Tested: Specialized’s New Stumpjumper 15

Yep. There’s a new Stumpjumper in town and, this time, there’s just one. No Evo. No ST. No 6Fattie, and no aluminum version. “Just” a new Stumpjumper with a new shock technology, new silhouette, new geo, and a whole bunch of other “new” things.

We’ll dive into all that in a moment, to explain and discuss our way through it - and I’ve got things to say about how the bike rides, too, of course. But first, take a trip down memory lane in this piece about our history with the Stumpy.

Specialized Stumpjumper 15 in a Nutshell

• Travel: 145 mm (rear) 150 (front)
• Wheel Size: 29” or Mixed 29”/27.5”
• Size Tested: S4
• Head Tube Angle: 63-65.5°
• Bike Weight (S4, Expert): 32.13 lbs (14.57 kg)
• Partial build weight (complete bike without wheels, tires, rotors, or cassette): 20.5 lbs (9.29 kg)

What’s New?

This review has the potential to become problematically ponderous, so here’s a one sentence hit list: the new Specialized Stumpjumper 15 combines the old Stumpjumper and Stumpjumper Evo into one bike that does away with the asymmetric sidearm, uses a new shock technology called “Genie,” has very adjustable geometry, is available in carbon only, and doesn’t have routing for a cable-actuated rear-derailleur. We’ll dive into each one of those points in detail, but this is an all-new chassis, with all-new suspension, and a few details that are going to be quite controversial.

There’s a Genie in the Shock

No, that is not a typical air shock bolted to the new Stumpjumper. Instead, it uses a dual-positive-air-chamber tech that Specialized calls “Genie.” Specialized is no stranger to proprietary suspension products; from Autosag, to Brain, to that sweet dual crown fork on the old Enduro, the Big S has a strong history of getting a little weird with suspension. Genie is their latest rear shock tech, designed by Specialized, and brought to life by Fox.

Before we get into the nitty gritty of how this shock works, hold on to your outrage: the shock is proprietary, but the frame isn’t. Specialized says that the new Stumpjumper has a very smooth “normal” suspension curve that should work very well with most air and coil sprung shocks on the market. If you don’t like Genie, you can bolt on another 210x55 mm stroke shock and go on with your life. I’ll wrangle up another shock or two to swap onto this Stumpjumper, but for now, Genie works really, really well.

How does it work though? Well, inside that bulbous shock, you’ve got a pretty normal Fox Float damper. The difference lies in the air chamber(s). Specialized set their sights on creating a suspension product that’s really supple and reactive in the initial portion of the stroke. The best way to achieve that was by increasing the volume of the positive air chamber. That allows the shock to react more to smaller bumps, maintaining traction, and smoothing out the ride.

But a super reactive, supple shock is all well and good until you hit a bigger compression, or try to load the bike to pop or pump. That’s when you need the shock to ramp up to a firmer platform in the end stroke. So Specialized settled on a design that uses two separate but connected positive air chambers. For the first 70% of the stroke, you’re compressing both chambers, so you’ve got a bunch of air volume to work with, and the shock feels impressively smooth and reacts to every bump really easily. But, when the shock hits that 70% mark, it closes off the ports to the outer chamber, and effectively becomes much lower volume, for a much more aggressive ramp up in that last 30% of the stroke. That prevents harsh bottom outs, and gives riders a consistent platform to push off.

I’ll be really candid here: I’m very skeptical of “revolutionary new suspension technologies” and there’s a healthy dose of “marketing talk” integrated into the presentation on Genie that I watched before I rode the bike that rolled my eyes into a somewhat rearward position. But Genie isn’t actually that weird. Specialized says that there’s only one additional seal required to service a Genie shock over a typical Fox Float, and that any suspension facility that can handle a Float rebuild can handle a Genie rebuild. And again, don’t like Genie? That’s fine, you can run whatever other shock you’d like!

I’ll talk about how the Genie shock on this bike feels lower down (short version: great and pretty normal), but there are a few other things to note: You can independently tune the volume of both chambers with included spacers to adjust the initial stroke and ramp to your liking. You set the sag of the Genie shock just like you would any other, and Specialized is bringing back their suspension calculator for this new Stumpjumper.

Specialized says that they did a bunch of testing and came to the conclusion that the Genie shock on this Stumpjumper wouldn’t see massive performance benefits from incorporating an external oil reservoir, but it will be interesting to see if it starts to pop up on other Specialized models.

Finally: A note on mid-stroke support and hydraulic bottom out. My initial worry when I skimmed through the Genie presentation was that this all sounded great for the first third, and last third of a bike’s travel, but what about that mid-stroke? Specialized says that they’ve found that what most riders think of and feel as “mid-stroke support” in the rear end of a bike isn’t actually coming at the middle of the shock’s stroke. Instead, it’s happening closer to the middle of the bike’s travel between sag and bottom out, which, not coincidentally, is where the extra chamber of the Genie shock closes off and things start to ramp up and get much more progressive.

And while a few brands have been bringing hydraulic bottom out circuits to their shocks, Specialized says that the Genie performs significantly differently. They characterize the difference as one of performance vs comfort: HBO softens the impact of a hard bottom out, and makes it feel less abrupt and violent, while Genie should do much more to mitigate the possibility of it even happening.

Frame Details

The new Stumpjumper delivers all the considerate detail we’d expect from Specialized. The new SWAT 4.0 system that we saw on the Epic and Epic Evo is implemented on this bike as well. It’s excellent, easy to use, with decent waterproofing and great ergonomics.

The new Stumpjumper frame doesn’t have the asymmetrical diagonal sidearm of previous models. Instead, Specialized says they took the carbon used there and distributed it in other portions of the frame to create a lighter frame that still hits their stiffness parameters.

Most sizes of the Stumpjumper are compatible with both 29” and 27.5 rear wheels, but S1 and S2 bikes are 27.5 rear only, while S3-6 can swap a suspension link to account for different wheel sizes. All air-sprung bikes come with full 29” wheels by default and Grid Trail casing tires, while the coil sprung builds come with 27.5” rear wheels, 160 mm 38 mm stanchion forks, and Grid Gravity tires.

The Stumpjumper uses a 34.9 mm seat post and 200 mm post mount interface on the rear end, both of which I quite enjoy.

All of the new Stumpjumper frames also get lifetime bearing replacements for the original owner, and come with slick integrated fenders on the main pivot. They come with easy-to-route internal slots for the dropper post and rear brake, but not, importantly, for a rear derailleur.

A Charged Decision

Yep. That’s right. The new carbon Stumpjumper is only compatible with wireless drivetrains. No Shimano for you unless you want to use Archer’s wireless solution, or run wires from your Di2 e-bike drivetrain to a battery jerry-rigged into your SWAT box. No cables, unless you want to take an afternoon to figure out an externally routed solution for your superbike. This is something of a BFD (big fucking deal). It’s the sort of thing the doomsday retrogrouches have predicted for ages, and I’m somewhat bummed to see it happen, just because it proves them right. We’ll have a more in-depth piece discussing this decision soon. For now, it is what it is.

I’m on the record as really liking Sram’s new Transmission (although I’m dealing with some frustrating issues that I’ll detail in an upcoming piece.) All builds of the new Stumpjumper come with some form of Transmission and, conveniently, SRAM is releasing their newest, most affordable build of Transmission, S1000, today. It’s OEM only, and uses a two-piece cassette that mounts to a regular HG driver, not the XD driver body that other Transmission cassettes require. We'll have more info on weights and performance soon, but on paper, it looks like a natural evolution for Transmission, although I’m sure I’m not alone in wishing it was driven by a cable not a battery.

Specialized says they eliminated derailleur cable routing because of market forces. Apparently, the sort of folks who buy carbon Stumpjumpers are not the sort of folks who want to put cable-actuated drivetrains on those bikes. It also saves weight (and expense) to eliminate that cable.

This decision opens a whole cannery’s worth of packaged worms. If we had comments, I’m sure you’d flock to them to let us know how you feel. Since we don’t quite yet, feel free to email me with your feelings. If they’re articulate, we’d love to run them. Is no derailleur cable routing better than running everything through the headset? Does anyone who’s actually in the market for a carbon Stumpy actually care about this decision or is it just us rabble rousers on the internet?

Anecdotally, in conversation with another large mountain bike brand (that’s not killing any cables), they mentioned that they’re eliminating their low-end complete carbon builds, and replacing them with high-end aluminum options because folks just aren’t buying anything below that GX Transmission trim when they’re shopping for a carbon bike. Market forces seem to be forcing markets in this direction.

Geometry

The Stumpjumper Evo has long been one of the most “modular” bikes around, thanks to the adjustability built into its flip chips and headset, and the new Stumpjumper continues that trend. The head tube angle can adjust down to 63° or up to 65.5° from the stock 64.5° with an included eccentric headset cup.

There’s another chip on the chainstays that adjusts the BB height by 7 mm, as well as adjusting the head tube angle by an additional .5° and changing the length of the rear center. That, combined with the link to swap wheel sizes, leaves riders with a dizzying array of options. But those options are all centered around pretty “normal” geometry. There’s nothing wild here, no dimensions that really stand out as envelope-pushing. I rode an S4 (I’ve been riding S4 Specializeds for a while) and this one fits my 6’2” frame well.

Just for fun, I made this chart comparing the new Stumpjumper to the old Evo and regular version of the same bike, as well as the average of the two. Based on those numbers, the new Stumpjumper is a touch more “Evo” than it is “regular.” The one number that’s changed the most is stack height: the new bike is 5 mm taller than the old Evo and 13 mm taller than the old Stumpjumper. My creaky back thanks you, Specialized!

Build Options and Price

The new Stumpjumper 15 is available in five different complete builds or as an S-Works frame only. All builds come with the same carbon frame.

The Stumpjumper Comp build retails for $5,500 and comes with Fox Performance level suspension and SRAM’s new S1000 groupset along with their Maven Bronze brakes.

The Stumpjumper Expert I’ve been riding comes with Performance Elite suspension, Maven Bronze brakes, and a GX Transmission drivetrain for $6,500

The Öhlins Coil version comes with, you guessed it, a coil sprung Öhlins TTX 22M shock and RFX38 M.2 fork, 27.5” rear wheel, TRP DH-R Evo brakes, and GX Transmission for $8,500.

The Pro build retails for $9,000, and is specced with Fox Factory suspension, SRAM XO Transmission, Maven Silver brakes, and Roval’s Traverse SL carbon wheels laced to I9 1/1 hubs.

The S-Works build gets a carbon link in the rear end to save weight, comes with Factory level suspension, an XX SL Transmission, Maven Ultimate brakes, Traverse SL rims laced to DT 240 hubs, and retails for an unsurprising $12,000. As a side note, it’s kind of wild to see the Maven Ultimate/XX SL Transmission on the same spec sheet. Specialized is combining SRAM’s DH race brake with their XC race drivetrain on their trail bike, which says something about their intentions for the Stumpjumper.

Finally, you can get an S-Works frame only with shock for $3,500.

Those prices are similar but a touch higher than the last generation of the Stumpjumper Evo - the new Comp build costs $100 more, but comes with a wireless drivetrain. The new Expert costs $200 more, the Pro is $100 more, and the carbon frame-only is $100 more.

I’ve been riding the Expert build, and I quite like it. Specialized’s tires are still really good, as are their house-brand components. The PNW dropper post is a nice touch. GX Transmission is still delightful, and the Maven Bronze brakes specced on the Stumpjumper are really great. They have me rethinking my words of caution in my original Maven review . Maybe they aren’t overkill on a trail bike? I know for sure that I’d take them over Codes on a bike like the Stumpjumper every time, and the Bronze level Mavens are so much better than any “R” level SRAM brake I’ve used in the past. I love these brakes.

First Impressions

I’ll follow up with a full review eventually, but here’s some first impressions: so far the new Stumpjumper 15 is a very easy to appreciate bike. It was easy to set up to the recommended 16 mm of sag at the shock, it’s easy to pedal uphill, and it’s easy to rally back down.

I’ve been riding the Stumpjumper in its stock “high” and “neutral” positions so far, but I’ll experiment with other extremes in the future. As-is, it feels really balanced and fun to ride on a variety of trails. It pedals well without touching the lockout lever and is fairly light given the burly build.

On the way down, it’s even-keeled and predictable. I really like how the Genie shock rides. I think in a blind test, I would guess this bike was coil-sprung and very progressive. It has excellent traction and erases small bumps with aplomb. I have weak, sore ankles, and I notice them working less hard and feeling less beat up after rides than on my STEEZL, but I’ll be swapping around shocks to dive deeper into that soon. I have also been struggling a little to match my fork setup to the rear - it’s so supple, so smooth, and it makes me crave the same sensation up front - so I’ll be adding some volume spacers and experimenting there too.

For now, the Stumpjumper 15 is a hoot. It’s super easy to get along with and feels nice and well-rounded.This is just the beginning, though: Specialized has designed it to be super versatile and adaptable and I’m excited to play with those options in the coming weeks.