July 24, 2024

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First Ride: Specialized Stumpjumper 2025 with New Dual-Chamber Air Shock

First Ride: Specialized Stumpjumper 2025 with New Dual-Chamber Air Shock
Arguably the most iconic name in mountain biking, the Specialized Stumpjumper celebrates 43 years of evolution with its latest release: the 15. Not only has the Stumpy evolved with this new generation, but the product lineup has also seen some consolidation, with the EVO designation no longer applied to the longer-travel variant of the Stumpjumper.

We’re back to the single-link Stump, with 145mm of rear travel across the board, and 150-160mm forks across the board. The geometry and tweaks are pretty much the same as the outgoing EVO, but the little details have changed and evolved. The biggest change comes in the form of revised kinematics, along with new shock technology to maximize ride comfort.

Stumpjumper 15 details

• 29″ or mixed wheels (S1 and S2 mixed only)
• Carbon frame
• Frame travel 145mm, fork 150-160mm
• Head angle 63-65.5 degrees
• Range 400-530 mm
• Chains 430-445 mm
• Seat angle 77 degrees
• Wheel size and tire geometry core chips
• Actual Weight: 31.2 lbs / 14.2 kg (S5)
• Price: $6,500-12,000 USD
• S-Works Frame: $3,500
Specialist.com

Frame Features

Things here look pretty much the same as the last generation EVO, with push-in headset cups that allow for ±1 degree head angle adjustment, a high/low flip-up slider to change the baseband height and head tube/seat tube angle, and a secondary market rocker link that lets you run a different sized rear wheel. The latter only applies to S3 and larger bikes, as the S1 and S2 options are hybrid wheels only.

The Stumpjumper includes the SWAT 4.0 system, Specialized’s most advanced in-frame storage solution to date. First seen on the Epic 8, this latest version of the SWAT system eschews any excess hardware mounted to the frame, instead the hatch door interfaces directly with the frame’s carbon, ensuring a snug fit, long life and excellent weather insulation.

One new detail on the Stumpy that’s sure to stir up some controversy is the elimination of mechanical shift cable routing — this bike is all about wireless shifting. The argument from the development team is that they believe the best shifting performance available comes from systems like SRAM Transmission, and that the best is what people deserve on this bike.

The bike uses a stock 200mm rear brake mount, which is a bit of a surprise given that almost all Stumpjumpers come with SRAM Maven brakes – which can provide a lot of power on a smaller 180mm rotor. However, running them with 200mm rotors front and rear wasn’t too much of a stretch on this bike.

Engineering

Like the outgoing Stumpy EVO, the Stumpjumper 15 implements a wide range of geometry adjustments built into the frame. The head angle can be deviated by 1 degree in either direction from the original 64.5 degree position, via a set of easily interchangeable cups that come with the frame. A flip-up bracket on the rear seatpost allows the rider to raise or lower the bottom bracket height by 7mm, while changing the head and seat angles by 0.5 degrees. All of this in conjunction makes for a very wide range of adjustments, so I’ll stick with the original numbers for now, which relate to the mid-head angle and high flip-up bracket position.

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As mentioned earlier, the new Stumpjumper’s head angle is 64.5 degrees—slack enough for just about anything while still maintaining deft control in flatter corners. The actual seat angle across all sizes is around 77 degrees, though the actual angle cast by the seat tube measures a little looser than that, landing somewhere around 70 degrees. Reach numbers range from 400mm to 530mm across the six-size range, with 25mm jumps between all but the largest, which measures 30mm. Stack heights are pretty high for Specialized, with head tube length growing significantly on the larger bikes.

The bottom bracket drop is 38mm on all bikes except the S1, which measures 41mm. Rear bracket lengths vary across the range, with the lengths on all six sizes being: 430mm, 432mm, 435mm, 435mm, 445mm, 445mm. Again, many of these numbers can be tweaked by the end user, with a variety of possible results as they experiment with combinations.

Comment design

In many ways, this is a familiar story, but the characters involved have evolved slightly to allow for a different outcome. Our main character – Shock – is the most noticeably changed element of the game here, with some new mechanics allowing for very linear movement.

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Great Quotes We learned a lot from developing the Levo SL in terms of leverage ratio. By moving to a slightly lower starting point and slightly less progression than our previous bikes, we saw improvements in consistency and control of travel feel across the travel range, regardless of shock type. It also helped reduce shock pressures a bit and make the shock setup process easier. The SL was of course developed around standard shocks without the Genie technology being invented at that point.

Going into the Stumpjumper 15, we wanted to bring these characteristics with us, again, regardless of shock type, so you can see the similarities between the Levo SL and the SJ 15 (we’re a little more progressive on the SJ 15). This lift rate works great with the standard shocks and also helps to highlight what the Genie has to offer. We don’t need more progression in the first part of the stroke with the extra volume, and the adjustable secondary spring ramp is extra insurance for any rider looking for maximum support later in the travel.

Steve Saltnick

Shock of the Jinn

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Given the linear nature of the Stumpjumper 15, it would seem necessary to implement a somewhat progressive spring to prevent the bike from bottoming out harshly and repeatedly. However, the team behind the bike went in a different direction and instead created a shock that takes full advantage of this linear lift rate. The first key element here is the shock’s massive air volume. This is the beer-can-sized outer air chamber, called the Extra Volume (EV) chamber. For the first 70% of travel, the shock’s inner air chamber and the Extra Volume (EV) chamber act as a single air spring, slowly ramping up as they compress through the bike’s travel. At that 70% mark, a sliding sleeve inside the shock closes off the Extra Volume chamber, isolating the much smaller inner air chamber. This creates a more progressive air chamber, allowing the shock to ramp up for the last 30% of travel and preventing you from running out of breath at the end of the travel.

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Specialized Ride Dynamics, the group behind the Genie shock absorber, has dubbed its sliding bushing technology Pneumatic Spring Assist. The potential of this technology extends far beyond the shock absorber itself, as demonstrated in a patent filed last year.

The Specialized Ride Dynamics team tested a wide range of construction options using early versions of the Genie shock absorber to decide on factors such as the transfer point between the large and small air volume and whether or not to build the shock on an additional platform. Ultimately, they decided to use the Float as the basis for the technology, as any additional benefit of the additional oil volume in the additional shock absorber was immaterial compared to the gains from the increased air volume. Fortunately, the Float is also widely available with a wide range of aftermarket parts, so it will be easy to find parts for any service needed.

While this clever technology allows the Genie shock to improve the Stumpjumper 15’s ride quality, that doesn’t mean the bike doesn’t work with other, more common shocks. I had the opportunity to test the bike side-by-side with both the Genie and the standard offerings, and while the custom-designed shock seemed more convenient, the standard options worked very well.

Building Sets

They’re all carbon, all with the same construction, but with plenty of variation in parts to distinguish the different levels of build. The S-Works frame is slightly different in its use of a carbon fiber rocker link to save weight, but otherwise the frames are similar across the range. Every bike, except the Öhlins design, comes with a Genie shock absorber.


Impressions of the trip

For the past two months, the Stumpjumper has been my go-to bike for both fast daily rides and long commutes. That tells me how much I’ve enjoyed the bike so far, but it also speaks to the platform’s adaptability. The combined geometry and suspension tweaks can fundamentally change the character of a bike, transforming it from a sharp-feeling trail bike to a capable downhiller all within the parameters of the original components. Geometry-wise, I find the original position works best for me and my riding terrain. The 64.5-degree head tube angle intuitively handles a wide range of trails, and still feels confident on steeper terrain. This is helped by the wide stack height, which keeps you in a strong upright position with good weight across the handlebars. My only complaint is the seat tube angle, which feels a little too slack for me. This is likely due to my somewhat high seat height and the actual seat tube angle being much slacker.

I’ve owned a previous alloy Stumpjumper EVO for years, and I fondly remember the many good rides I had on that bike. This one is better, especially in the shock absorption department. The geometry is pretty similar between the two, but the Stumpjumper 15’s ability to stay composed over very rough terrain is truly impressive. The bike also generates a surprising amount of stability for a 145mm bike, putting it up against the longest-travel bikes in my garage. While the suspension feels very active, I didn’t find it to be swaying or vague in pumping scenarios—it moves more than you’d initially expect. For those who want a smaller bike feel, it’s as simple as adding more spacers to the shock’s Extra Volume chamber and adjusting the air pressure.

Last weekend, I went on a ride that might just highlight the comfort, capability, and toughness of the Stumpjumper. At about 95 miles and 18,000 feet of climbing, it was one of the biggest rides I’ve done in recent memory, and I feel like I picked the perfect bike for the job. There were no quiet descents on the map, each with its own character and terrain differences. Running the bike in the standard geometry setting, with a single spacer in the shock, I felt the bike had enough grip to hit some important features along the way, while remaining efficient enough to not add extra work throughout the day. The occasional stat drop isn’t so much to inflate my weak ego, but to illustrate the all-around nature of the Stumpjumper—the ride was comfortable and enjoyable all day long. It’s worth noting that I played with the easy-to-reach lock-up switch on a couple of fireroad climbs, but ultimately preferred climbing with the shock open.

I have a lot of other thoughts on this bike, but I’ll try to save most of them for the full review. Stay tuned, as this bike is sure to see a lot of changes as I continue to play around with settings and modifications.