Earlier this year we saw Fox and RockShox two new fork offerings in the form of the 38 and the Zeb. Both these offerings sit at the top of the travel tree for single crowns, with only the double crown 40 and Boxxer having more travel. Both are aimed at full on enduro racing and heavy hitting riding, and combined with their long travel stats there have been some changes needed, compared to the 36 and Lyrik, to cope with these demands. Both share the same stanchion diameter of 38mm and have travel options up at 180mm in the case of the 38, and a whopping 190mm for the Zeb, which for that lonely single crown is a hell of a lot.
With so many similarities in terms of dimensions, intentions and release timing, it was only fitting that we put them head to head to see how each one performs, and if there’s one that sticks its large diameter head in front of the other. This is the Fox 38 versus the RockShox Zeb.
Fox’s naming is pretty easy to follow, with the 38 referring to the diameter of the stanchions and this being the most noticeable change to the new fork. Slightly more hidden away, though, is an oval butted steerer tube, designed to place more material at the front and back of the tube to help boost the stiffness under hard riding.
There’s a return of the floating axle, something that the 40 always had and older 36s too.
Fox 38 DetailsWheel Sizes:
27.5" & 29"Travel:
150mm - 180mmOffset:
37mm or 44mm (27.5"), 44mm or 51mm (29")Weight:
2458g (29" / Factory / 170mm / 44mm / Uncut Steerer / QR axle / 1 token)Price:
$949 - $1199 USDMore info: ridefox.com
With either the QR axle or bolt in Kabolt, the hub is clamped against the brake side lower leg, leaving the other leg free to float on the axle via a tube spacer to find its perfect alignment. The idea is that a fork's friction shouldn’t be at the mercy of hub tolerances, and allowing the fork legs to be correctly aligned gives them the path of least resistance when in use.
The Factory 38 we had for test came with the QR axle, which along with the tube spacer that it needs weighs 123g. If you choose the 46g Kabolt option, then you can drop the fork weight down to 2,381g, still with one token and an uncut steerer.
Fox also incorporated bleed valves on the back of the lowers to purge any built up air either through big changes in elevation or air ingress through riding. They also double up as two of the mount points for the Fox mudguard.
The lowers also have moulded in channels to give the lower leg oil a chance to recirculate up to the foam ring, sitting just under the wiper seals, and lubricate the seals and bushings.
With the onset of larger head tubes, either through design choices or the 1.8” lower headset standard, Fox offset the arch forwards to ensure it would clear the frame at full travel no matter the bike it’s fitted to. The 38 uses a 180mm post mount for the brake, with the option to go all the way up to 230mm rotors by using adapters.
Fork dimensions are easily available through the Fox Tech Help page
on their website. But compared to the same travel 36 from 2021 you’re looking at a 3mm longer axle to crown. And compared to a 2020 36 it’s 7mm longer.
The air spring of the 38 is a bit different to the rest of Fox’s single crown forks, with it using an inner tube inside the fork stanchion, which then uses a smaller diameter piston than the 38mm diameter leg would suggest. This changes the compression and expansion ratios while also increasing the air volume that the lower legs take up, reducing their ramp up effect in the fork’s overall performance.
The air spring is tunable with snap-in volume spacers with the maximum number varying on the travel of the fork, with shorter travel versions recommending more spacers to help the air spring ramp with the reduced travel. Max fork pressure is 140psi.
The 38 uses Fox’s latest damper unit, called Grip 2. It offers high and low speed adjustment for both the compression and rebound.
It also uses the newly designed adjusters to change the high-speed compression and rebound, dubbed VVC or Variable Valve Control. They use small propeller shaped plates that when turned via the adjuster adjust the fulcrum, or pivot point, changing the mechanical leverage and effectively stiffening up the entire shim stack or valve behind it. The system uses 7 clicks of adjustment to match Fox’s new generation shocks with the same system.
Low speed damping adjustments use a needle and orifice style arrangement to meter the oil flow through the valve and control the low speed compression and rebound.
The 38’s damper is somewhat open bath, circulating damping fluid through the damper and into the lowers, meaning that the two systems use the same oil for lubrication and damping. This negates any problems with a sealed damper possibly ingesting the bath oil, becoming plump and affecting the fork performance. It also means the lowers on the damper side are lubricated by a lot more oil.
The name Zeb comes from the explorer Zebulon Pike, who is famous around the Colorado Springs area where RockShox has their headquarters. But it too has 38mm diameter stanchions.
RockShox uses a Torque End Cap fitment for the hubs. While the hub width remains the same, the end cap surface contact is upped considerably to help with overall fork stiffness. Although you need to use the end caps to get this benefit. Without and you have to wiggle the hub around a bit to line the axle up.
RockShox Zeb DetailsWheel Sizes:
27.5" & 29"Travel:
150mm - 190mmOffset:
38mm or 44mm (27.5"), 44mm or 51mm (29")Weight:
2274g (29" / Ultimate / 180mm / 44mm / Uncut Steerer)Price:
$699 - $999 USDMore info: sram.com/rockshox
The Zeb uses a simpler bolt on axle with no floating system, although every set of RockShox forks I’ve had need you to splay the legs apart ever so slightly to get the hub to slide in, leaving me wondering if this is their method of mitigating a narrow hub width tolerance.
The Zeb also offsets the arch, to clear the large head tubes and uses a 200mm post mount for the brake. Even though the Zeb can go as low as 150mm, it’s a bit more fitting to see the minimum rotor size as 200mm given the fork's stout intentions. Max rotor size is 220mm. There’s also a bolt-on fender available for the Zeb.
Compared to the same travel Lyrik from 2021 the Zeb has a 5mm longer axle to crown. And compared to a 2020 Lyrik it’s 4mm longer.
The Zeb uses a similar air spring design to the other RockShox forks, dubbed DebonAir, but again the system found in the Zeb is unique to it due to the piston diameter for the increased stanchion and a different negative volume defining part to adjust the positive to negative chamber ratio.
The air spring is also tunable with spacers, but on the Zeb, they screw in with the aid of an 8mm hex tool. There’s even a dual position air spring version available, allowing a quick change in fork travel on the fly. Max air pressure is 148psi.
The Zeb uses the Charger 2.1 sealed damper cartridge with adjustments for low speed rebound and high and low-speed compression.
Low speed adjustments use the same needle and orifice metering system with the high-speed compression adjuster preloading the compression shim stack with 4 clicks of adjustment.
RockShox say they worked to bring the new Charger 2.1 damper adjustment window more aligned with what was needed in the real world, allowing people to potentially use the extremes of the clicks rather than have an extreme that would never be used by the public and racers alike.
The 38 requires a few extra setup steps, coming from the floating axle. But once done it’s set for that hub width when using the QR axle. The Kabolt uses the pinch bolt each time you need to take the wheel in and out and forgoes the tube spacer.
Recommended settings are printed on the side of the fork outputting air pressure and rebound clicks for various rider weight ranges. At 75kg all kitted up, it suggested 93psi with 6 clicks of low speed rebound and 5 of high speed. All clicks being measured from fully closed with the first click you encounter coming back being counted as 1. The fork came with 1 volume spacer installed.
RockShox also prints the recommended pressures on the side of the fork. But their sag markings printed on the stanchions make initial setup a doddle.
They also have the online TrailHead setup tool
, either on the website or via the app. Inputting the fork serial number on the back of the crown gives you access to fork information and documents, setup guides based on your weight and type of bike plus all applicable service and upgrade kits for that fork.
The fork sticker suggested 62psi while the TrailHead app suggested a slightly softer 59psi setup both with 9 clicks of rebound from fully closed. The fork came with 0 volume spacers installed and also suggested keeping it at that.
I’ve been out testing both forks for the past six months in terrain ranging from the demanding steeps of Champéry, Switzerland to the fast root filled forests of Reschen, Italy with everything in between being thrown the forks way. While two bikes were used for filming, my RAAW Madonna served as the test bike for the vast majority of the test period.
Out of the box the 38 took a few more times around the houses to get to a happy window, with it needing much more pressure than recommended, up at 105psi, some 12psi higher than the suggested settings. That up in pressure also needed a change to the rebound damping clicks to keep the bigger spring in check.
The Zeb ended up the closest to the recommended settings with me finding that happy window pretty quickly from those recommended settings.
Both forks exhibit fantastic sensitivity and have maintained that throughout a whole summer and autumn season of riding, although I might be in trouble for not servicing them earlier.
The Zeb feels like butter over small hits and chatter and left me removing it from my list of things to think about as I rode. The 38 matches this, but there’s a touch more information coming through to your hands. Not in a bad way, and definitely not harshness, just a gnat’s whisker more feeling than the Zeb.
When those hits get bigger and the going gets rougher is where the forks become more separated in feel. The 38 gives the impression of riding lower in its travel, almost like you’re missing a spacer from under your stem, whereas the Zeb keeps a higher ride height.
On the flip side, though, in these rough sections of trail is where the 38 then offers more composure than the Zeb, with it being efficient in its usage of travel with the repeated bigger impacts. The Zeb gives the feeling of more movement through the travel, which then needs a bit more body language from your arms to keep up with it.
I tried more pressure in the 38, up at 110 and 115psi, to try and help it ride higher. But was met with an increase in overall harshness even when reducing the amount of compression to account for the bigger spring. I also tried more compression with the same spring rate, but again the harshness increased and I found myself coming back again, eventually settling at 3 tokens and 5 HSR, 8 LSR , 3 HSC and 10 LSC.
With the Zeb I tried more tokens in the fork as an experiment but came back to the stock setting of zero, finding it to be the best balance of travel usage without hitting a wall of progression in the air spring. I eventually settled at 70psi in the air spring, which calmed the fork’s movement through its travel without bringing too much overall harshness into the equation.
I settled at 9 R, 9 LSC and 2 HSC on the Zeb giving me usable options in damping either way depending on the terrain or how hard I wanted to ride. When in that happy window I could ride hard and happy with the fork but just had to have the knowledge of more arm movement in the really rough sections of trail to help with the fork's character. For anyone with a Boxxer they might know the feeling, although with the Zeb that character trait is far less pronounced.
In steep trails, which are in abundance round this part of the Alps, both forks ride well and neither dives drastically while in the steeps or while grabbing a bunch of brakes from thinking you’re ten men and letting off for a touch too long. That is, though, with the 38 needing a higher bar height than the Zeb. But once the bar height is good then the fork does offer good support even though it might be riding lower in its travel.
I can appreciate some people will run the 38 with 180mm rotors, but given the intentions it is a little fiddly to have to use adapters on the brake mount. The Zeb is just a bolt on and go.
Another small point is that our 38 ended up having more than 7 clicks of adjustment, up at 9. With taking apart some of the rear shocks using the same VVC design it could actually be a dead click when you go from one turning direction to the opposite.
Fox 38 Final Settings
Volume Spacers: 3
RockShox Zeb Final Settings
Volume Spacers: 0
Fox recommends service intervals every 125 hours of use or yearly, whichever comes first. But if you ride in extreme conditions or give the fork some extreme use then the service interval is sooner.
There's a 4-digit code on the back of the fork leg than when entered on the tech page
of the Fox website gives you all the service information, specifications and part drawing data.
It's a familiar scenario when working on the 38 to do a lower leg service when compared to the 36 or older Fox forks. Air spring swaps to change travel may be a bit different as you remove the entire inner tube, but it's no worse than a normal air spring swap. The 38 needs 40ml of the Fox 5wt Teflon infused oil in the damper lower leg and 20ml Fox 20wt Gold oil in the spring lower leg.
RockShox recommends service intervals every 50 hours of use for the lower legs and every 200 hours for the damper and spring service.
On the back of the fork crown is the serial number than can be used on the RockShox TrailHead page
or app to return all service information, specification data along with recommended upgrade and service parts.
It's the same as nearly all other RockShox forks to service the lower legs and handle spring swaps. The Zeb needs 20ml of 0w-30 oil in both lower legs.
Picking a victor between the two forks is no easy task, with each fork having loveable traits in their character that I cherish. While neither fork is faultless, the ride arounds for each of the fork’s nuances is neither a hindrance or problematic. I’ve been switching back and forth between a favourite throughout the whole test, with it mostly aligning with which fork was bolted to the bike.
Both the 38 and the Zeb are brilliant offerings for this longer travel aggressive single crown category. But bringing in the factors of weight, price and setup alongside performance makes the Zeb stick its nose ahead of the 38.
It’s a cheaper and lighter package than the 38, with it getting me to a happy window so quickly and with such ease, which counts for a lot. Those recommended settings being pretty spot on and not far away from my prefered settings once testing had finished.
The performance of the 38 is certainly top notch and its composure on the trail while remaining supple and supportive is a gnat's whisker ahead of the Zeb. But not enough with all things considered, and it did take more tinkering to find that same happy window of operation, something that riders with less understanding of suspension and tuning might struggle to find. Especially with the final settings for the 38 being further away from the recommended ones.
There will always be diehard fans of either Fox or RockShox, and if you prefer a fork that is supple and feels like it’s doing its thing underneath you then the Zeb will be up your street. If you like your forks with a bit more of a stuck to the ground feeling and with more tinkering options then the 38 will provide you with what you’re after. All that said, with the editorial gun to my head it’s with the RockShox Zeb that I side.