Wil Tests & Reviews The 2021 RockShox SID Ultimate Fork

It’s been four whole years since we last saw a properly new SID fork from RockShox. It’s no coincidence that 2016 was also an Olympic year, which seems to be the preferred timing for brands to release their new flagship XC product. There have of course been damper and spring updates to the SID over the past few seasons, but the fundamental design and chassis hasn’t changed since the 2016 release.

Fast-forward to 2020, and RockShox is ready to unveil the latest generation of its high performance XC race fork. Except, well, that’s only half of the story. Because there are actually two new SID forks for the 2021 model year.

The SID has previously been offered in both 100mm and 120mm travel variants, which have been based on a similar chassis with 32mm diameter stanchions. For 2021 however, RockShox has decided to split the lineup into two distinct fork platforms with two different names;

• SID SL – The 100mm travel XC race fork with 32mm upper tubes and a seriously low claimed weight of just 1326g
• SID – The 120mm travel XC/trail fork with 35mm upper tubes, a beefier chassis and a claimed weight of 1527g

As if that wasn’t enough, RockShox has also launched a new rear shock called the SIDLuxe. There’s a whole lot to cover in this 3-prong XC attack, so if you’re after an overview of the two forks and shock, along with a closer look at the new technologies and the different variants on offer, check out our big feature story on the 2021 RockShox SID fork and shock range here.

However, most of you are here to read about what this new SID is actually like to ride. Very handily, we were sent out a 120mm travel SID Ultimate a couple of weeks ago to put it through its paces on our local trails. I’ve been riding the heck out of it since then to see how it rides, to find out what’s improved, and how it compares to its main rival. More on that in a bit.

Firstly, What’s Changed Over The Old 120mm SID?

From the bottom of the dropouts to the tip of the steerer tube, the 2021 RockShox SID is an entirely new fork from the inside-out. New chassis, new damper, new air spring, new adjusters, new everything.

Compared to the previous 120mm SID, the new version has undergone a trail metamorphosis with the addition of 35mm upper tubes, the same outer diameter as what you’ll find on the Pike & Lyrik forks. Internally the stanchion tubes are butted to reduce weight, while the one-piece magnesium lowers are hollowed out for the last 8cm down at the dropouts.

Inside the right fork leg is the brand new Charger Race Day damper. Like the Charger 2.1 damper you’ll find in a Pike, it uses a closed cartridge design with a flexible rubber bladder that expands as it fills with oil under compression. However, everything has been shrunken down to the bare minimum. There’s less oil volume, smaller shims and a skinnier damper shaft, all optimised around the SID’s shorter travel. The slimification process has dropped a good chunk of weight – RockShox has saved nearly 100g in the damper alone compared to the previous SID.

There’s also a new DebonAir spring, which is designed to emulate the performance of the Pike & Lyrik more closely. RockShox has modified the positive and negative air volumes, and implemented a smaller and lighter seal head. The transfer port between the two air chambers has been lowered down slightly, which helps the pressures to equalise sooner and keep the fork riding higher in its travel.

In a further bid to minimise stiction, RockShox is now using Maxima Plush damping fluid and SKF wiper seals in each of the new SID forks.

So, How Light We Talking?

Despite the new SID beefing up considerably in stature, all of those clever material-saving tactics have actually brought the weight down. And not just a little.

Our 120mm travel SID Ultimate weighed in at 1525g with an uncut steerer and with the Maxle thru-axle installed. By the time I chopped it to 175mm, that weight came down to just 1501g. Compare that to the old 120mm travel SID Ultimate fork, which weighed in at 1695g. For the weight weenies out there doing the math, that’s a hefty drop of 10%.

RockShox says most of the weight savings have come from the Charger Race Day damper, as well as the new lowers and crown. The crown is made from forged alloy that is then post-machined to remove as many excess grams as possible. Oh, and if you’re wondering why there’s no carbon steerer option, here’s the word from RockShox; “Carbon parts take a lot of time to develop and we focused on the alloy crowns first. In looking at what we accomplished with aluminium, it will take more research to understand if we can achieve any performance or weight improvements with a carbon CSU.”

Given the low weight RockShox has already been able to achieve with the new SID Ultimate without going to a carbon CSU, I suspect we won’t be seeing one.

Installation Notes

RockShox continues to narrow its target user for the new SID, which is now only available for 29in wheels and with Boost hub spacing. Unlike other 29er forks from RockShox that are offered with both 42mm and 51mm offsets, the new SID is coming with a 44mm offset only. This decision was made based on “the fact that most of the industry is moving to shorter offsets for all bikes”, and to help simplify things for OE customers – RockShox wanted to offer a single offset, and it also wanted to be consistent with Fox, which produces a 44mm offset. So there you go.

One option that is available is a shorter air spring that brings travel down to 110mm. Apparently this is what the men on the Scott-SRAM team have been using, and it’s certainly an intriguing option for XC racers who might want a beefier option than a 32mm fork, but without going to the full 120mm travel.

Bolting on the SID is otherwise easy-breezy. I love the simple press-fit guide for the front brake hose, which requires no cable ties or tiny bolts to secure. The lowers use 180mm post-mount disc tabs, which means you won’t need an adapter to run a 180mm rotor. It’s very tidy, but it does mean you can’t run a 160mm rotor on these forks, not that I suspect will be an issue for most riders given this is a chunky 29er trail fork. Want moar powaaaah? You’ve got clearance to go up to a 200mm rotor on the SID.

The Maxle thru-axle uses a 6mm hex key to tighten and loosen, while the inside of the dropouts are Torque Cap compatible. With a matching front hub with oversized end caps, you increase surface area contact between the fork and the hub, which helps to boost torsional stiffness. I’ve used the Torque Cap combo on existing SID, Pike and Lyrik forks, and it does make a big difference to steering precision and structural stiffness for the fork. It’s unfortunately not a wide-reaching standard as of yet though. With a regular front hub, it just makes it slightly more faffy to locate and fit the axle.

RockShox says there’s enough space in the SID’s lowers to fit a tyre up to 2.45in (62mm) wide. I’ve got a 2.3in Bontrager XR5 Team issue tyre up front, and there’s plenty of mud room there. Speaking of, RockShox is finally offering an optional bolt-on mudguard! It looks bonza in the studio pics, but we’re yet to see one in real life or confirm aftermarket availability. We’ll update you here once we get word.

Setting Up SID

Thanks to those big volume 35mm stanchions, operating pressures for the new SID are pretty low. I weigh about 68kg ready to ride, and I ran just 66psi inside the DebonAir spring, as per the slightly-difficult-to-read setup chart on the back of the lowers. The recommendation was spot-on too. Standing up on the pedals, the fork sagged 25% into its travel.

A quick high-five here to RockShox for those brilliant sag gradients anodised onto the stanchions – it makes setup much easier, and I like that you’ve got a visual guide for where full travel is.

The new SID uses the same grey Bottomless Tokens as the Pike, and you get a couple included in the box. Our test fork arrived with no Tokens inside the air spring, and so I rode it like that to begin with, assuming that would be the factory setup. A cassette tool is all you need to open the air spring top cap and add Tokens should you need to.

Low-speed rebound damping is adjusted in the usual manner, though in the name of weight saving, it’s performed by a removable 2.5mm L-handle hex key. It isn’t particularly ergonomic or pretty, but it does the job. If you’re running a matching SIDLuxe rear shock, you can remove the fork’s rebound adjuster and use it to adjust the tooled rebound damping on the shock, which is pretty neat. As for the rebound setting itself, I went halfway at 10/20 clicks.

Aside from air pressure and rebound damping, there isn’t a lot else to adjust on the SID Ultimate. You won’t find adjustable low-speed compression, though there is a 2-position lockout lever that offers either Open or Locked settings. A remote option is also available, which gives you a TwistLoc remote for opening and closing the fork.

What’s Good?

From the very first ride on the 2021 SID Ultimate, it was evident that this is a very different fork to the outgoing SID.

For a start, it is vastly smoother than any other SID I’ve ridden before. Whereas the SID has always felt like it comes from a different family to the Pike and Lyrik, this new SID finally feels it shares the same DNA as its bigger siblings. In fact, I’d go so far to say it feels like a diet-Pike more than anything. Early stroke suppleness is quite incredible for a 120mm travel fork, with a cloud-like suppleness as the fork hovers over small chatter bumps and rubble. It is a very comfortable fork to ride with excellent bump reactivity.

Despite the supple feel to the first 30% of the travel though, the SID doesn’t give up its travel easily. The improved mid-stroke support from the new DebonAir spring is both obvious and welcome. You can feel the spring strengthen considerably as it pushes beyond the sag point, which helps to keep the fork from blowing through its travel – something the previous SID fork struggled with, unless you propped it up by loading it full of Bottomless Tokens. Early on I thought the fork’s plush feel and lack of low-speed compression damping would result in excessive brake dive, but since the spring is so supportive, it actually stays plenty composed.

Hitting bigger ledges and drop-offs, the SID continues to ramp-up nicely through the last third of its travel. Even with zero Bottomless Tokens inside, I couldn’t get it to bottom out once, and finished each ride with about 5mm left in reserve. One of my fellow testers, who’s got about 10kg on me, had exactly the same experience, and neither of us felt the need to add any Tokens – a refreshing change from other 32mm RockShox forks. My only concern is that folks who are much lighter and less aggressive in their riding style might find the SID too progressive.

Still, I think RockShox has brought a whole new level of performance with this new DebonAir spring. Along with the light damping, it gives the SID a nice supple action, noticeable mid-stroke support, and excellent end-stroke progression with no harshness to the travel even when absolutely romping into flat-landings. It handles feisty trail riding supremely well, with the 35mm chassis creating a strong connection between your grips and the front wheel.

What’s Less Good?

There is of course a limit to how hard you can ride this fork. The strong torsional stiffness and supple suspension performance do well to keep the SID tracking confidently on rough, rocky terrain, but it also encourages you to ride faster. That’s fine for the most part, but when facing off-axis impacts at high speed, the SID can start to choke a little.

I noticed this on a couple of rapid straight-line descents that were impregnated with numerous off-camber rock slabs – the kind of rock faces that do their best to bounce you around side to side like the bumper walls at a bowling alley. While the SID does well to hoover up most of those rocks, there was some occasional harshness when it took a surprise whack on an awkward angle. To me this felt more like binding from the chassis twisting under load, rather than spiking from the damper, since full-frontal impacts are swallowed without hassle.

To be fair, this was only during an extremely rough section of trail that I’d normally be riding a longer travel bike on. It is also a 1.5kg fork, with quite a bit less metal than a Pike, so that’s worth factoring in when considering what’s appropriate for your riding style and terrain. In general though, I found the steering precision to be superb with the SID, and it is a substantially stronger feeling fork than the previous 32mm SID. It’s also likely far more capable than most of the lightweight XC bikes out there designed to take a 120mm travel fork. Still, I’d like to get my hands on a Torque Cap compatible front hub to see how much of a difference it would make to the SID’s performance, since I’ve found it very effective with previous test forks.

Any other complaints? All those improvements in the chassis and internals doesn’t come cheap. The SID Ultimate as shown here sells for $1,499 AUD, and the remote lockout version goes for another hundred bucks more. To be fair, that’s about the same price as a Factory Series Fox 34 Float Step-Cast. The Aussie dollar has also had a rough time over the past 12 months (and specifically the last few weeks), so I’d brace yourself for some price rises on further 2021 product.

On the topic of pricing, RockShox is also offering the SID in a Select version that gets the cheaper Charger RL damper and a little less machining on the crown. That means it’s around 140g heavier, but it also means it’s cheaper at $1,199. You could always get that fork, and upgrade it with the Charger Race Day damper ($399 AUD) down the line if you fancied. Also of note for owners of a current RockShox SID or Reba, is that the 32mm Race Day damper is also backwards compatible with any post-2014 RockShox fork with 32mm stanchions and 100-120mm of travel, which is fantastic to see.

RockShox SID vs Fox 34 Float Step-Cast

Given the new SID’s 120mm travel, low weight and 35mm chassis, it’s an obvious competitor to the Fox 34 Float Step-Cast (SC). Having launched back in 2018, the 34 Float SC established a new performance benchmark for lightweight trail forks, and has become a popular choice on short-travel XC bikes like the Trek Top Fuel, Yeti SB100 and Specialized Epic Evo. It’s an exceptionally good fork that has been relatively unchallenged over the past two years.

With that in mind, we decided to do some back-to-back testing between the SID Ultimate and the 34 Float SC to see how the new RockShox fork stacks up against the current market leader. We tested the two forks on my Santa Cruz Blur and on Ben’s Trek Top Fuel – two bikes that are ideally suited to this new breed of lightweight short-travel trail forks.

Weight: Here the SID Ultimate wins by a country mile. Or 130g to be exact. At 1501g, it is a decent bit lighter than the 34 Float SC fork, which weighs in at 1631g with the same length steerer tube. If weight is a priority to you, the new SID wins.

Adjustability: The 34 Float SC is the more adjustable fork of the two, given it has a 3-position compression lever along with a separate low-speed compression dial. That allows for greater fine-tuning for different trails and racecourses, without necessarily having to flick the lockout lever so much. In comparison, the SID Ultimate is just open or locked. Because it is so active in the open mode, I do think the SID is a great candidate for the TwistLoc remote, particularly if you’re racing. Both forks have a nice, solid lockout that will open up if you hit something hard enough.

Plushness: In back-to-back testing, the SID had a smoother feel with better small-bump sensitivity. The 34 Float SC is by no means a harsh fork to ride, it’s just that the SID is better. On choppy terrain, it has a lovely flutter around the sag point that is very reminiscent of its bigger travel siblings.

Support: Out of the box, the SID’s DebonAir spring feels bob-on, with excellent mid-stroke support as you push past the sag point, and a strong ramp-up towards the end of the travel. In comparison, we found it easier to bottom out the 34 Float SC, even with 2-3 volume spacers inside. For riders less inclined to crack open their forks and mess around with spacers, the SID is more set-and-forget.

Stiffness: There isn’t really a lot separating these two forks, and we can’t say there are any glaring differences when you’re pushing them both hard. Both forks will twist and deflect a little more than their beefier counterparts, and a lot of that comes down to the more skeletal chassis, particularly around the hollow dropouts. Given their weight and intended application though, they both track well and offer excellent torsional rigidity. I’d like to try out the SID with a Torque Cap front hub, which I suspect would give it a noticeable edge over the Fox.

Damping Control: While both forks offer an active and compliant feel, if I’m really splitting hairs, I did feel that the FIT4 damper in the Fox offers a slightly more controlled ride quality on high-speed chatter, where it felt like it was recovering more effectively on repeated stutter bumps. This could also be chassis related, but I’d really need to do more testing on the SID, particularly on some nice long descents to try and get some heat into that Charger Race Day damper to see if fade is an issue. Otherwise in standard XC racing and everyday trail riding conditions, it’s performed its job without issue.

Flow’s Verdict

Structurally, visually, and performance-wise, the new RockShox SID is a massive step up from its predecessor. Not only is it significantly lighter, it’s also plusher, more supportive, easier to setup, and more direct in its handling too. It’s a better fork in every single way.

It also compares favourably to the Fox 34 Float Step-Cast, which has largely been uncontested for the past two years. With pricing on a pretty level playing field, the SID is the fork that I’d choose in a head-to-head comparison. Not only is it lighter, it’s also smoother and it has better mid-stroke support too. It has thoroughly impressed, and I suspect this will become a popular light trail fork that we’ll be seeing a lot of as stock equipment on 2021 model year bikes.

For the real XC purists out there reading this, take note – we’ll also be getting our hands on the even-lighter 100mm travel SID SL fork, and the SIDLuxe shock in the near future, so stay tuned for a full test on those. Needless to say, expectations have now been set quite high.

Mo’ Flow Please!

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