The year marks the redesign of the Specialized Stumpjumper, a bike that has been on the trails since 1981. Specialized checks off every single box with this bike, underlines a few, and adds some of their own. Three build levels are available, and 27.5 and 29 wheel sizes are offered for all variants. In the lead-up to this launch, Specialized provided Mtbr an all-access pass to their engineers so we could dive deep and geek out about the what’s and why’s of the redesigned Stumpjumper.
Before delving into specifics, a general model overview is needed. As mentioned, three versions are available: standard travel, short travel (replacing the Camber), and EVO. Specialized uses the phrases: fast and planted, snappy and nimble, and gravity-focused to describe each of these versions. Both wheel sizes are available for all models, there are carbon and alloy frames, and various component options, too. The standard and short travel versions are available at local dealers now. Pricing info is below.
How do they differ? It’s actually simple. Short travel models have the same frame as standard travel, but a different shock, shock extension, and fork. They also come equipped with 2.3 tires instead of the 2.6s on all the others. Key standard travel measures are: 29er 150mm/140mm front and rear travel; 27.5 150mm/150mm f/r. Short travel comes in at 130mm/120mm f/r for 29er, and 130mm/130mm f/r for 27.5. And yes, Specialized has finally adopted the 27.5 nomenclature. No more 650b.
The list is long. Gone are symmetry and flex, arriving is the sidearm and threaded bottom bracket. Returning is a chainstay bridge and remaining is SWAT. The list continues with a new dropper post, reengineered chainstay protector and improved cable routing.
During development, significant time was spent equating and optimizing the feel of rider contact points using both computer simulations and saddle time. Mountain specific stiffness metrics were developed, rather than simply reusing optimal from road. The Stumpjumper’s geometry has also been revised, relaxing certain angles, steepening others, and stretching things out.
The Specialized engineers started from the simulation-based stiffness numbers, tested them on the trail, then overwrapped the frames with additional material and sent their riders back out. This was repeated to see what the additional material actually felt like while riding. Some numbers might change by tiny percentages in the lab, but equate to a large difference in feel. One notable area where they wanted to improve was tracking through chattery corners.
After extensive testing they arrived at a balance point, where additional material did not improve stiffness, preventing unnecessary additional weight. The end result, comparing medium 2017 Comp Carbon frame vs. 2018 Comp Carbon: 2018 is 550g lighter. The newer Comp frame now includes a carbon rear triangle, so an apples-to-apples comparison would be S-Works all carbon, which resulted in a weight reduction of about 250g versus the 2017 model.
The rear end of the new frame is 8% stiffer than the previous generation, claims Specialized. And the new frame itself is 20% more efficient, without accounting for optimizations in layup and construction. These efforts have an additional perk – SWAT storage is now 20% larger.
A contributing factor to increased lateral stiffness is the sidearm. This appears to add a common practice from roll cage design: triangulation, which significantly increases package stiffness. Adding the sidearm ties the three mounting points together: shock to frame, linkage to shock extension, and linkage to frame.
The shock is mounted off-center to the non-drive side, using an offset extension to attach to the seat stays. During the design process, forces acting upon every single bearing were analyzed and parts specified appropriately, resulting a significantly larger, stronger, and more durable main bearing pivot bearing, said Specialized.
Both Standard and Short Travel Stumpjumpers share the same frame, yet geo numbers are slightly different due to the bike’s static position. Notable items for 29er are 66.5-degree head tube angle, 437mm chainstays, moderate reach at 445mm (Large), 641mm of stack (Large), 74.1-degree seat tube angle, and 342mm BB height. The 27.5 version is slightly slacker with a 65.5-degree head angle, 432mm chainstays, 455mm reach (Large), 623mm stack (Large), 74.6 degree seat tube angle and ground scraping 432mm BB height. These geo numbers vs. wheel size is a nice alignment with typical riding styles.
The 29er version of this frame remains compatible with 27.5+ tires, and both frames are claimed to accommodate up to a 3.0 tire in the back, while maximum width up front is determined by the fork. All frames have boost hub spacing.
Specialized incorporated geometry adjustment into the shock eyelet’s flip chip (a standard eyelet metric shock is now used), which lets the rider change the headtube angle by 0.5 degrees and BB height by 6mm.
The EVO build is available in alloy, two wheel sizes, and two frame sizes for each, S2 and S3. Basically, just choose your reach. Seat tubes are incredibly short, so rider height should not impact it. These bikes will be available around June. We’ll have more info closer to that time. Travel is identical to the standard travel bike, just using different geometry.
Specialized spent significant time working with both Fox and RockShox during the Stumpjumper’s development, merging frame kinematics with spring curve to optimize the wheel forces. The end result is a fairly linear force progression through the travel. The 2018 frame’s leverage ratio goes from ~3.0 to ~2.6 as it progresses through its travel.
Some bike models have a women’s specific version, which also include a Women’s Trail RX Tune that’s optimized for lighter riders. If a rider wants the frame-only version (not women’s specific bike), the shock can be tuned to the Women’s RX specifications, which mostly involves a less progressive air spring, a user or shop serviceable item. Gone are Ohlins suspension and auto-sag functionality.
The EVO has a similar damper and damper tune to the other bike models, but the air spring has been modified. Goals for EVO are excellent small bump performance and descending capability while maintaining big hit performance. So it has a more powerful negative air spring (for small bumps) with more progressive positive spring (for full travel support).
After an exhaustive optimization process, Specialized wanted to ensure customers can still make the bike match personal preferences and riding style demands. As such, the stock air springs target the midpoint of adjustment. If you want more ramp-up, add spacers, if you want less, remove some. If you want to run a coil, the frame works well with that, too. Does it void the warranty? Nope. But the user is expected to ensure clearances and match OE specified eye-to-eye and stroke. The point is, Specialized attempted to maximize user customization.
During our brief test period Mtbr had the opportunity to compare weights on a few models. These numbers are less about absolutes and more about relative comparison. All bikes were setup tubeless (no idea about sealant quantity in each), without pedals, with empty SWAT pockets:
The Command Post has finally been updated and now has 160mm of drop, 16 positions, reduced top-out force, and increased stiffness with a 34.9mm seat tube.
2018 Specialized Command Post dropper actuation.
Two improvements have been made around the chain. The chainstay protector has been rethought and retitled. It’s now called the Chain Silencer. Instead of padding for a great big slap, Specialized added some filtering to soften the motion prior to stopping it, resulting in a very quiet ride and improved frame protection.
The upper chain guide has also been redesigned, adding strength and retention capability plus the convenience of tool-free chain removal.
Most modern frames have internal cabling. Some are easier to route than others. I’ve not seen any that are as easy as what this Stumpjumper has. From entry to exit, the routes are fully enclosed, even transitioning between the frame and the chainstays. It’s a total enclosure on both the carbon and alloy frames. Yes, you’ll need to open your brake line when installing new brakes, but properly installing them means cutting the line to length anyway.
Through redesigning the frame, stiffness increased, but the frame walls actually moved outward and became thinner so additional volume is available for the SWAT pocket. Specialized also removed the bezel that used to protrude. The door now attaches directly to the frame, and a full size water bottle still fits.
Bottom line, in Mtbr’s opinion the 2018 Stumpjumper addresses all rider requests we’ve heard, pushing beyond those minimums to create the bike both Specialized’s riders and designers want. It appears to be a daily do-it-all bike with few limitations, making rides easier and more enjoyable. After learning all of the information provided above, we had three days to ride the trails around Ainsa, Spain, to see for ourselves how it rode.