Specialized's new Stumpjumper 15 grants trail riders all their wishes, thanks to the Genie dual-stage air spring.

Product Overview

Specialized Stumpjumper 15 Pro Carbon


  • * Next level tuning possibilities with Genie shock tech
  • * Better overall suspension that the Stumpy Evo
  • * Lightweight but solid sub 14kg build
  • * Custom tuned Fox 36 fork feels amazing
  • * Still pedals like stink


  • * Rear tyre needs more sidewall support
  • * Cheapest option is currently £6k
  • * Coil sprung Ohlins option adds confusion


I’ve tested every generation of Specialized’s full suspension Stumpjumper, and the latest version with the Genie shock tech is the best yet 


Price as reviewed:


Specialized’s Stumpjumper Evo is without doubt, one of the best mountain bikes on the market. And I’m not just throwing that statement out there lightly… the Stumpy Evo has the test results to back it up. The carbon version took the top spot in our 2022 Trail Bike of the Year test, and more recently, the alloy Stumpy Evo won our Adjustable Trail Bike shootout. One of the most Decorated trail bikes ever made? You bet. And it’s not just MBR that sings it praises, the Stumpy Evo is universally regarded as the benchmark trail bike.

So how do you improve upon such an accomplished ride? What you don’t do is throw the baby out with the bath water. So while Specialized has dropped the EVO tag, the funky side-arm frame layout, and a bit of travel with this latest version, the fundamental shape and attitude of the bike remains unchanged. And having spent four days on the new Stumpjumper 15 Pro Carbon I’m convinced it’s the best version yet, and better than the old Evo bike it replaces. And it’s the changes to the suspension layout and the new Genie shock technology that elevate the overall ride quality to new heights. If you want to read the headline changes and check out the models and prices, read our news story on the Specialized Stumpjumper 15.

Specialized Stumpjumper 15 Pro

Specialized Stumpjumper 15 Pro looks set to define the next generation of trail bikes

Specialized Stumpjumper 15 Pro Carbon Need to know

  • 15th version of Stumpjumper replaces old Stumpjumper Evo
  • Rear travel is 145mm, down from 150mm
  • Fox Float shock with Genie dual-stage air spring tech for more adjustment
  • Custom tuned 150mm Fox 36 Grip X2 fork with lighter damping
  • Carbon frame and suspension layout mirror Levo SL
  • Same geometry adjust features as old Stumpy Evo
  • MX or full 29in wheels with dedicated shock links
  • SRAM X0 T-Type AXS drivetrain
  • New low-profile SWAT door, same storage capacity
  • Improved seat post insertion on smaller sizes
  • Six frame: sizes S1 to S6
  • Weight: 13.98kg (size S4 with SWAT)
  • Four carbon models with Genie tech: S-Works, Pro, Expert and Comp
  • One Ohlins model gets a 160mm fork and coil shock (EVO?)

Frame and geometry

Okay, so the most obvious change to the new Stumpy frame is that the distinctive side-arm, that ran parallel to the shock on the Stumpy Evo, is gone. And that shouldn’t come as a surprise, because one look at Specialized’s most recent trail bike, the Levo SL, says everything you need to know about the direction its design language is taking. In fact, the new Stumpy looks remarkably like the Levo SL, and the similarities extend to the suspension kinematics too. But I’m getting ahead of myself.

Specialized Stumpjumper 15 Pro

With no side-arm, the new Stumpjumper looks more like the Levo SL

Specialized claims that in bench tests, the new Stumpy frame sans-side-arm is every bit as stiff as the old design and isn’t any heavier. And, for a sub 14kg trail bike, the Stumpy 15 Pro Carbon that I rode certainly felt solid. So, I won’t be mourning the loss of the side-arm. Also if Specialized had kept it, you wouldn’t be able to see the custom shock as easily, right?

Specialized Stumpjumper 15 Pro

The new Stumpjumper gets the same geometry adjustments as the old Stumpjumper EVO

The new frame layout also sports similar sizing and geometry to the old Stumpy Evo. It even retains the same degree of adjustability, where the drop-in asymmetric upper headset cup gives you +/-1º of head angle adjustment, and flip-chips in the chainstay pivots tweak the BB height by 7mm and also impact the head angle. Yes, I’d still like to see the addition of the shock eyelet flip-chip found on the Levo SL for additional tweaking, but then I am a total tweaker.

Specialized Stumpjumper 15 Pro

Improved seat post insertion depth, means longer dropper posts on all Stumpjumpers

One major improvement to the overall frame layout is the increased seat-post insertion depth. With a sharp kink in the lower section of the seat tube, Specialized has been able to add longer drop seat posts to the smaller frame sizes, which means shorter riders can now get the drop they need, and make use of the flexibility of fit that Specialized’s S sizing was originally intended for.

Specialized Stumpjumper 15 Pro

29in or MX? Two different shock yokes accommodate both options

There are still a whopping six frame sizes to choose from and the new Stumpy also gets semi-proportional chainstay length. I say semi, as there are only two options: S1 to S4 all have 435mm stays, while S5 and S6 come with 445mm stays. I’m not really sure if Specialized is totally sold on longer stays though, as the uneven split is clearly skewed to the shorter end. Different shock yokes are used to convert between 29in or 27.5in rear wheels, where the S1 and S2 ship stock in an MX format, and the four larger sizes are all full 29in.

Specialized Stumpjumper 15 Pro

New low-profile SWAT door on latest Stumpjumper is easier to open

One final change on the 2025 Stumpy frame is the new SWAT door. It has a lower profile than before, and has a glove friendly, easy-to-use lever to crack it open. All while retaining its industry leading internal storage capacity.


It’s what Specialized has done with the suspension on the new Stumpy that’s really interesting. The old Stumpy Evo had 150mm travel, the new non-Evo Stumpy has 145mm travel. Also fork travel has been chipped back from 160mm to 150mm on the air-sprung bikes. So nothing really to write home about here.

Specialized Stumpjumper 15 Pro

Specialized has gone with less anti-squat and progression on the 145mm travel Stumpjumper

Specialized has also tweaked the leverage rate and the anti-squat, making the FSR suspension on the new Stumpy less progressive while also reducing the amount of anti-squat. Again, these two subtle changes bring the Stumpy inline with Specialized’s current thinking on suspension behaviour, and the current Levo SL.

Specialized Stumpjumper 15 Pro

Inside the Genie shock. Genie Band closes outer air sleeve at 70% travel

So far, nothing out of the ordinary. Now let’s take a closer look at the inline Fox Float shock. At first glance the air-can looks massive, and it is. This is a seriously high-volume inline shock. It’s what’s under the air-can that makes it special though. By using a two-stage air spring, you get all of the extra air volume for the first 70% of shock stroke for a coil-like feel, then an alloy sleeve, dubbed the Genie Band, that’s attached to the main piston, cuts off the ports to the outer air sleeve, leaving the small volume in the head of the shock to provide all of the necessary end-stroke ramp up.

Specialized Stumpjumper 15 Pro

Under the top tube you still have compression and rebound adjustment

And, unlike a hydraulic bottom out, the end-stroke air spring is scaled and specific to rider weight, because it depends on the initial pressure in the shock needed to achieve the appropriate amount of sag. Neat, right? Also, given that the Genie air-spring tech only requires a few additional parts, the shock shares most of its architecture with the stock Fox Float, so it isn’t some crazy expensive proprietary tech that no service centre is going to touch. Also with so few additional parts, it should in theory be every bit as reliable as the stock Fox shock.

Specialized Stumpjumper 15 Pro

All of the steps in the development of the Genie shock

Best of all, the Genie tech allows the rider to easily tune the mid-stroke spring progression and the end stroke ramp independently of each other. Volume bands in the outer sleeve of the air-can adjust the mid-stroke, while volume spacers in the eyelet of the shock, just like on the regular Fox Float, adjust the end-stroke progression. So Specialized’s Genie tech brings a whole new level of tunability to the Stumpy suspension, much in the same way that all of the geometry adjustments on the Stumpy don’t lock you into a single philosophy on handling.

Specialized Stumpjumper 15 Pro

Custom tuned Fox 36 fork, does’t have Genie spring tech, at least not yet

And it’s not just the shock on the new Stumpy that has a unique twist. Specialized has made full use of the increased tunability that Fox is offering with the new Grip X2 damper cartridge to offer its own Rx tune on the 36 fork. I’ve not had a chance to ride the stock Fox 36 Grip X2 yet, so I have nothing to compare Specialized’s custom tune to, but the lighter damping felt very smooth and active on the Stumpy and should give lighter riders a more usable range of damping adjustment.  It also felt really balanced with the rear suspension.


It’s 2025, at least in bike years, so the Stumpy 15 Pro Carbon gets all the mod cons. SRAM AXS T-Type transmission, check. SRAM Maven brakes with Stealth levers, check. Bike Yoke 185mm dropper post, check.

Specialized Stumpjumper 15 Pro

SRAM Maven brakes have stacks of power, but can be tricky to modulate

It even has the new lower profile carbon Traverse SL II wheels. And the tech team at Specialized assured me that the new rims will make it much easier to get the tyres on and off than with the current carbon Roval hoops.

Specialized Stumpjumper 15 Pro

New lower-profile Roval Traverse II carbon rims are designed to reduce punctures

The Stumpy 15 Pro Carbon rolls on a Specialized Butcher/Eliminator tyre combo and both tyres use the Grid Trail casing. Up front, you get the softer T9 rubber for improved grip, while the rear tyre uses a harder T7 compound for faster rolling and reduced drag when pedalling.

Specialized Stumpjumper 15 Pro

We’d probably eliminate the Eliminator rear tyre, or go with a stiffer casing

Which kinda makes sense on a trail bike, at least until you start pushing hard. Because once you get the Stumpy up to speed, it feels like the rear tyre could step out at any moment.


It’s no secret that I really liked the old Stumpy Evo. But if I had one criticism of that bike, it would be that the suspension had too much of a pedalling bias, at least for a trail bike with such progressive geometry. As such, you’d take a bit of a beating on longer, rougher trails, even if it meant pedalling to the top of those trails was relatively pain free.

Specialized Stumpjumper 15 Pro

Primed and ready to roll: Specialized’s Stumpjumper 15 Pro is sleek

With the new Stumpy, Specialized has addressed my single criticism, and I’d even argue that it is more capable and adaptable than the old bike, even though it has slightly less travel and pedals just as well.


Two things immediately struck me as I headed out on the Stumpy 15 Pro and up the very first climb. It pedals just as effectively and as crisply as the old bike, but there’s also a subtle softness to the rear suspension that offers more traction than before. In that respect, it feels more like a coil shock albeit without the additional bobbing.

Specialized Stumpjumper 15 Pro

More grip on the climbs, same pedalling efficiency

Okay, so it’s not a night and day difference, but when pedalling up and over roots it was less jarring and there wasn’t such an aggressive tug of war going on between the pedals and the suspension.

Specialized Stumpjumper 15 Pro

The steeper seat tube angle only helps when you’re sitting down

Specialized’s recommended sag also felt a little too soft for me, so initially I increased the compression damping on the Fox Float shock to compensate, before adding more air. With the firmer setup I was still able to achieve full travel, but I had all of the support I needed for technical climbing, without ever feeling the need to reach for the climb switch on the shock. I was running just one of four red volume bands in the outer air sleeve, so a very linear setup, but not wallowy at all.


Open up the taps, and the new Stumpy quickly finds flow. And that support that was present when winching up climbs is still evident when loading the bike mid turn. Smash into a bump however, and the rear wheel gets up and over it with gusto. In that respect, you could argue that the new Stumpy feels like it has more travel than the claimed 145mm. It clearly hasn’t. But it still feels that way, because it uses the available travel so much more effectively. Basically, it’s not hitting a wall in the air-spring progression at the same time as there’s a sudden spike in compression damping.

Specialized Stumpjumper 15 Pro

With the more linear rear suspension set-up the new Stumpjumper rips through chunk

With a low level of mid-stroke spring progression (one red band) the rear suspension on the Stumpy would sometimes feel like it was falling through the travel a little too fast, especially if you drop your heels suddenly to pump the bike or when going deep off a drop, even though it never bottomed harshly. Now, I’m not saying this is a bad thing, it’s just very different to how the rear suspension on most other modern trail bikes behave. So, given the nature of the trails we were riding at the launch in Canada, effectively downhill pump tracks, I added two more red volume bands to the air-sleeve to increase the mid-stroke support and the transition between sag and full travel felt totally seamless.

Specialized Stumpjumper 15 Pro

That Eliminator rear tyre helps you get loose even when you’re not trying

Back home, I rode the new Stumpy 15 Pro Carbon on all my local trails, reverting back to the more linear setup (one red volume band). On rougher, natural trails, the rear suspension felt really effective. As a result, the bike seems to get pitched onto the fork much less and it’s almost scary how fast and recklessly you can ride this sub 14kg trail bike. It could also be why I seemed to ding the rear rim way more frequently than normal, but thanks to the “Flat Top” rim profile I’ve yet to get flat. I also think the sudden ramp in end-stroke support that the Genie shock offers could be causing the rear tyre to compress more rapidly at full travel, hence the rim dings. Then again, it could just be the thinner Grid Trail casing rear tyre not being up to scratch.

Specialized Stumpjumper 15 Pro

Poppy and playful, the Stumpjumper 15 Pro can do it all

And therein lies the real beauty of Specialized’s Genie dual-stage spring technology. You can adjust the end-stroke and mid-stroke spring progression independently of each other.  And because the engineering behind the Genie tech is elegantly simple, there’s no reason why Genie couldn’t be implemented on a Fox Float X2 or a RockShox Vivid Air for the next generation of Specialized Levo e-bikes and Enduros. Hopefully, Specialized will have figured out how to squeeze the Genie spring technology into a fork by then too.

Specialized Stumpjumper 15 Pro

The Stumpjumper 15 Pro is just the beginning for Specialized’s Genie shock tech


Specialized brought user-friendly geometry adjustments to trail riding with the Stumpy Evo. Now, with its new Genie dual-stage air-spring tech in the shock, it’s offering next-level suspension tuning possibilities that are just as easy to implement. Yes, the Evo tag, travel and side-arm frame layout have all been dropped, but the new Stumpy is lighter, every bit as stiff and is more capable than before. You also get better seat post insertion, updated SWAT storage, semi-proportional chainstays and a custom tuned fork. The best trail bike just got better, but this level of performance comes at a price. At £7,500 the Stumpjumper 15 Pro Carbon isn’t cheap. Even the entry-level Comp is £6K so the sooner Specialized launches an alloy version with Genie technology, the better.


Frame:FACT 11m carbon 
Frame travel :145mm
Shock :Fox Float Factory w/Genie
Fork :Fox 36 Factory Grip X2 Rx
Fork travel :150mm (44mm offset)
Hubs :Industry 9 1/1 110/148mm 
Rims :Roval Traverse SL II carbon
Front tyre :Butcher T9 Grid Trail 29x2.3in
Rear tyre :Eliminator T7 Grid Trail 29x2.3in
Chainset   :SRAM X0 Alloy, 32t, 170mm 
Shifter :SRAM X0 AXS
Derailleur :SRAM X0 T-Type AXS
Cassette: SRAM X0 10-51t
Chain :SRAM X0 Flat Top
Brakes :SRAM Maven Silver
Rotor :sizes 200/200mm
Handlebar:Roval Traverse SL Carbon 800mm
Stem :Industry 9 40mm
Seat post :Bike Yoke Revive Max 185mm 
Saddle :Bridge Expert
Weight :13.98kg (30.82lb)
Sizes: :S1 to S6
Size ridden:S4 (neutral/high)
Rider height:181cm
Head angle :64.5º
Seat angle  :69.8º
Effective SA :77º
BB height :337mm
Chainstay :435mm
Front centre :812mm
Wheelbase :1,247mm
Seat tube :425mm
Top tube :624mm
Reach :475mm
Stack :640mm