FIRST RIDE IMPRESSIONS: THE ALL-NEW SPECIALIZED STUMPJUMPER 15

The coveted trail bike is back and more capable than ever

FIRST RIDE IMPRESSIONS: THE ALL-NEW SPECIALIZED STUMPJUMPER 15

Specialized hasn’t given the Stumpjumper platform a significant update over the last few years, mainly because it’s a tried-and-true trail platform that is loved by many around the world. Between the 130mm travel regular model and 150mm travel EVO model, it was a bike that could ride just about anything with poise (including snagging an Enduro World Cup win under Charlie Murray). However, after over three years of development by the 50-person-strong Specialized Ride Dynamics Team, the 15th iteration of the Stumpjumper is here. The goal? Further refine and highlight the positive attributes of the previous platform while minimizing or eliminating the negative traits. The geometry of the new bike isn’t revolutionary, but the Stumpjumper is now consolidated into a single 145mm travel family with a healthy dose of tech that aims to be the ultimate quiver-killer.

GENIE Shock 

At the heart of the new Stumpjumper 15 platform is the GENIE air shock, developed in collaboration with both the Specialized Ride Dynamics team and engineers at Fox Suspension, which aims to blend the best attributes of both an air and coil shock to increase the grip and capability of the bike using what they call “GENIE air spring technology.” Traditional in-line and piggy-back air shocks are touted for their lightweight and range of adjustability, but this often comes at the cost of small-bump compliance and traction through fast and rough sections of trail. On the other hand, coil shocks are known to have better small-bump compliance and help the back wheel hug the ground, but they are often significantly heavier than comparable air shocks and offer less adjustment. The GENIE shock aims to bridge this elusive gap to give the rider a platform that’s supple off the top like a coil shock with an increased and more progressive spring rate deeper in the travel, all while staying poppy and playful and retaining the ability to be fine-tuned by the rider. Specialized claims that the GENIE shock delivers a 57% reduction in traction loss, 16.3% better bump-force management, and a 39% decrease in severe bottom-out events compared to traditional air springs.

How is this done? Essentially, the GENIE shock uses two interconnected air chambers that dynamically adjust as the bike moves through its travel. In the first 70% of the shock’s stroke, both the inner and outer air chambers are active. This gives it a softer and more linear spring curve that soaks up small to medium-sized bumps like a coil shock, yet you can fine-tune it like a traditional air shock with volume spacers. As the GENIE shock compresses into the last 30% of its travel, the GENIE band closes off the air-ports and reduces the air volume to just the inner chamber, significantly increasing the spring rate. This creates a much more progressive spring curve and lets the shock handle big drops, impacts, and steep descents without a harsh bottom-out.

The chart above demonstrates the Stumpjumper 15’s rear wheel travel in comparison to the force exerted on the shock. At 1,080Nm of force, the Stumpjumper 15 uses 100mm of travel (the same amount as the current Enduro), whereas the previous Stumpjumper EVO only used 85mm. Put simply; this means you get more grip and compliance out of the rear end when the bike is in the “Bump Zone,” which Specialized defines as the range of bump forces that make up the majority of events on a trail ride (typically 800-1,300Nm of force). Despite using more suspension travel for a given force input in the first 70% of the travel, the progressive ramp-up in the last 30% prevents the bike from blowing through the end of the shock’s stroke and lets the entire spring curve be utilized.

Geometry & Frame Details

Looking at the Stumpjumper 15’s geometry numbers, there have been some subtle but effective tweaks to unlock even more descending prowess from the platform. The head tube angle sits at 64.5 degrees (middle setting), making it the same as the previous Stumpjumper EVO, and the seat tube angle sits between 76.5 degrees and 78 degrees (depending on the size) to put the rider in a balanced pedaling position. Stack height and head tube length are now taller relative to frame size (640mm stack height and 125mm head tube length on size S4), and the bottom bracket height is a tad lower at 337mm. Chainstay lengths are relative to each frame size, growing from 430mm on the size S1 to 445mm on the S6 (our test size S4 has 435mm chainstays), but the overall wheelbase for each size is essentially the same as the previous Evo frame.

Like the previous Stumpjumper, the new platform prioritizes integrated frame adjustability. A flip chip at the Horst Link lets the bottom bracket height be fine-tuned by +/—7mm to give you a bit more clearance on techy trails or more stability when speeds pick up, but the rest of the geometry remains the same. Size S1 and S2 frames come with a mixed-wheel setup, while S3-S6 frames have 29″ wheels. However, an aftermarket link kit allows the bike to run either configuration without altering the geometry. Also carrying over from the older Stumpjumper model are the adjustable headset cups, which let the new bike be a nimble trail weapon with a 65.5-degree head tube angle, a descent-hungry machine with a 63-degree head tube angle, or a versatile and more balanced platform with a 64.5-degree head tube angle.

The Stumpjumper 15 also includes the latest version of the SWAT downtube storage system, or SWAT 4.0 as Specialized calls it. The revised system features a more low-profile lid that is flush with the downtube for a sleek and integrated look, and the locking system uses a large lever that is easy and intuitive to use. The lid has standard mounts for a bottle cage with plenty of clearance, and a new sealing system makes it more weather-resistant than ever to keep water, dirt, and debris out of the downtube. Specialized includes their standard downtube storage bag to keep your tools and trail-side goodies safe.

As we’re sure you’ve noticed, the asymmetric “Sidearm” design of the previous bike has been replaced by a more substantial and symmetrical shock link; it almost looks like a beefed-up version of the brand’s new cross-country ripper, the Epic 8 EVO. The reason for this shift in design, according to Specialized, is that adding weight to reinforce the link in this way was more efficient in stiffening the frame than the “Sidearm” method. Basically, they claim that they were able to produce a stiffer frame with more predictable handling with less mass.

The previous Stumpjumper and Stumpjumper EVO were lauded for their pedaling efficiency and bump performance on technical climbs, so Specialized wanted to carry these characteristics over to the new model. To do this, they found a middle ground between the regular and EVO models. Anti-squat starts at just under 113% to give you a solid and efficient-feeling pedaling platform, and it steadily decreases as you progress through the suspension’s travel to handle technical climbing sections and square-edged bumps without losing efficiency.

Build Kits

Specialized offers five different build kits of the new Stumpjumper 15, along with an S-Works frame kit for $3,500, ranging in price from $5,500 for the Comp model all the way up to $12,000 for the full S-Works build. The components are definitely descent-focused, with all of the models having a powerful set of either SRAM Maven or TRP DHR-Evo brakes and burly Specialized alloy or carbon wheels.

The Comp model features a Performance version of the Specialized/Fox GENIE shock, along with SRAM’s new S1000 AXS Transmission setup (which was also released today). The Expert model sees an upgrade to a Performance Elite GENIE shock and fork with SRAM’s GX Transmission drivetrain, making it a viable middle-ground option. The Pro spec, which we have for testing, has Fox Factory suspension, XO Transmission, and Roval Traverse SL carbon wheels laced to Industry Nine 1/1 hubs. Topping the totem pole is the S-Works model, which gets the full XX Transmission treatment, Maven Ultimate brakes, Reverb AXS seatpost, and bespoke DT Swiss 240 hubs. For riders who just can’t live without a coil shock, Specialized is also offering a freeride-focused Öhlins build kit that is spec’d with a TTX 22 M coil (tuned by the Specialized Ride Dynamics team) along with an RXF38 M.2 fork with 160mm of travel. The other models with Fox suspension have 150mm forks.

First Ride Impressions 

As we mentioned above, Specialized sent us the Pro build kit of the new Stumpjumper 15 in the stunning Satin Green Tint / Metallic Sulphur paint scheme. It almost looks like the clear coat was accidentally splattered across the frame as they finished painting the bike, but rest assured this was done on purpose to give the bike a unique look. The downtube and head tube areas are beefier and more substantial than the previous version of the bike, yet it still feels lightweight and nimble when picking it up to put in the repair stand.

When initially setting up the GENIE rear shock, Specialized recommends running 18%-20% sag, which is a bit lower than most other trail bikes. This makes sense, though, since the linear nature of the first 70% of the shock’s stroke lets you run higher sag without feeling harsh. There are 14 clicks of rebound adjustment on the shock, and the compression has three different pre-set tunes to let you quickly switch between plush, neutral, and firm settings, depending on the trail. The beginning and middle of the stroke are also tuneable via the included volume spacers, but most of our initial rides were spent with just one spacer installed. There is also an easy-to-access climb switch to firm things up.

Climbing onboard the new Stumpjumper feels very familiar to the outgoing model; smooth and meandering fire and access roads are met with efficiency and a comfortable pedaling position, yet it tackles techy sections without a second thought. It feels eager to take on the next ascent, no matter how steep it is. We rarely reached down to flip the climb switch on the shock, except when we were deep into an ascent and needed that extra bit of efficiency to get us up that last steep bit. The bike felt easy to maneuver around rocks and other obstacles on the trail; we could place the wheels right where we wanted them, and the GENIE shock was predictable as we pushed the bike to get up and over sections that required more technique. Small bumps disappeared as well, with the anti-squat providing a fine balance of suppleness and support.

The Stumpjumper 15 really shined when the trail pointed back down. It’s hard to accurately describe, but it almost feels like a more lively and playful Enduro. The GENIE shock, with its dual chamber design, gives the bike incredible small-bump sensitivity and a noticeable improvement in grip, especially on high-speed sections. The back wheel seemed to hug the ground more and let us push through sections that we would otherwise back off in, yet it still felt poppy and playful when we wanted it to be. Especially through braking bumps, the bike felt settled and composed, like it wanted to hold its line instead of getting bounced around. Big impacts and big drops were also handled with surprising poise and composure. On jumps and drops that we thought would blow through the bike’s travel, the GENIE shock smoothly ramped up and handled the impacts without a second thought. We haven’t been able to find the limit on the rear end or experienced any harsh bottom-outs through our first few rides, though we do plan on spending some time aboard the Stumpjumper 15 at the bike park this summer.

Overall, we’re impressed with the new Stumpjumper 15. It’s eager to climb just about anything you can power up with comfort and efficiency, yet it descends like a bike with more than 145mm of rear travel. Even though it can handle rough and rowdy trails and big drops with confidence, it still rides like a true trail bike when you want it to be and can pop and manual its way through almost anything. It feels like a side-hit-hunter and a plow-hungry machine at the same time and is definitely a fun bike to ride. We plan on experimenting more with the included volume spacers for the GENIE shock, which gives you more ability to fine-tune the middle part of the air spring curve, along with the geometry adjustments, to see how they affect the bike’s handling characteristics. Be on the lookout for a long-term test and review of the new Stumpjumper 15 in the next few months as we push the new do-it-all machine from Specialized to its limits.

For all the nitty-gritty details on the new Stumpjumper platform, check out the Specialized website. 

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