It reads like the back emblem of a BMW; full of numbers and letters that to some may clearly denote where their particular car fits into the spectrum of models available or more likely, how it bests their buddies over priced car. Well 27.5 or 650B as it’s known by the in vogue techno bike geeks isn’t a bike model but rather a wheel size.
For countless years mountain bikes rode on 26″ wheels with no differentiation between bikes of various disciplines. While all other things changed over time from frame construction materials to brake systems and numbers of gears wheel size remained for the most part static. The 29er (29″ wheel) movement built momentum over many years and by it’s undeniable virtues rose in popularity. Fast like a freight train? check. Levels rough terrain with ease? Check. Gobs of traction on climbs? Check that too. Well it wasn’t all good. It became clear that 29ers had their place and that place was in the realm of hardtails and shorter travel xc bikes. Applied to longer travel bikes, the 29er template became a little less manageable for bike engineers and a little less fun for riders. This is not to say there aren’t some fantastic 29er trail bikes out there because there surely are but riders want bikes that corner on rails, turn with only the slightest body input and accelerate like a cougar who just spotted his lunch…and some riders want all of that with heaps of travel too. Let’s not even get into how hard it is to fit short riders on wagon-wheeled bikes!
Riders want it all and they want it with all the glorious benefits of the 29er but with none of the drawbacks. Shocker, we all want bikes that are fast, nimble, light and make you feel like your a world cup pro every time to tear down a trail. Like many companies, Giant saw not only the benefits but the limitations of 29ers and decided to do their homework. How do 26, 29 and 27.5 wheels actually function under rigorous, controlled testing? It’s one thing to get the opinion of the many wheel size aficionados or even to test ride a few different bikes but you can’t argue with the hard facts…
27.5 as it turns out offers a great deal of the benefits of both 26 and 29″ wheel sizes. They don’t fit neatly in the middle however; that’s an over simplification of the facts. They’re lighter than 29er wheels (6% on average) and therefore more responsive (aka faster acceleration or ‘snap’, more like a 26er), they provide great terrain levelling capabilities (improved angle of attack); not quite as much so as the freight train 29er wheel but far more so than the ol’ 26er standard. Traction is significantly improved over a 26er while giving up little to a 29er. Larger wheels offer a larger contact patch with the trail resulting in more traction while climbing, leaning into turns or roasting through a rock garden. A 27.5″ wheel’s contact patch is nearly identical to that of 29er; only one centimeter less.
The true superiority of the 27.5 wheel size lies in it’s ability to be applied to a variety of bike types. Cross country, trail, enduro and even DH and freeride mountain bikes can be engineered to work with 27.5 without giving up critical elements in the process. Frame geometry can be optimized for the ride not just to make the wheel size work therefore key dimensions that improve ride characteristics are not compromised. Shorter chain stays and overall wheel base (for a faster turning, responsive or ‘poppy’ bike), lower front end heights (for a comfortable, efficient riding position), reduced frame and wheel flex or deflection (for a more confidence inspiring ‘on rails’ feeling ride).
Will 27.5 become the new norm? It’s certainly possible. Will 29ers go the way of the dodo bird? Not likely…after all they’re fantastically fun in the right application but you can bet that 27.5 is here to stay and once you try one you’ll know why.