Specialized Stumpjumper 15 & Stumpjumper 15 Alloy

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Zack Henderson reviews the Specialized Stumpjumper 15
Stumpjumper 15 S-Works
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Review Navigation:  Specs //  Intro //  The Frame //  Fit & Geometry //  The Builds //  What We're Curious About //  Bottom Line
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Intro

It’s hard to think of a more iconic bike lineage than the Specialized Stumpjumper. My first proper mountain bike was a blue 1998 Stumpjumper M2 Comp handed down from my dad, and a chronological look at changes in the Stumpjumper’s design shows just how far mountain bikes have come in a relatively short while.

The prior-generation Stumpjumper had a fairly lengthy run, released in 2020 (MY2021). At least here in the Pacific Northwest, the EVO version of that latest Stumpjumper seems to be on the back of every other truck in the parking lot, with geometry adjustments and a Goldilocks 150 rear travel / 160 front combination that worked well for a huge swath of riders.

For its 15th iteration, the Stumpjumper gets a revamped frame design, lots of geometry adjustments, and new suspension tech called GENIE. And, after being initially launched as a carbon-only model, Specialized has released a more affordable alloy-frame version. Read on for more on the overhauled classic.

Zack Henderson reviews the Specialized Stumpjumper 15
Stumpjumper 15 Alloy Comp

The Frame

At least for now, Specialized’s new Stumpjumper 15 does away with the split between the Stumpjumper and Stumpjumper EVO. Initially released as a carbon-only option made from Specialized’s FACT 11m material, Specialized is now offering the Stumpjumper 15 with an aluminum frame, too.

Though the suspension is still a four-bar layout with a yoke driving the shock, Specialized has made some changes to the kinematics. Anti-squat is now between the levels offered by the outgoing Stumpjumper and Stumpjumper EVO, at roughly 105% at sag before falling off to under 78% at bottom out. That’s not low by any means, but it’s also not as high as a number of other bikes in the Trail segment, and we’ll be curious to see what that means as far as the balance between responsive pedaling and rear wheel tracking under power.

Zack Henderson reviews the Specialized Stumpjumper 15
Anti-squat curves for the new Stumpjumper relative to the outgoing models

We’ll talk more about sizing down below, as the smallest S1 and S2 sizes get mixed wheels while larger sizes are full 29”, but it’s worth noting that all sizes of the new Stumpjumper are both 29” and mixed wheel compatible via a swappable link. Specialized is making those links available aftermarket so that riders can swap wheel size configurations as they see fit.

The SWAT box that is nearly ubiquitous on Specialized bikes gets updated as well to the 4.0 generation seen on the Epic 8. Specialized is offering lifetime replacement of pivot bearings for the original owner across all models — a nice feature for folks who plan to keep their Stumpjumper for the long haul.

Zack Henderson reviews the Specialized Stumpjumper 15
Rear linkage with a fairly beefy brace reminiscent of the Enduro's upper link
Zack Henderson reviews the Specialized Stumpjumper 15
Another look at the shock yoke, and that new SWAT box design

GENIE Rear Shock Concept

One of the most significant changes with the new Stumpjumper is the GENIE rear shock technology — a new air spring design that effectively varies the volume of the rear shock throughout the stroke to blend the benefits of high- and low-volume spring designs in different scenarios. Understanding the proposed benefit here requires a bit of background on air spring design and tradeoffs, so let’s briefly dip into those more technical details before we get into GENIE.

Air springs have changed massively over time and with a lot of nuance, but in their simplest form, air springs employ two opposing air chambers, positive and negative, which affect the spring curve based on their proportional size. Negative springs are critically important to the early stroke feel of an air shock, but it’s the positive side where the GENIE gets interesting,, so we’ll focus there.

Most air-sprung shocks on the market use a fixed positive air volume, which can be adjusted using volume spacers. In the simplest terms, smaller volume shocks have much more progression, meaning that the force required to compress the shock increases significantly from the start to the end of travel. Because much of the air spring ramp-up comes at the end of the curve, that means that there’s often a compromise in getting adequate early and mid-stroke support versus being able to use full travel. Larger volume shocks have a more linear rate of progression, but the tradeoff with that more linear progression rate is that they can often lack support at the end of the travel. Cramming a bunch of volume spacers in the shock can help with that end stroke support, but essentially introduces the tradeoffs of a smaller volume shock.

Enter Specialized’s new GENIE concept. Working with Fox, Specialized has developed a proprietary way of having a rather high-volume air chamber which is reduced to a smaller volume in the final 30% of the shock’s stroke. With the GENIE shock, an inner air chamber is accompanied by a secondary outer sleeve that effectively creates a secondary, but attached air chamber that increases overall volume and creates a more linear air spring curve. At 70% through the travel, a sliding internal band blocks off the shock’s outer air chamber by covering the ports connecting the two chambers, closing off that external sleeve and shrinking the overall air volume. This abruptly shrunken available air volume creates a sudden increase in spring progression, resulting in a shock that starts off with a more linear air spring characteristic but ends as quite a progressive one.

Zack Henderson reviews the Specialized Stumpjumper 15
Key parts of the GENIE system
Zack Henderson reviews the Specialized Stumpjumper 15
For most of the travel, the GENIE system uses the full available air volume
Zack Henderson reviews the Specialized Stumpjumper 15
Near bottom out, the red sleeve covers the small GENIE ports, reducing available volume for more progression

It’s important to note that some shocks, like the EXT Aria, and several forks (Ohlins RXF 38, Manitou Mezzer, EXT Era) use a dual positive spring setup to allow more customization of that spring curve, with a secondary positive chamber that can be run at higher pressures to create a smoother and adjustable end-stroke ramp up. Those chambers, however, are ultimately still separate and require tuning of relative air pressures to get the desired behavior. Compared to these rare and often rather expensive designs, the GENIE system simplifies things by requiring the adjustment of only a single air valve. 

Specialized makes some pretty bold claims about this new tech, including promises of “57% less traction loss” and “39% fewer severe bottom-out events” relative to a standard air spring. Relative to the outgoing Stumpjumper EVO, the Stumpjumper 15 claims to use 16.3% more travel for a given impact, indicating a greater response to impacts. We typically don’t put much stock in claims like these because of the nuances of riding style, setup preferences, etc., so we’ll have to see for ourselves just how the new system performs on the trail. 

As a final note here, the GENIE-equipped shock is only available as an inline option (i.e., no piggyback for extra oil volume) based on the Fox Float shock, so it will be interesting to see how the big claims of performance hold up on more sustained and rough descents where inline shocks can start to heat up.

Fit & Geometry

Unsurprisingly, the new Stumpjumper follows Specialized’s S-Sizing concept, which encourages riders of different sizes to select a frame size based on individual proportions and riding preferences. While it’s really not functionally different from a typical Small, Medium, Large, etc. approach, it can help folks who tend to think “I’m a Large” consider geometry more fully when picking a frame size.

Folks familiar with the prior Stumpjumper EVO will recognize the familiar 2-position flip chip at the pivot between the chainstay and dropout. This allows for a 7 mm swing in bottom bracket height between Low and High settings, while an eccentric headset cup allows for 3 headtube angle options: 63° (Low), 64.5° (Mid) and 65.5° (High).

Outside of those adjustments, most geometry figures are in the range of what we’d consider normal for a modern Trail bike. With the reference position of the headtube in the Mid position and bottom bracket in High, the S4 gets a 475 mm reach, 640 mm stack, rather substantial 38 mm bottom bracket drop, and short 435 mm chainstays. Full geometry figures are included in the chart below:

Zack Henderson reviews the Specialized Stumpjumper 15
Geometry on the new Stumpjumper 15

The Builds

Stumpjumper 15 Alloy

The Alloy may be the more wallet-friendly version of the Stumpjumper 15, but Specialized has still done well to invest in some well-chosen (and unexpectedly burly) parts choices. 

Starting with the base model Stumpjumper Alloy, it comes with a RockShox Psylo Silver fork (140 mm travel on S1, 150 mm for all other sizes) but doesn’t get the new GENIE-equipped shock. 

The Comp Alloy build gets a Fox 36 Rhythm (140 mm on S1, 150 mm on all other sizes) along with the GENIE-equipped Fox Float Performance shock. The Alloy and Comp Alloy also feature Shimano MT420 and TRP Trail EVO brakes, respectively, both with 203 mm front rotors across sizes and 203 mm rear rotors on sizes S3 and up — S1 and S2 sizes get a smaller 180 mm rotor out back. 

As the burliest build, the Fox Coil Alloy gets you a 160 mm Fox 38 Factory Grip X2 fork, DHX Factory shock, and TRP DH-R Evo brakes with 220 mm front and 203 mm rear rotors across all sizes. That’s a very downhill-oriented suspension and brake spec for a bike with 145 mm rear travel. 

Zack Henderson reviews the Specialized Stumpjumper 15

Dropper post lengths are generous and size-specific, with S1 size getting 125 mm drop, while S2 gets 150 mm, S3 gets 170 mm, and S4 and above get 200 mm (or 190 mm on the Comp Alloy’s X-Fusion post). 

Interestingly, despite all-SRAM build options on the carbon version, the Alloy sticks with cable-actuated Shimano drivetrains across the board.

The full set of Alloy builds is as follows:

  • Drivetrain: Shimano Deore
  • Brakes: Shimano MT420 (w/ 203 mm front rotor, 180 mm rear on S1–S2 and 203 mm on other sizes)
  • Fork: RockShox Psylo Silver (S1: 140 mm travel, all others: 150 mm)
  • Shock: X-Fusion 02 Pro RL
  • Wheels: Specialized alloy rims w/ sealed cartridge bearing hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: TranzX (S1: 125 mm, S2: 150 mm, S3: 170 mm, S4–S6: 200 mm)
  • Drivetrain: Shimano SLX
  • Brakes: TRP Trail Evo (w/ 203 mm front rotor, 180 mm rear on S1–S2 and 203 mm on other sizes)
  • Fork: Fox 36 Rhythm (S1: 140 mm travel, all others: 150 mm)
  • Shock: Fox Float Performance GENIE
  • Wheels: Specialized alloy rims w/ sealed cartridge bearing hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: X-Fusion Manic (S1: 125 mm, S2: 150 mm, S3: 170 mm, S4–S6: 190 mm)
  • Drivetrain: SRAM GX Transmission
  • Brakes: TRP DH-R Evo (w/ 220 mm front rotor, 203 mm rear)
  • Fork: Fox 38 Factory Grip X2 (160 mm)
  • Shock: Fox DHX Factory
  • Wheels: Roval Traverse w/ DT Swiss 370 hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: PNW Loam (S1: 125 mm, S2: 150 mm, S3: 170 mm, S4–S6: 200 mm)

Specialized is also making the Alloy frameset available for $2,300 USD, which includes a Fox Float Performance GENIE shock.

Stumpjumper 15 Carbon

The carbon side of the Stumpjumper 15 family follows the same general build structure of the Alloy version, but with several tweaks.

All Carbon builds get the new GENIE shock and a 150 mm fork, except for the Ohlins Coil build, which comes with a TTX22 M.2 rear shock and an Ohlins RXF38 M.2 up front set to 160 mm travel.

Specialized also continues with prioritization of powerful brakes. All builds (except the TRP-equipped Ohlins Coil build) feature SRAM’s very powerful Maven brakes, and with a 200 mm front rotor no less. S1–S2 sizes get a smaller 180 mm rear rotor where S3+ sizes get a 200 mm one, but no matter how you look at it, that’s a whole lot of brake for a 145 mm rear travel bike. Like its Fox Coil Alloy sibling, the Ohlins Coil build gets TRP DH-R Evo brakes with a 220 mm rotor up front and 203 mm out back on all sizes.

Speaking of SRAM, cable-loving luddites among us will be saddened to know that the electronic revolution is officially here — with the carbon version of the Stumpjumper 15, every model gets SRAM’s Transmission in GX, X0, or XX trim depending on the build. Fortunately, the Alloy builds remain a cable-friendly option.

The same long dropper post lengths seen on the Alloy builds continue with the Carbon Stumpjumper 15, from 125 mm on the S1 to 200 mm on S4 and above (again, excepting the Comp build’s X-Fusion post which tops out at 190 mm). Pro builds come with Bike Yoke Revive MAX posts that eke out a bit more travel at each size (S2 gets 160 mm, S3 185 mm, S4+ 213 mm), but unfortunately the spendy S-Works Stumpjumper comes with the Reverb AXS which still maxes out at 170 mm. 

Highlights from each model’s available builds are as follows:

  • Drivetrain: SRAM GX Transmission
  • Brakes: SRAM Maven Bronze (w/ 200 mm front rotor, 180 mm rear on S1–S2 and 200 mm on other sizes)
  • Fork: Fox 36 Rhythm (S1: 140 mm travel, all others: 150 mm)
  • Shock: Fox Float Performance GENIE
  • Wheels: Specialized alloy rims w/ sealed cartridge bearing hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: X-Fusion Manic (S1: 125 mm, S2: 150 mm, S3: 170 mm, S4–S6: 190 mm)
  • Drivetrain: SRAM GX Transmission
  • Brakes: SRAM Maven Bronze (w/ 200 mm front rotor, 180 mm rear on S1–S2 and 200 mm on other sizes)
  • Fork: Fox 36 Performance Elite (S1: 140 mm travel, all others: 150 mm)
  • Shock: Fox Float Performance Elite GENIE
  • Wheels: Roval Traverse w/ DT Swiss 370 hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: PNW Loam (S1: 125 mm, S2: 150 mm, S3: 170 mm, S4–S6: 200 mm)
  • Drivetrain: SRAM GX Transmission
  • Brakes: TRP DH-R EVO (w/ 220 mm front rotor, 203 mm rear)
  • Fork: Ohlins RXF38 M.2 (160 mm)
  • Shock: Ohlins TTX22 M.2
  • Wheels: Roval Traverse w/ DT Swiss 370 hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: PNW Loam (S1: 125 mm, S2: 150 mm, S3: 170 mm, S4–S6: 200 mm)
  • Drivetrain: SRAM X0 Transmission
  • Brakes: SRAM Maven Silver (w/ 200 mm front rotor, 180 mm rear on S1–S2 and 200 mm on other sizes)
  • Fork: Fox 36 Factory GRIP X2 (S1: 140 mm travel, all others: 150 mm)
  • Shock: Fox Float Factory GENIE
  • Wheels: Roval Traverse SL carbon w/ Industry 9 1/1 hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: Bike Yoke Revive MAX 3.0 (S1: 125 mm, S2: 160 mm, S3: 185 mm, S4–S6: 213 mm)
  • Drivetrain: SRAM XX Transmission
  • Brakes: SRAM Maven Ultimate (w/ 200 mm front rotor, 180 mm rear on S1–S2 and 200 mm on other sizes)
  • Fork: Fox 36 Factory GRIP X2 (S1: 140 mm travel, all others: 150 mm)
  • Shock: Fox Float Factory GENIE
  • Wheels: Roval Traverse SL carbon w/ DT Swiss 240 hubs (S1–S2: mixed wheels, S3–S6: full 29”)
  • Dropper Post: RockShox Reverb AXS (S1: 125 mm, S2: 150 mm, S3–S6: 170 mm)

In addition to the complete builds, Specialized also offers an S-Works frameset version priced at $3,500, which comes with a Float Factory GENIE shock. 

Some Questions / Things We’re Curious About

(1) How does the feel of the novel GENIE shock compare to more conventional layouts, both in terms of performance and setup?

(2) How easy and impactful are the myriad adjustments baked into the new Stumpjumper?

(3) With the outgoing Stumpjumper and Stumpjumper EVO having different personalities and intentions, where does the new Stumpjumper 15 fit on that spectrum as far as ride feel — and where does it differ entirely?

Bottom Line (For Now)

For a lot of folks, the Specialized Stumpjumper and Stumpjumper EVO were an easy quiver-killer choice for folks on the borders of either the Cross Country and Trail or Trail and Enduro categories, respectively. While the new Stumpjumper does away with the EVO designation for now, it remains positioned as a versatile Trail bike with a relatively burly build spec, but with some interesting new adjustments and suspension features. While it seems Specialized hasn’t messed too much with a good thing, those changes have us intrigued — and we should be getting one in for review soon to find out.

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11 comments on “Specialized Stumpjumper 15 & Stumpjumper 15 Alloy”

  1. Does the frame have the ability to take a mechanical drivetrain with internal cable routing or is this fully setup for electric shifting? I much prefer the gear spacing of Shimano drivetrains.

    • No provision for a mechanical derailleur. SRAM T-Type has more than a few, shall we say, challenges, but at least they addressed the gear spacing in the lower ranges. But SUCH slow shifting. Argh!

      Gotta say, though I’m not a big fan of proprietary rear shocks, this Genie thing is getting really good initial reports. Let’s see what everybody is saying after six months.

  2. Here’s what I would do if I were pondering buying this bike: buy the Stumpy 14 frameset at a KILLER price and build it with a 140 piggy back shock and 150 fork you’re welcome. I ride this now and it slays. Plus its build size allows me to have a super capable TRAIL – not XC, not enduro – bike and add an actual more downhill-oriented bike to the quiver later. There is no “one bike to rule them all.” The quiver can’t be killed! Ha

  3. Specialized, turning on the non standard equipment switch again? It’s a bold move Cotton! Considering the market is currently flooded with 2023 inventory, we’ll see how well this genie floats!

  4. So the big question is: will there be an evo model? Indeed, they don’t say so now, but that doesn’t mean they won’t release it in the future.

    Although, historically most Evo versions of Spesh bikes, have had only spec, or perhaps a different rocker link, not a whole different frame. With the upped travel, I would not expect to see a different frame, but where are the Evo builds with a reservoir shock and such?

    • With the Alloy version now available, there are two builds (Ohlins Coil and Alloy Fox Coil) that satisfy that gap that the Evo used to fill. While there’s always a possibility of an Evo version coming down the line, the inclusion of these coil models seems to hint at the Evo disappearing from the lineup.

    • The prior-gen Stumpjumper uses a 190×45 mm shock and the new one goes up to a 210×55 mm one (or 52.5 mm stroke, in the case of the S1) so not for the time being.

  6. I’m confused how a frame that’s tuned to the progression and bottom-out support of a genie shock is supposed to be even betterer (and more expensive) downhill with a linear coil shock? Surely the frame’s kinematic is built to one or the other, particularly with such a distinctive air shock? If the air stock’s tagline was ‘feels like a coil’ à la Vivid I’d get it, but that’s not what the Genie detail says.

    The idea of a mini enduro sled with 38 forks sounds cool though. And the full RRPs seem reasonable.

    • Spot on. The marketing claims and “tech” explanation for this bike from Spec are ridiculous. It has a very linear/non-progressive compression curve which should mean the only coils that will be rideable are the Cane Creek Tigon or one with a progressive spring. Even with an air shock, I’m very skeptical of the Genie approach. It should lead to a bike that wallows in the mid travel. This will make it feel plush, with the end stroke ramp up preventing bottom out, but it will also feel sluggish, and doesn’t give the damper much room to actually absorb bump energy. That sounds to me like a bike that is comfy for slow riders but not actually performant for anyone fast. Also sounds like it’ll be bogged down on the climbs.

      Contrary to the Manitou, Ohlins, and EXT dual positive air chambers which *increase* air volume later in the stroke to create linearity and let you run initial volumes and pressures that support the midstroke, this Genie does the opposite, decreasing volume at the end. That means a high initial volume that reduces midstroke support and then “catches” at the end with a ton of progression. I’m very skeptical.

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