Travel: 203 mm
Wheel size: 27.5”
Stanchions: 40 mm
Axle to crown: 594 mm
Offset: 52 mm
Weight : 2735g
Reviewer: 5’9” 155lbs
Duration of Test: About 4 months
Locations Tested: Montana, Idaho, British Columbia
The Fox 40 needs no introduction – it’s been the winningest fork on the DH World Cup circuit for quite a few years running. In 2016, the winner of all but one race was riding a 40, and notably, Rachel Atherton took a clean sweep of the season aboard a 40 in the women’s class. There is absolutely no question that the 40 has the chops to win races.
So going into this review, I knew that the 40 was a great fork, but I was more interested to see how I got along with it at a non World Cup pace. Because let’s be honest, not many of us are pushing any of our equipment to the limits that Gwin, Hart, or Atherton are.
The 40 is available for both 26” and 27.5” wheels, and is built around the fork’s namesake 40 mm stanchions. The 40 is only available as a “Factory” level fork, meaning that every 40 has Kashima coated legs, a FIT damper, and the Float air spring.
The crowns and lowers on the 40 are forged and then relieved of excess material to save weight. Fox didn’t go overboard in whittling away metal though, which keeps the fork plenty stiff. The Kashima coated stanchions are also straight throughout their length; they don’t have a relieved portion between the crowns like the BOS Idylle or Marzocchi 380 forks. This makes the 40 more adaptable to different frames – I’ve run into issues fitting the Idylle to bikes with short headtubes.
The wheel is attached with a standard, bolt on 20 mm axle. The fittings are replaceable, so if you strip one or cross thread it, you’ve only made a $5 mistake, not a $200+ one. While the 40’s bolt on axle isn’t quite as quick as Rockshox’s Maxle Lite DH that comes on the Boxxer, I prefer the axle on the 40 – it’s more secure, and there’s less to go wrong with it.
The 40’s air spring, housed in the left leg, shares its basic design with the Fox 34 and 36 forks. A bypass port at the top of the fork’s travel automatically equalizes the negative air chamber, which makes for a supple initial stroke and prevents the fork from topping out.
The large volume of the 40’s air chamber makes for an impressively linear stroke, which can be tuned with volume reducers that attach the the underside of the top cap. Despite its linear nature, with maximum volume reducers (7) installed the 40 becomes quite progressive. The most I ever ran was 5 in whistler, where I was looking for better bottom out resistance. It’s also worth noting that the 40 runs on relatively low pressure, which helps minimize stiction associated with tight seals.
The 40’s FIT damper offers rebound as well as high and low speed compression adjustments. Both compression adjustments are found on top of the fork’s right leg, with the rebound knob at the bottom of the leg. The rebound knob is protected by a cap, which keeps it from getting gummed up with dirt, and also protects it in a crash.
The FIT damper is based around a bladder system, which keeps the oil contained within the unit. As the fork compresses, oil is displaced and needs somewhere to go. Some forks handle this with an open bath; the oil is just sloshing around inside the fork, and there’s plenty of room in there for oil displacement. Other forks use a floating piston that can move out of the way as oil is displaced.
The 40 handles that displacement with a bladder that can expand. When the fork is fully extended, the FIT bladder is “deflated.” As the fork compresses and oil is displaced, it fills the bladder like a balloon. This bladder system is generally similar to that used in Rockshox’s Charger damper.
The FIT bladder damper has a number of advantages over open bath or floating piston systems. The bladder system minimizes the total oil volume in the system (which saves weight), it keeps the oil contained within the damper unit (which keeps the oil cleaner), and it keeps the oil away from air (which minimizes cavitation). All of those things are designed to produce a better fork with more consistent damping characteristics.
Right out of the box, the 40 feels smooth and controlled. While the fork broke in a bit over the next few rides, it felt like a nicely finished, race ready product right from the get go.
In fussing around with the fork’s settings and adjustments, it became clear pretty quickly that the 40 is very adjustable. Between the basic compression settings, the air pressure, and the air volume adjustments, it’s pretty quick and easy to dramatically alter how the fork rides.
Of course, the 40 isn’t unique in having those adjustments – a few other forks have separate high and low speed compression adjustments as well as air chamber adjustments. But I was pretty impressed how easily and how significantly I could change the fork’s behavior. Without wading into changing oil weights or messing around inside the damper, I could tune the fork for completely different situations in under 5 minutes.
As an example, my first week or so on the fork was at Whistler, and I tend to prefer a much stiffer fork that can handle the hard hits that Whistler tends to dish out. So in Whistler, I ran the fork relatively stiff with a lot of volume reducers to handle big hits without bottoming out harshly. But back at the local bike park in Whitefish where the trails are a bit flatter and less technical, I softened the fork up, took out some volume reducers, and mostly used the high speed compression adjustment to address bigger hits. It’s a night and day difference in how the fork rides, and it was easy as pie to make the changes.
Interestingly, regardless of how I set up the compression settings on the 40, I found that the fork worked best for me with the rebound set a little slower than I would on most other forks. Slowing down the rebound helped the fork feel a bit more planted, but it still didn’t seem prone to packing up.
Aside from the ease of adjustability, the defining characteristic of the 40 is really that the chassis is very, very stiff. I’m completely comfortable calling it the stiffest DH fork on the market.
Fork stiffness is something of a debate – pretty much everyone agrees that fore-aft stiffness is good, but plenty of people argue that a bit of torsional flex is actually a good thing. The argument is essentially that a reasonable amount of torsional flex allows the front wheel to track around obstacles rather than being deflected by them. The flipside of that argument is essentially that extra torsional flex makes the bike’s steering a bit less precise.
Having ridden both flexier forks and stiffer forks, my take is really that both have their benefits in certain situations. More importantly, I find that on any given trail, I’ll find situations where a stiff fork is preferable, and other situations where I think a bit more flex would be beneficial.
Due to its stiffness, the 40 is a very precise fork – it goes exactly where you point it. This is great at higher speeds, but it’s also noticeably easier to force the fork through slower technical sections – it never gets flexed off line by an errant root or rock. On the other hand, there were a few rocky minefields where I did feel like I’d get bounced off rocks that a flexier fork might have just wiggled past. On the whole, I prefer a stiffer fork to a flexier one – the situations where a stiff fork is beneficial seem to outweigh the situations where it isn’t, but I can also see how other riders might come to a different conclusion.
It’s also worth noting that, at least with upright forks, torsional stiffness and fore-aft stiffness tend to go hand in hand, and the 40’s stiffness is clearly a benefit when it comes to smashing into bumps straight on. The fork doesn’t flex much, which means the fork’s movement isn’t inhibited by flex-induced friction in the bushings. It also means that the fork retains its composure while bashing through hub-deep holes while on the brakes. In those situations, the suspension works like it’s supposed to, whereas some flexier forks noticeably bind up and become a lot less smooth.
The point of any suspension fork is really to absorb bumps and help the front wheel maintain traction, and in that regard, the 40 does exactly what it needs to. Some forks, like the Bos Idylle feel extremely active – they use their travel very easily. In terms of smoothing out the trail, this is great, but they give up a little ground in terms of support. An extremely active fork like the Bos is a bit less composed in hard compressions and corners.
To put it another way, some forks use most of their travel, most of the time. The 40, on the other hand, uses no more of its travel than is absolutely necessary. Even with the fork set up relatively soft and without a lot of compression damping, it still feels like the 40 is very judicious in its use of travel.
That trait, combined with the 40’s stiffness makes the fork a bit less comfortable – particularly early in the season when my hands and forearms aren’t quite in shape, the 40 takes more of a toll on my body. But that reduction in comfort comes with a significant gain in the bike’s composure – the 40 never feels wallowy or mushy – it just feels like it wants to go fast.
NEXT: Maintenance and Durability, Comparisons, Etc.