The Specialized Stumpjumper FSR 6Fattie pushes the evolution a step further by introducing the plus sized wheel and tyre format to this iconic model. Our long term test bike is the Specialized Stumpjumper FSR Expert Carbon 6Fattie.

The build

Looking at the Stumpjumper FSR range as a whole it fits firmly in the trail bike category, offering 135 to 150 millimeters of rear travel depending on the wheel size. It is available in standard 650b, 29 inch and 650b+ or “6Fattie” versions, with the standard 650b the only of the three sporting the 150 millimetres of travel in the rear.

The Stumpjumper FSR Expert Carbon 6Fattie features a carbon front triangle with an alloy rear end. As you move further up the price tiers that M5 alloy rear is swapped out for carbon. The carbon chassis includes the Specialized SWAT door for ultra-convenient storage of your spare tube and a few tools within the down tube. It’s an ingenious use of space to free up pockets, backpacks or rid your bike of that awkward saddle bag.



The Expert Carbon 6Fattie has a rock solid component lineup, arguably heroed by the RockShox Pike RC 29/27.5+ providing 150 millimeters of dependable travel up front. At the rear, a RockShox Monarch RT3 sporting AUTOSAG supplies 135 millimeters of travel. The wheels comprise of Roval Traverse 650 alloy rims laced to Roval hubs front and rear, in Boost 110 millimeter and Boost 148 millimeter sizing respectively. The rims are wrapped in the voluminous Specialized Purgatory GRID 3.0 tyres.

A mash-up of SRAM GX shifters, a SRAM X1 rear derailleur, and RaceFace Aeffect crankset provide a dependable no-nonsense drivetrain that won’t require a re-mortgage to replace. No doubt many will be asking “but what about Eagle?”. For 2018, the Expert Stumpjumper is equipped with SRAM Eagle GX while the Comp model still sports eleven-speed GX. SRAM Guide R brake levers paired with Guide S4 4-piston calipers provide ample stopping power.





Rounding out the build, the cockpit and contact points are all catered for in-house. A Specialized Trail alloy bar and stem combo make for a suitably wide and short cockpit with 750 millimeter bars bolted to a 60mm stem. The Specialized Command Post dropper and Specialized Henge Comp 143mm saddle creates a comfortable perch with a 12-position adjustment through 125mm of dropper post travel.

It’s worth noting that the 29 inch and 6Fattie variants are identical in their geometry. Swop out the 650b+ wheels for a set of boost 29” hoops and we’re rolling on a Stumpjumper FSR Expert Carbon 29.

Stumpjumper FSR Expert Carbon 6Fattie specifications

  • FrameFull Carbon Front Triangle, Full CaFACT 9m, carbon front chassis, M5 alloy rear end, Trail Geometry, SWAT Door integration, PF30 BB, fully enclosed internal cable routing, ManFu link, 12x148mm dropouts, sealed cartridge bearing pivots, replaceable derailleur hanger, 135mm of travel
  • ForkRockShox Pike RC 29/27.5+, Solo Air, compression and rebound adjust, tapered steerer, 15x110mm Maxle Stealth thru-axle, 51mm offset, 150mm travel
  • Rear ShockRockShox Monarch RT3, Rx Trail Tune, AUTOSAG, rebound and 3-position compression adjust, 197x48mm
  • CranksetRaceFace Aeffect, 6000-series alloy, 24mm spindle, 52mm chainline, 28T
  • Bottom BracketShimano BB-MT800 Pressfit
  • Front DerailleurN/A
  • Rear DerailleurSRAM X1 Type 2.1, 11-speed
  • ShifterSRAM GX, 11-speed, trigger
  • Front BrakeSRAM Guide R, hydraulic disc, organic pads, Guide S4 4-piston caliper, 200/180mm rotor
  • Rear BrakeSRAM Guide R, hydraulic disc, organic pads, Guide S4 4-piston caliper, 180/160mm rotor
  • CassetteSRAM XG-1150, 11-speed, 10-42t
  • ChainSRAM PC-1110, 11-speed w/PowerLink
  • PedalsN/A
  • RimsRoval Traverse 650, hookless alloy, 29mm inner width, 24/28h, tubeless ready
  • SpokesDT Swiss Revolution
  • Front HubRoval Traverse, sealed cartridge bearings, 15mm thru-axle, 110mm spacing, 24h
  • Rear HubRoval Traverse, DT Swiss internals, sealed cartridge bearings, SRAM XD driver body, 12mm thru-axle, 148mm spacing, 28h
  • TiresPurgatory, GRID casing, 650bx3.0", 60TPI, Aramid folding bead, 2Bliss Ready
  • HandlebarsSpecialized Trail, 7050 alloy, 8-degree backsweep, 6-degree upsweep, 25mm rise, 750mm width, 31.8mm
  • GripsSpecialized Sip Grip, half-waffle, S/M: regular thickness, L/XL: XL thickness
  • StemSpecialized Trail, 3D forged alloy, 4-bolt, 6-degree rise
  • SeatpostCommand Post IRcc, 12 position micro-height adjustable, alien head design, bottom mount cable routing, remote SRL lever, 30.9mm, S: 100mm, M/L/XL: 125mm travel
  • SaddleBody Geometry Henge Comp, hollow Cr-Mo rails, 143mm

On the trail

There are a certain set of expectations created when you mention anything plus or quasi-fat in mountain bike terms. Bigger tyres usually mean stability, better traction and improved capability, but often at the expense of weight, precision and feel. While Plus size in general is intended to hit the sweet spot between fat and standard, delivering the best of both, we were curious to see how the 6Fattie would fare.



On its very first outing at my trusty local Tokai trails, the Stumpjumper 6Fattie delivered smiles in spades and shattered some of my early expectations. As a trail bike, it naturally excelled on the twisty technical stuff and, if Strava PRs were a measure of a bike’s worth, the fistful of new PRs served as an early indicator that this is a goodie. I quickly found a new excitement for trails and I was instantly able to shave seconds off and comfortably sail through technical switchbacks that I’d usually awkwardly fumble.

I had anticipated lumbering climbs up thanks to the “bigger boned” construction and trail geometry. At 13.85 kilograms sans pedals this particular 6Fattie is not all too heavy as far as trail bikes go, especially considering the mid-range build and alloy rear end, not to mention the plus tyres. The distinctly upright and comfortable riding position along with generous gearing make for easy climbing. You do feel the bulkier tyres on the ups and flats, but the added stability and traction over uneven terrain largely offsets any losses from rolling resistance and mass.

At slower speeds through flat, obstacle-laden singletrack the broader tyres provide a very forgiving ride. You’re able to roll over roots or rocks with greater ease and the tyres hang onto every bit of grip they can find. The added stability also helps in slow speed, technical turns and switchbacks. I did struggle with frequent pedal strikes initially due to the relatively low bottom bracket, but after a few rides I gained a better sense of the limits.

As the trails point down you immediately feel that the bike wants to go. The rolling mass of the tyres create a sensation of speed and although not the quickest to accelerate, once going the bike carries momentum well. It stops promptly too thanks to the larger contact patch and 4-piston calipers. At higher speeds, the tyre pressure does become critical to the performance and needs to be carefully matched to the terrain and rider. Set the tyre pressure too hard and the bike behaves more like a pinball through rock gardens, but too soft on hard packed flowy surfaces and you’ll note a definite wafty squish through berms. There’s a bit of a goldilocks approach to getting this just right and after some trial and error at both extremes, I soon found the sweet spot for my weight and riding conditions. It will vary based on your weight and trail conditions, but at 75kg I found a range of 16 to 18psi to work well, with the front on the lower end and rear higher end of that range.

One of the biggest pluses for me was the boost to my confidence on the trail. I don’t proclaim to be a hardened trail shredder, but the 6Fattie had me biting at features I’d usually chicken run and pointing down lines I wouldn’t typically dare. As I grew more comfortable with the bike’s capabilities I pushed it (and myself) that bit further. The only downside was that this new found faux confidence was carried over to other less forgiving bikes at the expense of some skin and dignity. While it’s by no means a replacement for skills, the 6Fattie does add a layer of confidence thanks to its impressive stability.

Towards the latter part of the testing, I had the opportunity to try the Stumpjumper 6Fattie out in 29er mode. With some loaner cSixx Carbon hoops the Stumpy shed some rubber and weight. With some “normal” tyres there was a definite improvement in the responsiveness thanks to the lighter wheels and tyres. Additionally, the tyre pressure sensitivity I’d experienced with the 6Fattie tyres was now a non-issue. Overall it felt good, but after a couple of rides, I was somehow left underwhelmed. At the time I couldn’t quite put my finger on what I didn’t love about the 29ers, but in reviewing what I enjoyed about the plus format it was obvious. Reverting back to skinnier tyres took the security and dependability I’d come to expect away, and with it, my new found confidence fizzled. Suddenly I was jittery, unsure and uneasy. There is a tradeoff in ride feel with the fatter tires which can be a bit vague and the more technically adept may prefer the distinct feedback from slimmer tyres. For me it was that “throw me at anything” factor of the 6Fattie which produced the smiles.




All considered the Specialized Stumpjumper FSR 6Fattie is an incredibly fun and rewarding bike to ride. For a newbie to mid-level rider seeking a playful and confidence giving trail bike the 6Fattie is well worth a test ride. More experienced riders may favour more precision and steer away from the 6Fattie option in favour of the 29” or 650b.