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Specialized Stumpjumper 15 Redefines Trail Bike Capability w/ Genie Rear Shocks & Adjustable Geo

Specialized Stumpjumper 15, berm
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The first Stumpjumper debuted 43 years ago in 1981, and this is the 15th full-suspension iteration of the bike. After three years of development, Specialized has taken possibly their most proven bike and made thoughtful refinements to make it even better. The new Stumpy is an efficient pedaling trail bike, but through its adjustments and clever suspension tech, it can handle a lot more than your average 145mm travel MTB.  

Specialized Stumpjumper 15 – Frame Features:

Specialized Stumpjumper 15, link

The Stumpjumper 15’s front and rear triangles are constructed from FACT 11m carbon fiber. One noticeable update is how there is no more asymmetrical ‘sidearm’ support bridging from the seat mast to the top tube. Specialized said they were very happy with the previous design, but realized they could move the material from the sidearm into the Stumpy 15’s beefed-up shock link and achieve the same strength and stiffness with a cleaner look.  

Specialized Stumpjumper 15, S-works, side

Sticking with Specialized’s long-standing FSR suspension linkage, the 2025 Stumpy has been bumped to 145mm of rear travel. All models come with 150mm forks on frame sizes S2-6 and 140mm forks on the smallest S1 size. The Ohlins Coil model is another exception, which has a 160mm fork on all frame sizes.

Like many brands these days, Specialized is going with MX wheels on smaller sizes (S1 and S2) and stocking all larger sizes (S3 – S6) with 29” wheels. However, the larger frame sizes are mullet compatible by swapping to aftermarket shock links. The links keep the Stumpy’s geometry and suspension characteristics the same between either wheel size.

Specialized Stumpjumper 15, headset
Photo: Steve Fisher

Another key addition to the Stumpjumper 15 is its adjustable head tube angle. By swapping the headset cups, you can choose between neutral or +/- 1° cups. Between the cups and BB height flip-chip, the steering angle can vary from 65.5° to a very slack 63°.

Fitments and Frame Protection:

Specialized Stumpjumper 15, cable routing
Photo: Steve Fisher

If you like the new Stumpy, I hope you like wireless shifting too because there is no routing for a derailleur cable on this frame! The routing for the brake hose and dropper post cable is sleek and tidy. Straight entry holes on the head tube keep the hose/cable from rattling or rubbing on the frame.

As for frame protection, the Stumpjumper 15 comes with chainstay and seatstay guards plus a mudflap behind the BB to keep rocks out of your linkage. It also gets a lower down tube protector, and a clear protective sticker covering the underside of the down tube. Specialized also includes Fox’s front fender on the Stumpy Pro and S-Works models.

Frame fitments include 148mm Boost rear axles, BSA 73mm threaded BBs, and SRAM UDH derailleur hangers. Specialized specs several dropper post brands on different Stumpy models, so check out their website for the travel numbers. The frames accept 34.9mm seat posts.

SWAT 4.0 Frame Storage:

Specialized Stumpjumper 15, SWAT 4.0 storage

Specialized has redesigned its SWAT storage door and latch system, which now has a clean flush-mounted look. The latch now grabs directly onto the frame. If that sounds questionable to you, rest assured Specialized extensively tested it to ensure mud, dust, snow, etc, does not hamper its operation or damage the bike at all.

The down tube offers ample space inside for ride essentials. My test bike (S3 frame) easily fit a large c02 canister, inflator, plug tool, spare plugs, a spare battery for the AXS shifter, and a multi-tool, with room for more. Specialized supplies a zippered tool bag for in-frame storage.

I was happy to find the S3 frame easily accepts a large water bottle, with ample room to access it.

Genie Rear Shock:

Specialized Stumpjumper 15, Genie shock on bike

The Stumpjumper 15 features a new Fox Float X Genie rear shock, which is a patent-pending technology developed by Specialized. While the Genie shock was developed for this bike, the new Stumpjumper can run any rear shock including coils. That’s partly why Specialized specs one model with Ohlins coil suspension.

Now here’s what’s special about the Genie shock: It features an outer positive air chamber and an inner positive air chamber. They work together while you ride, as the outer chamber closes off when you hit about 70% travel. This causes the shock to essentially shrink its air chamber and create a ramp-up effect to increase bottom-out resistance.

Specialized Stumpjumper 15, Genie shock, open

During the initial stroke, the Genie’s two air chambers are both open and provide a large volume of air, offering a flatter spring curve for the first 70% of the stroke. This ensures sensitive, coil-like bump management throughout smaller and mid-sized impacts.

Specialized Stumpjumper 15, Genie shock, closed

When you reach 70% travel, a sleeve inside the shock called the Genie Band slides up and closes off the Genie Air Port holes leading to the outer air chamber. The air volume in the shock is reduced to the inner chamber only, creating a highly progressive spring curve.  

Specialized Stumpjumper 15, Genie shock, spacers
Photo: Steve Fisher

Controlling the first 70% of the stroke, the outer air chamber’s spring rate can be adjusted separately from the inner air chamber with up to four clip-on volume spacers. This allows riders to choose between maximum bump sensitivity or a more supportive ride feel. Adding or removing these volume spacers is a pretty easy job most riders could handle without a shop’s assistance. The inner air chamber’s bottom-out resistance can be independently tuned with eyelet volume spacers.

In addition to the unique aspects of the Genie rear shock, it also comes equipped with a two position switch (with a pretty firm climb mode) and a three position open mode adjustment (on all but the Comp model).

Suspension Characteristics:

Specialized Stumpjumper 15, FSR linkage
Photo: Steve Fisher

Specialized designed the new Stumpjumper to capably handle rough terrain and big impacts, yet maintain the poppy ride and efficient pedaling of a shorter travel bike. The Stumpy aims to offer sensitivity to small and mid-sized bumps, the ability to eat up square edged hits, and a bottomless feel on big drops.

By the numbers, Specialized says the Stumpjumper 15 offers 16.3% better bump force management and 57% better traction than the Stumpjumper EVO (meaning 57% less traction loss time between impacts). Due to the rising rate in the last 30% of the Genie shock’s stroke, Specialized reports 39% fewer severe bottom outs than a traditional air spring.

Specialized Stumpjumper 15, wheel force chart

The softer initial stroke of the Genie shock requires less force to move the rear wheel than the Specialized Enduro or Stumpy EVO. This means the new Stumpy is more willing to use initial/mid-travel to suck up impacts and provide a smooth ride. The numbers show when the Genie-equipped Stumpy 15 is hit with a 1,080 Newton impact, the bike will use 100mm of travel to absorb it, while the Stumpy EVO will use 86mm of travel. This eagerness to use its initial and mid-stroke helps the Stumpjumper 15 achieve its feeling of having more travel than it actually does.

Specialized Stumpjumper 15, anti squat chart

Of course, pedaling efficiency is of key importance for a trail bike. The Stumpy 15’s anti-squat was tuned to sit between the previous Stumpjumper and Stumpy EVO.

Geometry:

Specialized Stumpjumper 15, geometry chart
*Please note the above geo chart shows all figures for the Stumpjumper 15 in its neutral headset setting and High BB position. Read below to find out how those settings affect the frame geometry. Also, please note the geo for the Ohlins model is a bit different due to the longer 160mm fork. See the Specialized website for that model’s geometry.

The Stumpjumper 15 will be available in five frame sizes – S1 to S6. Specialized keeps the head tube lengths and standover heights somewhat close across the size range so riders can choose the reach/wheelbase that suits their style best. You can opt to go shorter for nimbler handling, or longer for more stability.

With the Stumpy’s adjustable headset angle and BB height flip-chip, there are six different geo configurations possible. The swappable headset cups offer a neutral setting or +/– 1°. Combined with the BB height chip the Stumpy’s steering angles can vary from 63° to 65.5°. That’s an excellent range for a modern do-it-all trail bike.

Specialized Stumpjumper 15, flip chip
Photo: Steve Fisher

The BB is fairly low in either setting at 337mm in High position or 330mm in Low. Moving from High to Low also slacks the bike out by 0.5°.

Reach numbers are up-to-date but not crazy, and given the S sizing scheme, you’re not stuck with a certain size based on your height or inseam. At 5’10” I find myself in the middle of the S3 and S4 frames. At 450mm the S3 (which I’m testing) is on the short side for me, but at 475mm the S4 would be lengthy. Both, however, are perfectly within reason for someone my height. As a consumer, I’d definitely want to test ride both before making a decision.

Seat masts angles vary slightly between frame sizes, but range from 76.5° to 77.6° (in neutral/High position). The Stumpy 15 sticks with shorter chainstays across the board. Specialized offers three different rear end lengths ranging from 430mm (S1) to 445mm (S5 and S6).

Build Notes/Components:

Specialized Stumpjumper 15, Maven brake
Photo: Steve Fisher

I noticed something about the Stumpjumper’s build specs; Specialized doesn’t want anyone thinking they have to limit themselves on this bike. For a competitive bike in the trail category (my Pro model test bike is under 32lbs), it’s got some beefy touches.

First of those would be the SRAM Maven brakes, with 200mm rotors front and 200/180mm rears (size dependent) for incredible stopping power. Note the Ohlins model comes with TRP DH-R EVO brakes on 220/203mm rotors. Specialized also equips the Stumpys with wide bars, at 780mms on S1 and S2s and 800mms on all larger sizes. The higher-end models’ SRAM XO and XX cranksets also include bash guards, but one thing not included is a chain guide.  

Specialized Stumpjumper 15, Roval Traverse SL II wheels

The Stumpy 15 Pro and S-Works models roll on pinch flat-resistant Roval Traverse SL II wheels. These rims’ Flat Top bead profile requires 85% more force to pinch a tire vs. standard round bead rims. The front and rear rims are specific, and the wheels offer vertical compliance. The rims are also designed to ‘ankle’ side-to-side to improve traction on uneven surfaces.  

Specialized specs all the new Stumpys with their Butcher (front) and Eliminator (rear) tires. Grid Trail casings and 2.3” widths come stock.

Model Lineup:

There will be five builds of the Stumpjumper 15 and an S-Works frameset available. Visit Specialized’s website for full build specs on each model.

  • S-Works Stumpjumper 15 – $12,000
Specialized Stumpjumper 15, s-works, angle
  • Stumpjumper 15 Pro – $9,000
  • Stumpjumper 15 Ohlins Coil – $8,500
Specialized Stumpjumper 15, Ohlins Coil
  • Stumpjumper Expert – $6,500
  • Stumpjumper 15 Comp – $5,500
  • S-Works Stumpjumper 15 Frameset – $3,500
Specialized Stumpjumper 15, big drop
All images c. Specialized Bicycles unless noted otherwise. Rider: Austin Hackett-Klaube.

I’ve been riding the Stumpjumper 15 Pro for a month. Be sure to check out my review article to see how it performed on-trail.

specialized.com

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11 Comments
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Austin Garner
Austin Garner
17 days ago

So the idea behind the shock is less mid-stroke support? I thought all these companies were looking to increase mid-stroke support from air shocks? This bike would likely feel great for small bump.

Grillis
Grillis
16 days ago

Wireless only? That’s a no for me dawg.

David
David
16 days ago
Reply to  Grillis

Same, not interested in electronics on my bike thanks.

Xc_racer
Xc_racer
16 days ago

Why is it that no manufacturer can get pad sweep centered on the rotor anymore?
It looks so garbage when there’s a strip of unused rotor…. and it likely also means there’s a strip of unused brake pad too.

hellyeahbrother42069
hellyeahbrother42069
14 days ago
Reply to  Xc_racer

Only looks that way from the side. The edge of the rotor crests the top of the pad like it should

Billyshoo
Billyshoo
16 days ago

I liked the sidearm design; it was good-looking and unique. But WOW, the paintjob on this thing is gorgeous and very cool!

David
David
16 days ago

It’s interesting to see the evolution of the ‘trail bike’ term into something more focused on down hills. It seemed like when the phrase was first used it described a bike which wasn’t an XC bike but that you could use all day but be a bit more confident while descending, but now it’s more like a gravity shuttle as evidenced here. No value judgment, it’s a valid riding style, just interesting to watch.

JBikes
JBikes
15 days ago
Reply to  David

You may be assuming there was a trade off for its increased DH abilities compared to previous less DH oriented bikes.

I personally view very little about this bike as being a “gravity shuttle”. Bikes just got more capable across the spectrum

DefRyder
DefRyder
16 days ago

At first i thought someone was messing with a long travel Epic experiment. I preferred the sidearm design of the previous Stumpjumper as the new one looks more like a long-legged Epic.

I’m sure it rides great cuz it’s plastered with the “Specialized” logo and price tag.

tech9
tech9
15 days ago

If you like the new Stumpy, I hope you like wireless shifting too because there is no routing for a derailleur cable on this frame!”

I can read into this a couple of ways.

  1. obviously sram only which is no problems there since axs works well.
  2. since spesh and shimano have had close relationships in the the past maybe there’s finally about to be a wireless di2 mtb group released from shimano?

Hopefully bullet 2.

John
John
13 days ago

This bike is not even capable of running a cable?!? Insert trombone wah wahs here***

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