A freak thunderstorm, nearly tropical in magnitude, spent 10 minutes stripping the loose soil off the steep trail near my home in Southern California. The water carved a six-inch-wide rut; then the sun baked what dirt remained until it was rock-hard with only loose pebbles left on top.
I attempted the section a few days later on one of my favorite, 160mm-travel enduro bikes—and just barely made it through without crashing. The next day, I took out the Specialized S-Works Stumpjumper FSR 6Fattie, and rode the entire thing, dabbing only once. This moment convinced me that the 27.5+ tire trend is not just a fad—these 2.8-to 3.25-inch-wide tires provide a legitimate benefit.
The 2016 Stumpjumper comes in three options: 29-inch, 27.5-inch, and 6Fattie, Specialized's new 3-inch-wide, 27.5-inch-diameter trail tire. The 6Fattie Stumpy has a lot in common with its 29er brother, including the same 135mm-travel FSR rear-suspension design, and a rear end that was beefed up for 2016. Its chainstays and 150mm-travel Fox fork are spaced wider to accommodate the fatter tires. On the carbon models like the S-Works version we tested, a SWAT (Storage, Water, Air, Tools) compartment houses a tube, pump, and whatever else you can fit inside the down tube. I avoid wearing a hydration pack whenever I can—I find them to be hot and uncomfortable—and I love how the SWAT gets the weight off your back and stashes it low on the bike, where weight is less noticeable. According to Specialized, engineers were able to harness a 69 percent larger (compared with a 2.3-inch tire) contact patch during their test rides thanks to the extra width and ability to run lower tire pressures. Compared with the 20-or-so psi I typically run, I found that I could drop to 15 psi in the 6Fattie. All this extra footprint gave the tires a tenacious grip on steep and normally slippery surfaces, even when I was out of the saddle. A 28-tooth chainring on the 1x drivetrain typically would be on the low side for me, but it was well matched to the plus-size tires' climbing prowess and the grades they allowed me to scale. I rode more and walked less on the 6Fattie—and that's a win for any mountain biker.
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Rim width is critical with wider tires, as the tire can fold over and wallow without sufficient tire pressure. We've had the best experience fitting plus-size tires on 38mm rims and up, but Specialized went for light weight here and chose its 30mm-wide Roval Fattie carbon wheels. The company says that the suspension on the Stumpy allows the rider to run slightly higher tire pressures than on hardtails (which most of the new plus-size tire models have been) and thus have less of a need for a wider rim. And it makes up for the weight penalty of the wider tire. I think it was a good call, as acceleration and handling felt surprisingly similar to a traditional 29er.
I tend to be skeptical about new standards unless they significantly enhance the riding experience—but I think plus-size tires and SWAT accomplish this. Like any new technology, plus-tire wheels and frames will improve over time. But with this early stab at 27.5+, Specialized created an impressively dialed and cohesive-feeling unit, not a half-baked idea.
Confused about which wheel or tire size to commit to? Specialized says that its 6Fattie is for riders who want more traction and control, 27.5 is for those who want more nimble handling, and 29ers are for those who value speed. I think they nailed it. Plus-size tires probably won't ever be popular on cross-country racecourses, but for those of us who ride outside the tape, bikes like the 6Fattie Stumpy offer a genuine performance advantage—and the ability to have even more fun.
What You Need to Know
• 3-inch-wide tires offer more traction than traditional-width tires
• Also available in a women's version, the Rhyme 6Fattie
• Prices at $3,400 for Comp Alloy build
Price: $8,600
Weight: 27.6 lb. (M)
