When Specialized debuted the new Stumpjumper a few months ago in New Zealand, they announced 27.5+ versions of the bike and its women’s counterpart, the , but had no working 6Fatties—the name the company has given to their plus-size wheels. Earlier this week, however, while I was on other business in Northern California, the company offered me a chance to try out the first rideable Stumpjumper 6Fattie.
We hit up a morning ride at , halfway between Morgan Hill and San Jose, for a few laps before my midday flight home. It’s not the region’s most compelling mountain bike destination, but the trails are rough and littered with jangly rocks, a perfect testing ground for semi-fat tires. Specialized engineers used the area heavily, especially the two-minute Stiles Downhill, as they developed 6Fattie bikes.
, Specialized’s Global PR Manager for mountain biking, picked me up early, with an and in the back of his truck. Even though I logged multiple big rides on the 29er in New Zealand, the idea was to compare the two back-to-back. At the trailhead, we were surprised to find , who showed up with a Fuse in tow in case there was time for me to try it, too.
First up: The Stumpjumper 6Fattie, which pairs the line’s trail-oriented geometry and all-around characteristics with three-inch wide tires mounted on 27.5-inch wheels. The fatter tires mean the wheels measure to about the same as a 29er, but they allow for lower tire pressures and the resulting traction benefits. I was surprised that the bike will be spec’d with the same 30mm-wide equipped on the standard Stumjumper FSRs, but Cannatelli said that testing showed the advantages of the lighter weight outweighed the small performance increases of wider rims.
Given the extra weight in rubber, the Stumpjumper 6Fattie isn't for everyone. But it’s as fun and easy-to-ride as a bike can be on loose, rocky terrain. Given my extensive experience on the Salsa Bucksaw, that came as no surprise.
On the trail, the Stumpjumer, with the 150mm up front, 135mm of rear travel, and a middle-of-the-road 67.5-degree head angle, proved as forgiving as it looks. On the Stile’s jumble of nasty fins, steps, and fangs of rock, the wide tires and full squish made line selection almost a non-issue. The 27.5+ size makes descending almost as easy, though the carbon rims and lightweight parts on the bike make it feel far more maneuverable than the tires suggest. Given the extra weight in rubber, this won’t be a bike for everyone. But it’s as fun and easy-to-ride as a bike can be on loose, rocky terrain. Given my extensive experience on the , that came as no surprise.
The Fuse made an even bigger impression. Sean sliced a sidewall on the Stumpjumper 29er on the savage first descent, so rather than risk a blowout on that bike, I opted for the hardtail 6Fattie on lap two. , and the women’s , is an alloy hardtail with plus-size wheels released at . It’s analogous to Trek’s new Stache, but instead of 29+, it mates 27.5-inch rims and three-inch tires to a slightly shorter rear end and even slacker head angle (67 degrees) than is on the Stumjumper. The bike will come in three builds: Pro ($3,100), Expert ($2,100), and Comp ($1,600).
Cannatelli’s Fuse Pro featured a custom build, with upgrades including 38mm-wide carbon rims (the Pro comes with alloy) and a 120mm Rockshox RS-1 fork (instead of a Reba). It also had Specialized’s new Purgatory 6Fattie tire, which is meatier and has more side knobs than the Ground Control I’d ridden on the Stumpjumper. The result was a machine that leapt up the steep, chunky climbs with the vigor of an XC machine, but tracked through the chunder of the descent with much more ease than any standard hardtail I’ve ever tried.
Both bikes were excellent for the rugged trails, but the Fuse in particular left me thinking that 6Fatties—and plus-size bikes in general—are here to stay. The big tires will likely be too heavy for World Cup racers, but otherwise I can’t imagine a future hardtails without these wider tires. The near-29-inch diameter smoothes the rough trails and compensates for the lack of rear suspension, and the fat tires make line choices easier and the ride more comfortable than on a standard hardtail. For me, the jury is still out on whether the optimal setup is 27.5+ or 29+—a question I’m working through at the moment with the new Stache—but I rode away from Santa Teresa believing that plus-size wheels are the only way forward for hardtail mountain bikes.
Cannatelli underscored that sense after our second lap. Just back two days earlier from Spain’s upcoming Enduro World Series stop, , which is renowned for its burly, rough trails, Cannatelli said he had no trouble keeping up with bigger bikes on his Fuse. “Everyone told me those trails were too much for a hardtail,” he said. “But the 6Fattie isn’t a typical hardtail. When people start riding these wider tires, they are not going to want to go back. I never will.”
We’ve devoted extensive coverage to fatter-tired bikes lately, and that’s not only because they're new news. From my experience, plus-size (and fat) tires legitimately change the ride experience more than any single development in the past couple of years. How the technology will develop remains to be seen. But there’s no question in my mind that, one way or another, mountain bike design will gravitate toward fatter, more forgiving tires in coming years. Just ask Sean, who, after slicing his 2.3-inch 29er tire, was wishing he’d been riding thicker rubber. As more people try plus-size tires, I anticipate many will have the same reaction.