Key points

• Dedicated 6Fattie rear end with Boost 148mm axle interface for improved tyre clearance and wheel strength
• Specialized uses a 150mm-travel Fox 34 Plus fork to correct the geometry of the 29er front end
• Tubeless-ready tyres and rims mean you can instantly drop 330g of rotational weight
• With 10 micro positions and a neat remote lever, Specialized’s 125mm travel IRcc Command Post is its best yet

As one of only a handful of Plus-size full-suspension bikes that are available right now, Specialized certainly can’t be accused of napping, as it did with the 650b standard. How has it managed to react so quickly to the latest development in wheel and tyre sizing? Only having to build a new rear end has certainly helped…

>>> Click here to find the best plus sized mountain bike

OK, that’s an over-simplification but the 6Fattie does share the M5 alloy front triangle with the Stumpjumper FSR 29, even if the 3in tyres and unique handling qualities mean the ride is a real departure from any ‘conventional’ Stumpy.

>>> Specialized mountain bikes: which model is right for you? 

Good fat: the Stumpy adds another level of grip in dry and dusty conditions (Kirkman)

It’s the only Stumpy at present to run 148 Boost dropouts and a corresponding rear hub. The stays flanking the 3in tyre mirror its proportions, and the back end feels every bit as stout as it looks. If you ride flat pedals, however, or have big feet, your shoes will brush the short, burly stays.

Suspension

Fox has really turned its 34 forks around; the latest generation is supple, supportive and, best of all, set-and-forget. The wide stance 34 Plus version, adorning the Stumpy Comp 6Fattie, sports 150mm of travel and increased offset to help keep the steering light and responsive.

The Stumpy generation game: old front triangle meets new fat rear end (Kirkman)

Out back, the Specialized Stumpjumper FSR Comp 6Fattie has 135mm of smooth, well-controlled travel, just like the regular 29er version. Set-up on the Fox shock couldn’t be easier, thanks to Specialized’s clever pump-and-release Autosag feature, and with three compression settings, you can instantly firm up the rear suspension for climbing, or open it up to blast the descents.

Components

Regular Roval rims, with a 29mm internal width, keep rotating weight down, but it’s debatable if they are actually wide enough to fully exploit the ability of the Plus size tyre to run lower pressures. We found that at pressures under 17psi (5psi more than the other bikes with wider rims), the 6Fattie tyres had a significant amount of casing roll when cornering hard.

Fattie uses spider-less single ring to modify chainline (Kirkman)

Also, the thin casing can bounce back aggressively on landings and g-outs at the slightly higher pressures demanded by the narrower Roval rim. In their favour, Specialized 3in tyres have a very rounded profile, that provides predictable cornering grip, even when the bike is really cranked over hard.

Performance

It’s easy to forget that there’s an extremely capable and well-suspended machine beneath you when you’re focusing so closely on tyre performance. Take a step back from the super-sized world of 3in rubber for a minute, however, and it’s clear that the suspension and handling of the Stumpy 6Fattie are everything you’d expect from a refined, modern trail bike.

Check out Specialized’s full 2016 Stumpjumper range

Sure-footed, capable and incredibly easy to ride, the 6Fattie is a real hoot. The sizing is spot-on too, and, thanks to the cushioning effect of the bulbous 3in tyres, you get the impression of having more suspension at your disposal than there actually is.

You don’t pay too much of a weight penalty, either, as it’s only fractionally heavier than the similarly-priced Stumpy Comp Evo 29 we tested last year.

Yes, the 3in tyres feel a little draggy at slower speeds, but since pedalling up the most technical climbs is easier, due to the massive amount of traction, over the course of a ride it’s about as fast as a bike with normal tyres.

Descending, the 6Fattie really builds up a head of steam, but there’s always a massive feeling of security to keep it in check. With more grip on tap, you can also brake later and get cocky with line choice without ever feeling like you’ll be penalised too harshly.

If it sounds too good to be true, it probably is. The catch here being that the wider tyres don’t like muddy, or boggy conditions. They can’t handle ruts and tend to float sketchily on top of mud and standing water. We also think the Stumpy really needs a wider rim to make the most of the fatter tyres.

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