2015 Specialized Stumpjumper FSR Comp Carbon 6Fattie

Suspension Setup

A few years ago, Specialized created a system intended to allow for easier rear suspension setup – they call it AutoSag. You pump up the rear shock to a really high pressure, sit on the bike, and press a release valve that lets air out of the shock until you hit the proper sag, then stops.

I love the idea. Shock setup is critical to bike performance, but can be challenging to get right if you aren’t experienced with it. This at least makes getting the right spring rate pretty easy.

But it isn’t all roses: the pressure release valve is very dependent on bike orientation. If you are on a slight incline or bounce on it a bit weird when releasing the air, you can get the wrong air pressure. However, it still provides a great baseline. I would often end up with the AutoSag set to 160 psi, but preferred 170. I ran 70 psi in the fork for most of my riding.

On the Trail: Going Up

Most of the trails around Park City offer smooth, well-graded climbs, but off the beaten path, there are plenty of rocky, gravel-y climbs that offer some challenge, and provide a great opportunity to test out a new bike. I sought out a favorite tight and loose neighborhood climb for my first ride test–then rode it again, and again after that. (It’s my neighborhood loop, after all.)

Unsurprisingly, the wide rear tire offered great traction. On the way up I never had a tire spin out, even when going over the loosest, rockiest bits of the trail.

I haven’t had a chance to get the Stumpjumper out on wet roots like one might find in the Northeast or the Northwest, but I suspect it will do reasonably well. The only hurdle I see to success on wet roots is the tire compound. It is listed as a 50/60a durometer – that is harder than most tires that excel in wet conditions.

More surprising to me on the climb was the Stumpjumper’s efficiency. The big tires did take a bit of energy to keep moving, but I never lost any energy spinning a tire. This may seem like a small thing, but when I had the opportunity to ride a 2,000 ft climb on entirely fresh (soft and loose) trail, it made a huge difference, and I comfortably put a gap ahead of my riding partners.

There is something of an inexorable, tank-like nature to climbing on the Stumpjumper. It doesn’t want to go fast, but it is a surprisingly pleasant bike to grind up a long climb on. It also helped that the suspension’s pedaling performance was great—good enough that I didn’t tend to use the lockout lever except on pavement. (This bike is very, very slow on pavement.)

On the Trail: Flats

When the trail gets flatter, the added traction is less helpful and the rolling resistance more noticeable. But the tires make up for it by holding speed pretty well, like a 29er. Only on pavement or really firm hardpack was the rolling speed really slow. Otherwise, the tires were pretty comparable to my usual 2.4 Highroller / 2.3 Minion combo in terms of rolling resistance. Not quick, but not all that slow, either.

The 3” Specialized tires paired with 29mm internal width rims give the tires a very rounded shape. That shape makes it handle like a 29er when upright, but as soon as you tip it over for a corner, it feels like 27.5 bike because you are leaning over onto the smaller diameter outside of the tire. That was pretty cool, and makes the handling a bit more responsive than a 29er. I didn’t feel myself fighting rotational inertia as much. However, the narrow rim also means that the tire is not very well supported, and can feel very squirmy.

Tom Collier reviews the Specialized Stumpjumper FSR Comp Carbon 6Fattie for Blister Gear Review.
Tom Collier on the Specialized Stumpjumper FSR Comp Carbon 6Fattie, Park City, UT.

Scott chose to pair a 2.8” tire with a 40mm wide rim on their Plus bikes. I didn’t notice any greater cushion from the 3” tires on the Stumpjumper, but the Schwalbe Nobby Nic tires on the Scott Geniuses exhibited markedly less casing flex. They felt more like normal bike tires, just bigger. The Specialized tires feel about like you expect them to: kinda balloon-y. Because the tire weights are similar I’d attribute it to the rim and tire widths.

Because the tires have a very rounded profile, they dive into turns quickly and bring your pedals close to the ground more frequently than you might be used to. Given this, the 175mm cranks start to feel pretty long. I hit them in a lot of places I didn’t expect to, so I’d swap them for 170 mm cranks.

On the Trail: Going Down

As soon as I finally got to point the bike downhill, I found the handling intuitive and lively. That was a bit of a surprise. The big tires look like they should monster truck over everything—and they do. But they can also dance around things better than you might guess. The shorter rear travel (130 mm vs. 150 mm in the front) helps to keep the bike responsive to trail inputs. That’s good, because the tires definitely numb trail feel a bit.

The big tires were really nice on loose surfaces. They let me steer by approximation through rubble and sand. Straights were great. Corners were different: there is lots of predictable grip on tap until the point in a corner when you would usually rail it. Instead, you drift. If you aren’t the sort of rider that loves to tip your tires on edge and rail turns, you won’t mind this trait at all. If you are that sort of rider, however, you might hate it. Might, but not definitely.

Other than on large hits, the suspension was great. Pedal-induced bob was minimal, and the suspension stayed active during braking. Through the mid-stroke, the suspension was supportive and supple at the same time. That made it all the more surprising when I would hit bottom. It happened a lot. And bottom-out was pretty hard. It became the biggest detriment to ripping rough downhills at speed.

Looking at the suspension curve, I could see why the Stumpjumper bottomed so frequently. The leverage rate increases toward the end of the stroke. I’d probably add volume spacers to the rear shock to try to get more ramp out of it. That said, many riders probably won’t find a problem with it.

NEXT: Tire Pressure, Issues, Etc.

5 comments on “2015 Specialized Stumpjumper FSR Comp Carbon 6Fattie”

  1. Sort of minor question…. the Specialized dropper lever is not compatible with a thomson? I’ve used one with mine for a year. Definitely a bit of a pull but works fine.

    • I know Thomson changed their setup at some point last year and flipped around how the cable is oriented. The post I have requires the swaged cable end to attach at the bottom of the post. The Specialized lever requires that the swaged end terminates at the lever. If you are determined, you could swage a second end onto the cable and make it work, but short of that it isn’t easily compatible.

  2. Great review. Love the depth. Every Specialized I’ve owned has been expensive — from pedal replacement costs due to their ridiculously low bottom brackets. No easy fix for taller guys, either.

    OTOH, it’s much easier to add a volume reducer to a Fox shock to reduce bottoming than it is to remove a non-existent one due to excessive ramp up. I like S’s approach in this regard.

    • Thanks Tom. I agree that it is easier to add a reducer than remove a non-existent one. I hope to add one to this bike to try it out. I’m not sure whether or not I’ll be able to get enough ramp though. It is very deficient and the shock already has a stroke reducer in it so I’m not sure how much I’ll be able to fit in there in terms of spacers.

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