that, I wanted to include a quick note on dual-crown forks, in general, for that kind of use. I’ve had various iterations of the 40 on that bike for several years now, and have also spent considerable time on most of the major options for burly single-crown forks, including Fox’s 38.
In short, the only downside of any particular note — provided that your Enduro bike is rated for a dual-crown, as many are not — is weight. A Fox 40 weighs right around 400 grams more than a Fox 38. That’s not insignificant, but it’s not unbearably massive either. Even a relatively small water bottle, when full, is around 600 grams, for reference. And while the latest crop of long-travel single-crown forks (most notably the Fox 38 and RockShox Zeb) are indeed significantly stiffer than the models of old, they’re still no match for a 40 in that regard. That added stiffness of the 40 pays off in terms of precision in steering and holding a line, and when it comes to keeping the fork from binding and twisting as it compresses, due to flex in the chassis. If your riding mostly entails long, grinding climbs to get to steep, sustained descents, a dual-crown fork is absolutely going to perform better on the way back down, and it just becomes a matter of what you’re willing to drag to the top in the first place.
To be clear, I still don’t think that most people should be bolting dual-crown forks to their Enduro bikes, but I also don’t think that it‘s a crazy proposition for everyone, and if you can live with the weight penalty and have a bike that can handle it, it’s worth thinking about.
The Bottom Line
With their new 40 fork, Fox took an already very good fork in the prior-generation 40 and tweaked it for the better for 2021. The chassis is superbly stiff, smooth, and low friction, small-bump sensitivity has been improved, and my biggest gripe about the old model — the excessive offset — has been at least partially addressed. I only wish Fox had gone shorter yet on the offset options, particularly with the 27.5” fork, and heavier and / or very aggressive riders might find themselves wanting a bit firmer of a high-speed compression tune. The changes Fox made are a solid step forward, though, and the resulting product is excellent, just not quite perfect.
I read you use this fork on a G16…
I have a G16 and am planning to install a fox 49.
I want to decrease travel to 170.
Did you decrease travel or use the full 203mm?
As mentioned in the review, I ran it at 190mm using the air shaft that Fox offers for that configuration. There’s not an easy way to get a 40 lower than that without custom parts.