2021 is the year that Fox opened the floodgates and let their engineers go wild. We see more changes in the product line-up than I’ve ever seen in a single launch, and none of them are superfluous. Almost everything has been altered, and in big ways. From the X2 to the DHX2, every part of everything has been assessed, scrutinized, and fully revised. But most exciting, in my mind, are Fox’s forks. Many of these changes span all the more gravity oriented forks (34, 36, 38, and 40), but we are going to focus on our long time favorite, the 36, and the new kid on the block, the Enduro specific, long travel 38. The changes described below apply to both of these forks, and make them into what are likely the most advanced telescopic forks in the world.
There are always small differences in tolerances with different hubs - some are a hair wider than the 110mm BOOST spacing, some a hair narrower. In the past, we’ve just shoved the hub in the fork (or if it was smaller, let it drop right in) and clamped it down. This works, but it either pushes the lower legs apart or pulls them together, which creates binding as your fork stanchions try and move smoothly through now-slightly-bowed lower legs.
With the new 36 and 38 there is a small cylinder - a “floating” sleeve - through which the quick-release axle goes on the drive side of the fork. It can move in or out, towards the hub or away, so as to add or remove space as needed for your specific hub. Now, the lower legs and upper stanchions are in perfect alignment for smooth sliding - at least until we go smashing down our favorite rock garden, but Fox has more in store to help with that!
Lower Leg Channels & Air Bleeders
There is a limited amount of space inside your fork. Aside from the air spring (a closed chamber that is designed to be compressed and then to forcibly expand) the rest of the space inside your fork is also a chamber that, as your fork pushes into its travel, has a quantity of air in it that squishes and wants to un-squish. This is unavoidable, but not actually intended. This secondary, unintentional air spring can sometimes have enough of an effect to keep you from using all the travel in your fork, and since it’s not user controlled by you and your shock pump, it can change depending on things like temperature and elevation.
By opening up more space in the fork for this air to move (essentially increasing the total available volume, like removing a band in your shock), the new 36 and 38 go a long way in removing this as a problem. On top of that, the new channels help get oil up to the dust wipers and seals, keeping everything nicely lubricated and running smoothly.
A secondary method of mitigating the unintended effects of having a closed air system inside the fork is by adding external bleeder valves. All one has to do is press these little buttons on your fork lowers to release any compressed air that has built up in your fork.
Increased Structural Stiffness
With the advent of Enduro racing, riding demands that used to be relegated to bikes that could weigh 40 to 50 pounds were placed on bicycles that need to be pedalled all day. To meet this requirement, engineers have been pulling out all the stops to make bikes stiff, strong, AND light. One way to do this is by using larger diameter tubing. It lets you get similar stiffness and strength out of tubes with thinner walls, so it weighs less. Or, in the case of the new Fox 38, more strength out of similar weights.
Another place this strategy has been employed is the diameter of the frame tubes. In question here are the bicycles head-tube (that’s the one the fork’s steerer goes through, right under your stem). To allow for larger diameter head-tubes, the new Fox 36 and 38 forks have moved the fork arch further out front, away from the stanchions. This future proofs your fork for any hair brained frame engineers that decide to push the limits of tube diameters. The new arch shape on these two forks is also designed to make the fork itself stiffer. Win, win, WIN.
Lastly, with the Fox 38, Fox has introduced a new steer-tube (the part of your fork that your stem latches on to) that has more material on the insides - but only where it’s needed. Most of the impacts that forks encounter come from directly ahead, so the 38 has thicker front and aft steer-tube walls to increase strength and stiffness in that direction. This material is all added to the inside of the tube, so there is no need to get a new headset or anything like that.
Tuning on the 34, 36, and 38
When Fox replaced the RC2 damper (rebound, and two compression adjustments) with the Grip2, they not only changed the way the whole damper was set up, but they also broke the rebound adjustment into two parts - high-speed and low-speed rebound adjustment. The high-speed rebound adjustment comes into play when your fork is more fully compressed, and the air spring is trying to push it back out with a lot of force - generating higher rebound (de-compression) speeds. The low-speed rebound adjustment comes into play the rest of the time - when your fork is only slightly compressed and wants to extend, but there isn’t a full 6 inches of “spring pressure” behind it.
Not only did they create this extra adjustment, but they changed how the more important of the two (high-speed rebound) was accomplished. To try and explain that, let me quickly run through damping and what it does.
Damping is what keeps your fork from acting like a pogo stick. It turns an uncontrolled spring into something that can keep your wheel on the ground and give you traction. Damping works by changing the speed at which oil can flow through a tube. To contract (fork compression) and expand (fork rebound) the spring in the left leg of your fork, it also has to push (again, compression) and then pull (rebound) oil through a tube in the right leg of your fork. The little red (rebound) and blue (compression) adjusters have historically changed how much pressure is applied to one-way valves that oil flows through. These are called shims, and they are just very thin little metal washers that cover up holes (ports), creating the one way valve. The oil gets pushed through the hole, hits this shim, bends the shim away, and moves happily along its way. If the shim has more pressure behind it (more clicks on your knob) then it is harder for the oil to push it open. Fewer clicks, easier and faster movement.
But that design has some limitations. Putting pressure on those shims isn’t the ideal solution. It doesn’t make for the smoothest range of adjustability, and runs into limitations for different people pretty quickly. For a light person, ideally you would open up your fork and replace the stock shim with a thinner one, which the oil would have an easier time pushing away. Adding less pressure to the one that’s in there via fewer clicks on your knob only goes so far.
With the original Grip2 damper, Fox created a way to do this via clicks on the knob (at first only for high speed rebound). No more opening the fork to get the rebound set up perfectly. With the 2021 Grip2 damper, they’ve added this technology, called Variable Valve Control (VVC) to the high speed compression valve also.
What is VVC, and how does it differ from the previous design? Because the tech diagrams get a little confusing (these are teeny tiny little parts) I’m going to use an analogy. Imagine walking through a door. Regular door. Say it’s your bathroom door. You are the oil. The door is the shim. Your annoying kid brother that has been in the bathroom all morning and won’t let you in is the old adjustment knob.
With the old design, adding damping (more clicks on the knob) was the equivalent of your kid brother pushing harder on the back of the door, in an attempt to not let you, the oil, in. If you’re a massive football player, you’ll blow the door open no problem - “get outta here, you’ve been picking at zits for an hour!”
If you’re the younger sibling though, and weigh half as much as your brother, you might never get the door open, even if your kid brother isn’t even there. The door itself might be too heavy, and you’d have to take your whole fork apart to replace the door (shim) with a lighter one.
With the VVC, Fox is working smarter, not harder. Now when you remove clicks on your knob, instead of changing how hard the kid brother is pushing on the door, they’re changing where on the door you (the oil) are pressing. Less clicks (less damping), and you’re pushing right next to the door knob. More clicks, and your pushing on your door closer to the hinges. You’re changing how much leverage the oil has on the door. So now, even if you are a teeny tiny toddler, you can move far enough away from the hinges to get enough leverage to get it open. And if you’re a football player, you’re trying to open the door by pushing on it from right next to the hinges, where you have almost no leverage. No more replacing the door.
This isn’t a perfect analogy, but it gets to the root of what Fox has done with VVC. Suffice it to say it’s a very cleverly, tidy design, and it offers more suitable solutions for more riders.