The 35-year-old Specialized Stumpjumper has been on the market for more years than our average reader has been alive for (FYI: 33 years). Since this Californian classic first emerged, it has been through many iterations over the years, and Specialized now produce a hardtail range of the Stumpjumper as well as full-suspension models in all three wheel sizes. We’ve compared the Specialized Stumpjumper FSR Expert 650b against the 6Fattie to find out which bike is for which type or rider.

Specialized Stumpjumper FSR Expert
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Right from the get-go, Specialized have been one of the loudest advocates of bigger wheels, and were the first brand to design a complete 29er line. They’re doing the same with plus bikes: at this year’s 2015 Sea Otter Festival, the Californians launched their first model, with other models following over the course of the season. One of these was the Stumpjumper Expert Carbon 6Fattie, which we’re comparing to its 650b counterpart. As the US bike giant also produce their own tyres and wheels, the origin of these was never going to be up for question. The Stumpy 6Fattie takes 3.0”-wide tyres and matching wheels with a 29 mm inner rim diameter.

The first impression of the Specialized Stumpjumper FSR Expert

The same name, the same price, a virtually identical spec, but glaringly different geometry – these are the basics in this comparison. Of course, the chubby tyres need some extra space, so it’s not surprising that the rear end on the 6Fattie plus bike is a few millimetres longer. (In comparison to the 650b model, the 6Fattie (like the Stumpjumper 29er) measures in at 17 mm longer.) But if they’d only extended the rear end, then the bike would have turned into a lumbering beast with a vice-like grip. In order to address this, Specialized also designed a more compact frame for their bikes with bigger wheels. On the 6Fattie you’re fairly upright as you ride, while the 650b model puts you in a more aggressive position – due to the longer frame and 80 mm stem, you’re pretty stretched out over the bike. Both bikes came under fire from our test crew for their Specialized Command Post dropper post, as its rearward offset wasn’t well received and proved a limiting factor on super-steep ascents. This is a crying shame, as the Command Post’s ergonomic lever is damn good!

Specialized Stumpjumper FSR Expert 6Fattie
The Specialized Stumpjumper FSR Expert 6Fattie comes with a 150 mm Fox 34.
Specialized Stumpjumper FSR Expert 650b
The Specialized Stumpjumper FSR Expert 650b in contrast boasts a 150 mm RockShox Pike.

So while both are comfy to ride, and there’s nothing holding them back on climbs, where else are the differences? The biggest benefit to the 650b model has to be its incredible acceleration, while the 6Fattie just blows it out the water with its traction (despite the fact that the tyres have a super-low-profiled knob design). Specialized have mounted the 3” tyres on 29 mm-wide rims, giving the tyres a satisfyingly round form. Without any pressure on them the side knobs are really deep, but they creep around the top once you’re on the bike, which creates a really great sensation when you’re riding that’s similar to the 27.5” model. However, that typical tendency of fatter tyres to deform on berms and compressions unfortunately hasn’t been eliminated.


When it comes to handling, both the Plus and the 650b Specialized are unlike any other bike in this test. The 6Fattie is agile and playful without any twitchiness. The 650b model, on the other hand, is smooth and capable without any hint of lumbering. Given the long frame, the 27.5“ demands a more dynamic rider, as you need to keep it under control with pressure on the front around corners. This makes it more suitable for skilled riders with a knack for slight repositioning depending on the terrain. Inexperienced or less aggressive riders will benefit from the 6Fattie’s more compact geometry, which gives it a super-balanced feel and allows it to be willingly steered down your chosen lines. Its linear rear end is very generous with the travel – perhaps overly generous at times – but this does deliver a huge amount of comfort.

Specialize Stumpjumper FSR Expert 6Fattie action shot Specialized Stumpjumper FSR Expert 650b action shot

The Bikes in Detail

SWAT door on the Specialized Stumpjumper FSR Expert 650b
SWAT Box: Get lost, backpack! Thanks to the SWAT box on the frame, any tools you need can be stowed in here.
Rims and tires of the Specialized Stumpjumper FSR Expert 6Fattie
Rim width: Is wider really better? The 29 mm inner diameter is more than sufficient on these Specialized rims, giving no rise for complaint.
 RockShox Pike Federgabel im Specialized Stumpjumper FST Expert 650b
Forks: Both the FOX 34 and the RockShox Pike work brilliantly on these two bikes.
Frame of the Specialized Stumpjumper FSR Expert 650b
Geometry: The Plus bike’s rear end design is slightly longer, the frame shorter, and the handling more balanced.

Which bike is for who?

Specialized Stumpjumper FSR Expert 6Fattie

Ideal for both dynamic trail riders who’ll gently tap the brakes late and love to ride on natural trails, as well as newbies who are after a touch more stability on the ride.

Specialized Stumpjumper FSR Expert 6Fattie action tested on the trails

Specialized Stumpjumper FSR Expert 650b

A bike designed for maximum fun on your local trails. But don’t limit its fun; take it to the mountains or the bike park, as this bike can literally do anything.

Specialized Stumpjumper FSR Expert 650b testd on the trails


Specialized realised that they needed more than just different wheel sizes to create a solid, trail-worthy packages for their buyers. With these concepts cleverly designed for every sort of rider, the bikes just work. Experienced riders should grab the 650b model, while less aggressive riders will surely enjoy the stability that comes with the Plus model.

For more information visit the Specialized Website


This article is part of our group test: The Duel of the Tyre Sizes: 27.5+ vs. 27.5″ and 29er Bikes

Don’t miss the other bikes from the test:
SCOTT Genius 900 Tuned vs. Genius 700 Tuned Plus in Comparison
STEVENS Whaka ES 27.5” vs. 29” vs. 27.5+ in Comparison

Upadate May 2016: We’ve also had the Specialized Stumpjumper FSR Expert 650b in our trail bike group test

Words & Photos: Christoph Bayer

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