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27.5+ vs 29+ tire mountain bike tires

Trek suspension engineer, Ted Alsop, puts it this way, "27.5+, ideally, has the diameter of a 29×2.3 tire, but to get there, you have to give it a really tall sidewall. The bead-to-bead measurement-that's the actual width of the tire if you pressed it flat and measured from one bead to the other-is about 15 millimeters wider than a 29+ tire. Relative to the rim, the 27.5+ tire is actually taller than the 29+ tire, which is why we've found that the 27.5+ tires that we've ridden have a lot more of an un-damped, fatbike tire bounce to them and don't corner as well at lower pressures. The 29+ tire, which is actually a lower profile, shorter sidewall tire, has less of that uncontrolled bounce to it."

What are plus-size bikes supposed to offer? At this point, it all depends on whom you ask. For Alex Cogger, director of product for Rocky Mountain Bicycles, plus-size bikes, like the new 27.5+ Sherpa, have a very definite, limited skill set. "What they do really well," says Cogger, "is monster truck over stuff. They really shine in loose, rubbly, crappy conditions. It's great for that. It's also incredibly stable and grippy, so for someone who's less technically skilled and is looking for some added confidence, absolutely."

"Where it begins to falls short," adds Cogger, "is for someone who is trying to push really hard in the corners and get really aggressive-that's when you get some tire roll. You'd have to make such a burly and heavy tire for it to not fold over like that, that you'd just be bolting extra weight onto your bike."

Accordingly, Rocky Mountain has positioned the Sherpa as an overland adventure bike.

Other companies, however, have a decidedly different take. The most obvious of which is Trek Bicycles. A few days ago, Trek unveiled its new Stache plus-size hardtail. The bike wears 29+ tires and has an entirely different mission statement than the Sherpa.


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