6 F Attitude - Stumpjumper 6Fattie Review - Dirt

Mountain Biking Magazine


Trail and Enduro Bikes

6 F Attitude – Stumpjumper 6Fattie Review

Apprehension of my first encounter with 650+ was transformed to excitement within a couple of turns, twenty foot of limestone, and a delta of douglas root. Anticipating the worse on a wild entry into a flat left I was embraced with grip, pulled into a cuddle and thrown a saddle bag of grip before trotting off into the sunset. Elated on a deflated tyre. Whatever next.

Visit any mountainbike suspension company and they’ll more than likely have a four wheel drive vehicle to get to work and events, maybe relying on the cushioning a good deep tyre gives to the ride. Maybe its because they like a bit of travel in their ride, or maybe that in simple terms if they’re running bigger tyres they prefer the softer spring rate that the big rubber provides.

But as much as big tyres are part of everyday off road truck and tractor life, finding the balance between grip and comfort is a massive part of mountainbiking. After all a bicycle needs as much help as it can off road. Changing the tyre size affects the spring rate of the bike, this in itself is huge before you begin talking tread patterns and pressures. In general lower profile tyres effectively give better lateral performance but the vertical spring rate changes and the cushioning from the trail goes down.

No surprise then that big tyres are back on the agenda. Common sense would tell you that they’ll offer a more comfortable ride through brutal grounds, but how far are we from getting a tyre tuned to the bike? We take a ride on the new Specialized 6Fattie.

By S.Jones

Action: Ieuan Williams

Photos: Ben Winder

It’s a much asked question. “What do you think of 650 plus – the larger volume three inch tyres?” Initially not so much really, Michelin 2.8’s and 3.0” Nokia Gazzaloddi were part of the downhill scene almost twenty years ago, we were in no rush. That’s not true, we were intrigued, but we waited until winter to see whether a tyre with an outer diameter only slightly smaller than a 29” and width not massively different to a 2.4” tyre offers better performance.

It all comes down to familiarity. It takes a while to adapt to the ways and looks of a bike with a wider fork and fatter tyre – not fat enough to make it daft, just make it different. 6Fattie gives the bike an association with the huge rubber hardtails but don’t go comparing this bike to such beasts. The 6Fattie could probably do without the association with those bikes for it simply has a slightly wider tyre, fork and swingarm. What we have here is a 135mm travel Stumpjumper with 3.0” tyres rather than the 2.3” featured on the standard 650B model.

Up front - 3.0" Specialized Purgatory
Rear - Specialized Ground Control via the ever- impressive FSR suspension

SHAPE AND PURPOSE – In many ways the 6Fattie is very like its other Stumpjumper stablemates – the 650B version and 29” bike. At 135mm rear, 150mm front, its in and around the same travel as the 650B Stumpy (150/150mm)  and the 29” version (135/140mm). Very much a trail bike through and through, both its brothers are very pacey bikes.

“Want to improve the smoothness of your ride but cannot really afford the hefty damper price tags? Then consider getting a 3.0” tyre”

When you look at the dimensions there are some key differences. The 6Fattie has a longer reach, lower bottom bracket, different fork offset (51mm offset compared to 42mm on 650B), longer wheelbase and a hugely different chainstay length – 437mm compared to 420mm on the 650B Stumpy. The 6Fattie is fitted with 3.0” Purgatory up front (980g) and Ground Control rear (1045g). Both are slightly heavier than their 2.35 brothers by almost 200g.

In terms of detail, superb Shimano XT brakes, perfection and reliability in the new Command seatpost, unflinching shifting in Sram X01 and yet a bloody awful pair of hubs that packed in after only a few weeks.

RIDE – Apprehension of my first encounter with 650+ was transformed to excitement within a couple of turns, twenty foot of limestone, and a delta of douglas root. Anticipating the worst on a wild entry into a flat left I was embraced with grip, pulled into a cuddle and thrown a saddle bag of grip before trotting off into the sunset. Elated on a deflated tyre. Whatever next.

Well, the tyres continued to give, roots and rocks pushing into the carcass of the thin Purgatory rubber, conforming to ground debris, isolating the chassis and rider from the same type of vibration encountered on standard tyre sizes and pressures. As a giver of confidence this was generous stuff. Off cambers, root riddled conifer woods, flat clay skate sections, it continued to amaze – improved traction? Yes.

Day two of increased adhesion dawned gloriously wet and miserable. But before that some surfaced table tops, washed out sandstone beads, harder grounds where the heightened roll over performance and ability to straightline rock sections became a clear advantage but so too the bounce, the slightly hard to control space hopper effect on take off, landing and many of the bits in between.

This slight disconnect between rider and ground compared to a normal tyre running higher pressures and linked to good damping and wheel flex/stiffness is a difficult one at first but you get tuned in pretty quickly. But its important to remember low pressure on similar weight 2.35 tyres has the same effect on the ride dynamic. Its early days and control will only improve with different sidewall support and design but for now one of the basics of advanced riding – weighting and preload in both tyre and suspension is slightly more difficult with low pressure tyres and weak sidewalls that collapse momentarily when loaded.

Overall the grip was impressive, the body takes less of a beating in harsh rocky tracks and line choice becomes less of an issue – straight through the lot. The cushioning effect of the big tyres means that arms and legs remain relatively fresh compared to harder sidewalled narrower tyres running higher pressures . On unseen enduro stages the tyres could offer advantages if the puncture count remains low, we’ve managed several day trips to Bike Park Wales without any flats. This together with the fact that rolling resistance was low and the excellent geometry will have many people taking a serious look at this bike.

Sram - simply never misses a beat, and easily the best in mud
Sram chainset is down to 28T offering super low gearing
Specialized Command seatpost is gradually becoming our favourite for reliability
Shimano XT brakes. Good, but not quite Sram Guide's

DETAILS – Rims. Tyre combinations and avoiding generalisations.

In many ways it has taken a while to get used to the ways of the bigger tyre similar to the period of adjustment it took to get used to 29” wheel bikes. Different timing has been a key here too. The less than aggressive pattern of the Purgatory/Ground Control tyres combined with the 29mm rims gives a very round profile with relatively little edge. It’s a combination that leads to pretty normal cornering characteristics and certainly quite different to the 40mm wide rim/Nobby Nic tyre combination we’d ridden on the Scott Genius Plus bike.

“in muddy conditions the tyre sheds more dirt than standard 2.35 tyres partly due to the increased flexing because of low pressures”

So we mounted the Stumpy with the more aggressive but slightly narrower 2.8” Schwalbe Nobby Nic tyres in Pace Star compound and (obviously) found quite a different ride characteristic, offering more bite in cambers. That said, the compound felt better on the Specialized rubber. We also found the bike stood up a touch in the corners with the Schwalbe’s fitted, not quite as much as with the 40mm rims, and something we didn’t encounter on the Specialized rubber. This could be rider error – braking when there’s no need to and also the fact that in muddy conditions the tyre sheds more dirt than standard 2.35 tyres partly due to the increased flexing because of low pressures. The tyre clears well and regularly has more bite on offer.

In terms of rims the bike features 29mm wide Roval Traverse rims taking a markedly different route to other bike companies who run upto 40mm rims on the wider tyres. In short we’re not convinced that wide rims actually help at all, happy with the standard 29mm rims although found a nice balance at 35mm too.


We swapped out the daft bar and stem for a Burgtec RW carbon and 35mm Easton
Specialized cable routing - slowly getting tidier
Rear - Specialized Ground Control via the ever- impressive FSR suspension

Rolling speed. There is an idea that the big tyres are sluggish and don’t roll very quickly. This is a myth as we found on longer day rides where climbing is definitely easier.

As for timed testing the bike seems to yield different times in different conditions. Having ridden and timed the Stumpjumper against a variety of bikes, in different locations and surfaces we simply cannot draw any reliable conclusions yet. The tyres work better in some soil conditions than others. In fact every track hit us with different results. On muddy flat, rooty tracks the 6 Fattie even with the low profile Purgatory/Ground Control rubber was close in times to 29” with mud tyres and faster than standard 27.5” with normal dry rubber. Then on long rocky descents as found in Bike Park Wales the times compared with standard dry rubber was too close to call even though we were getting more tired on the standard rubber.

Yet even though the timing has proven inconclusive, and track specific, and the poor compound is not ideal, we found more poor compound is better than less poor compound. In other words a 2.8” Pace Star Nobby Nic had considerably more grip than a 2.35” Pace Star Nobby Nic. And the super low profile Specialized Purgatory/Ground Control 3.0” tyres offer more grip at lower pressures than a normal tyre with higher pressures. There’s a lot to take in.


Comparisons will be made. Whilst the 6Fattie offers more grip, more stability, more cushioning than its 650B Stumpy stable mate its very much dependant on the terrain. In pure mud riding a 29” Stumpy with mud tyres will offer better, faster performance but in a pile of root and rock there’s no disputing the benefits of the 6Fattie. And remember you could fit 29” wheels into this bike without much of a change in geometry.

There’s definitely something in this, for the novice rider it will instil huge confidence, whilst the lack of connection to the ground so central to higher level riding will put some riders off. Having said that, the ability to charge through rock and root at higher speeds without the same degree of chassis feedback as a smaller tyre many will find liberating. It has certainly made us a smile every time.

650 + is for beginners did I hear someone say?

Is it sluggish? No. Do they puncture? We didn’t have many flats however you do need to be very careful with pressures as the window of balance/grip for rider weight is quite small. At 90kg we had to get the pressure to 20psi. You do also need to tune your timing slightly. The bottom line is that if I was in the market for a Stumpjumper this is the bike I’d choose. And if you’re unsure then simply fit a pair to your current bike to try as they seem to fit a lot of bikes.

But ultimately this all pretty basic stuff, we look forward to experimenting with different tyre/damper settings and eagerly wait for a bigger spread of tyre sizes, stiffer sidewalls and compounds. Its all only just beginning, and how long before we see the really good brands getting tyres tuned for each bike in the range?


Price: £4800




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