RockShox BoXXer Ultimate review

The latest RockShox BoXXer gets a design overhaul to keep it in the downhill fork fight

This competition is now closed

By Luke Marshall

Published: August 3, 2023 at 3:00 pm

To keep the BoXXer Ultimate in the downhill ring, RockShox has overhauled its longest-running suspension fork model with an all-new burlier 38mm chassis and DebonAir+ twin tube spring. It also gets tech adopted from the brand’s other forks, including the enduro-oriented ZEB.

Throughout the BoXXer’s redesign, World Cup stars Loris Vergier and Vali Höll helped steer the fork’s ride behaviour to this final product in a bid to keep them battling for wins between the tapes.

However, downhill forks aren’t just for the racers these days, and RockShox wanted to give those who lap the bike parks, and e-bikers who strive to get gnarly a fork that will boost their experience on the trails too.

The first and most notable update to the BoXXer Ultimate is the new 38mm stanchions the chassis is built around.

RockShox didn’t set out to make the stiffest fork possible, but instead one that delivers the control its riders want, while making sure the whole package isn’t too unforgiving.

RockShox says the stanchion-wall thickness and lower-leg design have been optimised to blend torsional and bending stiffness with compliance and comfort.

Other new features of the chassis include the stanchion crown height gradient markings and Lower Leg Plugs. The markings enable you to set the stanchion heights equally without needing to measure anything.

The Lower Leg Plugs are a simpler and cleaner way to remove excess air build-up in the lower legs. These dials unthread rather than requiring you to depress a button, which was known to weep oil and prone to sticking on the previous design.

The new chassis is available for 27.5in and 29in forks. It dishes out 200mm of travel as standard. However, you can buy a 190mm or 180mm travel-reduction spring kit for the BoXXer.

There are three offset options: 44mm (27.5in), 48mm (27.5in and 29in) and 52mm (29in). The crown comes in two specifications, tall and short. I tested the short option (flat upper crown).

The crown is machined down to minimise weight and anodised for a strong and smart aesthetic.

The fork also gets a bolt-on fender, can run a maximum brake rotor size of 223mm, and uses the existing 110x20mm RockShox Maxle.

With the BoXXer’s 38mm stanchions, RockShox had to develop a new spring to achieve the linear spring curve it wanted. This is because the large internal air volume of the 38mm stanchion was too soft in the mid-stroke and too progressive at the end of its travel.

This new DebonAir+ twin tube spring is a cartridge that enables RockShox to fine tune the negative, positive and casting volume (air trapped inside the lower legs) to provide a more linear spring curve.

Because the internal walls of the stanchions are no longer an integral part of the spring, this enabled RockShox to drill oil flow ports in the upper tubes. These holes allow oil in the lowers to circulate and keep the upper bushings lubricated to reduce friction.

It also enables air in the lower legs to equalise above and below the bushings, which should reduce additional progression of the air in the fork’s lowers, giving a more consistent feel.

The BoXXer Ultimate also uses Ultra-low Friction SKF wiper seals for smooth operation and Maxima Plush Damping Fluid and Dynamic Suspension Lube.

The Charger 3 damper found in the BoXXer Ultimate is identical to the new dampers in RockShox’s ZEB and Lyrik forks, although it’s longer and has its own shim tunes.

The rebound tune has been altered to work with the new DebonAir+ twin tube spring, but RockShox hasn’t provided details on specific compression tunes.

The high- and low-speed compression circuits are independent though, and adjusting one doesn’t influence the other. RockShox has managed this by designing the high-speed and low-speed compression oil flow ports sequentially.

So, you should be able to fine tune your fork without needing to find a compression-damping compromise.

The BoXXer Ultimate also uses RockShox’s new ButterCups technology to minimise vibrations felt through the fork. These are small rubber pucks that sit between the air and damper shafts and the lower legs, with the aim of reducing buzz from the trail before it’s transferred into the spring and damper.

I tested the RockShox BoXXer Ultimate at the famous Whistler Bike Park, in British Columbia, Canada. The weather conditions were as varied as the trails, and ranged from wet and slick to dry and dusty.

I tested a 29in version with 200mm travel and a 52mm offset on a GT Fury, putting the fork to the test over several days on everything from blue trails to the park’s wildest double black diamond and pro line trails.

With the new BoXXer being included in the RockShox TrailHead app, I entered the fork’s serial number and got the recommended air pressure and rebound adjustment for my 75kg (kitted up) weight. The TrailHead app suggested starting at 135psi and 10 clicks of rebound from fully closed.

I started with the high- and low-speed compression damping fully open, which is usual for me. After the initial laps, I felt the fork was a little too soft on the harder compressions, so RockShox suggested adding 10psi and I settled on 145psi. I kept the rebound at 10 clicks from closed and found this setting suited me.

When I got on the bike and had my first few bounces on the BoXXer, before even making it to the lifts, it was clear the fork is exceptionally smooth and quiet.

Once I’d found my preferred setup, which was easy to do, I felt comfortable on the fork from the get-go.

Over the test days, that never changed and the BoXXer gave a ride feel that calmed the front of the bike, delivering an easy to ride and reassuringly predictable fork. Something essential when you’re charging at full speed down unpredictable trails.

The updates to the fork certainly give it a different feel from the previous model. The breakaway force remains minimal and the fork slides easily into its initial stroke. However, after the first centimetre or so of travel, the ride character starts feeling different with the new BoXXer.

The new spring and damper give the fork a taller ride height, propping up the front of the bike. This initial portion of travel is the hardest feature of the fork’s performance to explain.

The BoXXer Ultimate’s beginning stroke is smooth and comfortable, and takes the sting out of small, high-frequency washboard bumps impressively well. Think of fast blue-grade bike parks that have had thousands of bikes rolling down them.

The ButterCups help here I’m sure, and it would be interesting to see how the non-Ultimate RockShox BoXXer model performs on the same trails, because it forgoes this tech.

Still, somehow it offers great support and rides higher, even while feeling plush and supple at the start of the stroke. RockShox has pulled off an impressive feat here in balancing early comfort with support. It’s one of the biggest improvements to the fork.

This suppleness is great for delivering traction through unsupported corners, and minimising vibrations through the handlebars. The support also enabled me to feel confident loading the front end on loose sections of trail or on awkward off-camber rocks.

As I started pushing the fork on rougher trails into bigger bumps and harder compressions, the smooth progression continued to a firm but not harsh mid-stroke.

The taller ride height is also great for keeping plenty of travel in reserve for these square-edge hits.

The mid-stroke is where I really noticed how composed and supportive the new BoXXer is. The more linear nature of the spring curve comes into its own here. The plush yet supportive middle part of the travel gives the fork its predictability on the trail.

This was ideal when charging rough sections of trails with plenty of rocks, roots, small drops and braking bumps. The BoXXer soaked up the hits while delivering plenty of comfort and support to push against.

RockShox doesn’t recommend adding tokens for end-stroke progression, unless in extreme cases for perhaps the fastest racers or heavier riders, and for my setting I didn’t need tokens. Deeper in the travel, that constancy in progressions gives the forks a smooth ramp-up without leading to a harsh bottom-out.

Landing big drops and jumps, or high-load compressions, there’s no noticeable harsh ramp-up or firm end stroke. The linear nature of the spring gives the fork a feeling that it only uses the travel required for each bump or compression. No more, no less.

Overall, it’s this consistent and smooth movement through the travel that gives the BoXXer Ultimate its impressive ride character.

The fork gave me tons of confidence to hit wild lines, knowing it would be unfazed by whatever was put in its path. Small, medium and large bumps and compressions were dispatched with control and composure.

While I chose to not use the compression settings for my preferred feel on the trail, I did fiddle to see what difference they made. The low-speed compression dial provides noticeable resistance to the fork’s compression through high-load berms and jump faces.

I felt this after four clicks out of the 15 positions available on my test fork.

This enables you to carry speed on smoother sections of trail, but decreased sensitivity.

The high-speed compression firms up hard landings and drops, which I didn’t find to my liking. There was enough support from the spring that I tuned that off quickly. Still, it’s good to know it’s effective if you need it.

What was impressive was the rebound speed of the fork. Usually, I run my forks faster than the recommended setting, but with the BoXXer I remained on the suggested settings, which gave me plenty of return speed to help keep the fork riding high in its travel, and enabled it to recover from repeated hits on the trail.

The new BoXXer chassis is also impressive, and no doubt plays its role in the fork’s overall performance. There was plenty of accuracy to the handling and it could hold a line, whether cutting across slippery rocks and loose turns or changing lines in tricky sections, or after poor line choices.

However, the 38mm stanchions and chunkier legs never beat my hands up more than I would expect, and I could hold on to the grips with full control for the long descents of Whistler’s trails. The chassis and performance have produced a comfortable, yet direct-handling fork.

This impressive handling meant I was confident changing lines when needed, and I didn’t notice any unwanted flex through high-load compressions or binding through hard repeated hits.

I found I used the Lower Leg Plugs often because they were so easy and simple to operate. These are a good update over the buttons you previously had to press.

Unfortunately, on my fork the rebound dial became stiff and creaky, and will need to be investigated at some point. It didn’t hinder performance, but I don’t think it’s designed to be like that.

Without doubt, the Fox 40 Factory and RockShox BoXXer Ultimate are the biggest rivals to each other. Before the new BoXXer Ultimate, the 40 Factory had the edge with its smoother spring and less pronounced ramp-up deeper in the travel.

Still, the BoXXer’s new spring and chassis, BoXXer-specific Charger 3 damper, and tech updates see the fork leapfrog the Fox. It offers plenty of support like the Fox, but it feels more plush and predictable over a wide range of trail features. It’s also more comfortable over long runs and doesn’t feel as if there’s a compromise to its handling for this.

It’s easier to set up, and the rebound speed is better suited to a wider range of spring pressures. The new BoXXer delivers a knockout blow to the Fox 40, for now, but it’s still a good fight.

The new RockShox BoXXer is the best downhill fork I’ve ridden to date.

It’s supremely comfortable with plush travel that still delivers predicable support. This gave me tons of confidence to charge lines and hit features that I may have thought twice about before.

Its handling and composure are thoroughly impressive. RockShox has created a brilliant fork here.

Technical writer

Luke Marshall is a technical writer for BikeRadar and MBUK magazine. He's been working for both titles since 2018 and has over 20 years of mountain biking experience. Luke is a gravity-focused rider with a history of racing downhill, previously competing in the UCI Downhill World Cup. Educated to a degree level in engineering and with a penchant for full-throttle speed, Luke is more than qualified to put every bike and product through its paces to bring you informative and independent reviews. You'll most likely find him on a trail, enduro or downhill bike riding the off-piste tracks around south Wales and the south west of England. He often makes an appearance on BikeRadar's podcast and YouTube channel.