Back in July, Specialized announced the updated Stumpjumper 15 carbon – As of today, the alloy models have arrived. The Stumpjumper has always been a versatile trail bike, and its latest updates including increased rear travel, adjustable geometry, and new Genie rear shocks have affirmed its status as a top-tier ‘do anything’ trail bike.
Specialized has decided their carbon Stumpys should serve the higher-end market, while the alloy models offer lower-spec builds that come right down to entry-level prices. However, the alloy bikes get the same adjustable frame geometry and suspension kinematics as the pricier carbon models. Two of the complete builds also come with the new highly adjustable Genie rear shocks Specialized debuted with the carbon Stumpys.
Stumpjumper 15 Alloy – Frame Features:
The new Stumpjumper 15 Alloy frames are made from M5 Alloy. Like the carbon version, the alloy frame’s front end, rear end, and link were designed to ensure they work together to provide the amount of stiffness Specialized intended. Also like the carbon Stumpy, there is no longer a ‘sidearm’ on the alloy frame. Specialized realized they could reinforce the link instead, which offers a cleaner look at the same weight as the outgoing design.
The Stumpjumper 15 Alloy comes with 29” wheels on S3-S6 frames, and MX wheels on S1 and S2 frames… except the Fox Coil model, which runs MX wheels on all frame sizes. S2-S6 frame sizes are mullet compatible by adding aftermarket shock links which maintain the frame’s geometry and kinematics with the 27.5” rear wheel.
Six geometry settings are possible between the frame’s adjustable head angle and BB height, offering a wide range of tunability to suit different terrains or riding styles. The head angle is adjustable by swapping out the headset cups. Neutral cups come pre-installed, and +/- 1° cups are included with each bike. BB height is adjusted via a flip-chip at the rear end of the chainstays.
The updated Stumpjumper 15 Alloy frame does get Specialized’s SWAT down tube storage compartment. On the alloy Stumpys, the storage door is the same as the one found on the aluminum Stumpjumper EVOs. The new flush-mount door introduced on the carbon Stumpjumper 15 would not work due to a difference in tubing thickness. Specialized did say the volume of space inside is very similar to the carbon models. A zippered tool bag is included with each bike.
The alloy Stumpy frames get internal cable routing with entry ports on the down tube. Unlike the carbon version, the alloy frames get routing for a rear derailleur cable, so you’re not stuck with wireless drivetrains only!
Dropper post travel numbers vary as Specialized stocks different brands on different models, but rest assured all frame sizes offer enough room for ample length posts. For example, S2’s come stock with 150mm posts and S3s run 170mm posts. The Stumpy frame accepts 34.9mm posts.
The frames also leave plenty of space for water bottles. I reviewed the carbon Stumpjumper 15 Pro this summer and the S3 frame fit a large bottle easily. Side entry SWAT bottle cages are included on all models.
Other key fitments include Boost 148mm rear axle spacing, a 73mm threaded BB, and SRAM UDH-compatible dropouts. For frame protection, the bike includes chainstay/seatstay guards, and a lower down tube guard.
If you tend to keep bikes for the long haul you’ll be happy to hear Specialized now offers free lifetime replacement of all linkage pivot bearings to the original owner.
Suspension:
The Stumpjumper 15 alloy offers 145mm of rear travel driven by Specialized’s FSR linkage. Fork travel is 140mm on S1 frames, and 150mm on all others… except the Fox Coil model, which runs a 160mm fork on all frame sizes.
Specialized strove to ensure the new Stumpjumpers would offer great small-bump sensitivity, the lively ride you’d want from a mid-travel bike, and plenty of capability to absorb hard hits from rough terrain or big drops.
The Stumpy’s FSR linkage was tuned to require very little force to get into its mid-travel range. Compared to the Stumpjumper EVO, the new Stumpy will use 100mm of travel facing the same amount of impact force that would use 86 mm of the EVO’s travel. This initial softness aims to make the stumpy feel like it has more travel than it really does (and after riding the carbon version, I’d agree it does accomplish this). The tune also results in better bump-force management and significantly improved traction versus the Stumpy EVO.
To ensure excellent pedaling prowess, the Stumpy’s anti-squat was fine-tuned to sit right between the previous Stumpjumper and Stumpy Evo models.
Genie Rear Shocks:
Specialized’s new Genie-equipped Fox Float Performance rear shocks come on the Comp model and alloy frameset. They are not included on the Fox Coil model or the base ‘Alloy’ model. This is a good time to point out that while the Genie shock was developed alongside the Stumpjumper, the bike can run other rear shocks.
For a full rundown of the Genie shock technology, check out my Stumpjumper 15 carbon launch article. In short, here’s how it works: The shock features a unique outer air chamber, and Genie sleeves inside that slide back and forth as the shock compresses and expands. The outer air chamber remains open for the first 70% of travel, and with that added to the shock’s typical inner air chamber the extra volume can give the shock a highly sensitive, coil-like ride feel. However, the spring rate of the outer air chamber is tunable: By adding spacers to that chamber, you can reduce the overall air volume in the shock and produce a more supportive, lively ride.
What’s important to note is these adjustments only affect the first 70% of the shock’s travel. At 70%, the Genis spacers slide over a set of ports and close off the outer chamber. The last 30% of travel gets more progressive as the air volume in the shock is instantly reduced. Furthermore, the inner chamber’s shock rate is separately tunable using typical eyelet volume spacers.
Specialized has added an extra air volume chamber to the shock without using a piggyback or remote accessory, and they’ve made it so both bottom-out resistance and the mid-travel range you spend most of your time riding within can be tuned individually.
Geometry:
Stumpjumper 15 Alloy frames are available in sizes S1 – S6. The Stumpy Alloy’s geometry is exactly the same as the carbon models.
Please note: Due to the longer 160mm fork and 27.5” rear wheel on the Fox Coil model its geometry varies slightly from the other models, and it is not available in the S1 frame size. See Specialized’s website for the coil model’s geometry.
Specialized has taken the approach of keeping standover heights close across their frame size range, so riders can choose the reach that matches their riding style or preference. The Stumpjumper offers six sizes to choose your ideal reach from – The smallest S1 frame is 400mm, the largest S6 is 530mm, and the sizes in between grow by 25-30mm each.
There are four different chainstay lengths across the six frame sizes. The S3 and S4 frames share the same size, as do the S5/S6 frames. Specialized kept the rear ends on the shorter side, which I’d say is suitable for a ‘do everything’ trail bike.
The Stumpy’s head tube angles are adjustable from a super slack 63° to 65.5°, and the seat mast angles differ slightly by frame size but range from 76.5° to 78°. The BBs ride pretty low at 337mm in the High position or 330mm in the Low (except the S1 frame which sits 3mm lower).
Model Lineup:
The Stumpjumper 15 Alloy is available in three complete builds and as a frameset. If you drooled over the carbon Stumpys but found them a bit beyond your price range, you’ll be happy to see the much more attainable models in the alloy lineup. Check out Specialized’s website for complete build specs on each model.
- Stumpjumper 15 Fox Coil Alloy – $5,500
- Stumpjumper 15 Comp Alloy – $4,500
- Stumpjumper 15 Alloy – $3,000
- Stumpjumper 15 Alloy Frameset – $2,300
