All About 27.5 Wheels

Just got your head around 29ers? Well now, after a number of years on the fringe, we’ve got a third ‘in-the-middle’ wheel size to contend with—650B…

For the past 30 odd years, 26-inch wheels have been the accepted standard in mountain biking. More recently, 29-inch wheels have gained huge popularity; in some areas they’ve gained such momentum that they now outnumber their smaller counterpart.

With an outer tyre diameter of approximately 27.5-inches, 650B sits somewhere between the other two and it’s being touted as the next big thing—the wheel size that will bring about the death of the 26-inch MTB. So what’s it all about and where did 650B come from?

Coming Full Circle

While people have been riding bikes of all shapes and wheel sizes on the dirt for eons, the current MTB industry grew with a very strong influence from the USA. Back in the 70s Gary Fisher, Charlie Kelly and Tom Ritchey adapted 26-inch balloon tyre cruisers or ‘klunkers’ for their off-road adventures. Eventually they commercialised their hobby and the mountain bike evolved around 26-inch wheels. They clearly work too, as we’ve managed to do pretty well on them over the past 30 plus years. That said, there was no science behind their choice; it just happened that big fat balloon tyres were the most appropriate and accessible option for them at the time.

The funny thing is, it could have easily gone in a different direction. Way back in 1965 Geoff Apps was also modifying bikes for off-road use. As he was in the UK, he had a different range of tyre and rim sizes at his disposal. In 1975 he stumbled across the 54mm wide 650B Finnish made Nokian Hakkapeliitta snow tyres and built some of his own ‘Cleland’ brand bikes around these. He even shared this wheel size with his US counterparts but supply of the Nokian tyres was just too hard to come by.

The current generation 650B bikes evolved from a completely different source. It emerged largely due to the efforts of US-based frame builder/designer Kirk Pacenti. He became aware of the wheel size in 2004, and while he wasn’t actively searching for an alternative MTB wheel size, he immediately realised the potential that 650B held. As with the earlier UK-based adopters, the availability of tyres was the biggest hurdle. Pacenti pushed on to get Japanese tyre maker Panaracer to make a small run of real 650B MTB tyres—a big financial commitment on his behalf. That tyre was the 2.3-inch Pacenti Neo-Moto. Rim manufacture was an easier step, and Australian manufacturer Velocity rolled out some 650B hoops to suit. With availability of those critical parts sorted, bike designers were able to experiment with the size and it grew from there.

By 2009 brands such as Jamis, Haro and KHS had introduced 650B models and there were a number of smaller boutique builders playing with it too. Skip to the present and we have a large number of the fork, wheel and tyre manufacturers producing 650B product, with a good number of mainstream brands clambering onto the bandwagon.

Right Here, Right Now

In terms of ready-to-ride bikes that you may see on the shop floor, the actual numbers remain small, but the number of brands doing 650B has more than quadrupled compared to a year prior.

As some predict, 650B has already munched away at the number of 26-inch bikes offered by some brands. Scott for example has eliminated the 26-inch Genius from their range and now only offers it in 27.5 and 29-inch formats. Rocky Mountain has gone in deep with five 650B models on offer in Australia (the 150mm travel Altitude). Norco will be offering a 650B option on two frame platforms; the 140mm Sight and the 160mm travel Range, but only the Sight will be available Down Under for 2013 (it’ll be offered in two spec variants however). KTM will also bring three 125mm travel bikes to the table and Jamis will continue to offer both hardtails and duallies with 650B wheels. Even Aussie brand Craftworks will have a 130mm travel 650B trail bike on offer.

On the hardtail front, Focus will offer one model and smaller brands such as Carver, Van Nicholas and Lombardo will also have bikes to choose from. Based on the stats obtained from our Buyers’ Guide magazine, there should be around 30 individual models on sale in Australia for 2013. That’s barely a blip on the radar when compared to the 550 models with 26-inch wheels and 470 in the 29er division, but it’s still substantial growth compared to 2012. You’ll also find a large number of boutique brands who’ll have dedicated 650B framesets on offer (Intense, Ventana, Soma Fabrications and so on).

Size Matters

Where does the middle size fit into the game; how in-between is the ‘tweener? Let’s start by looking at the rim; 26-inch mountain bikes have a rim diameter of 559mm while a 29er is 622mm—an 11% increase. With a 584mm rim, 650B is 4.5% larger than a 26er.

From there tyres become the big variable as, in addition to varying in width, their height can differ markedly too. We measured a selection of tyres to get an idea of their true-to-life size once mounted and inflated.

Whilst you’d assume a 26-inch MTB had an outer diameter of 660mm (26-inches obviously), most were 672mm or bigger. Only the skinniest of 1.9-inch tyres came at their stated diameter. A popular XC tyre such as the 2.25 Schwalbe Racing Ralph was 673mm (26.5-inches) while a big-volume 2.4 Schwalbe Nobby Nic (a 700g trail tyre) was 683mm (26.9-inches). The 2.4 Continental Rubber Queen is another big one at 688mm (27.1-inches). A downhill tyre such as the Schwalbe Muddy Mary is 692mm or 27.25-inches, but it also weighs a ton!

An average 29er tyre such as the 2.25 Racing Ralph is 738mm; very close to the 29-inch mark and 9% bigger than a 26er wrapped in the same tyre. A large 29er tyre like the 2.35 Schwalbe Hans Dampf took the outer diameter to 749mm (29.5-inches).

As for the newbie size, with a 2.35 Schwalbe Nobby Nic the outer diameter came in at 700mm—that’s bang-on the oft stated 27.5-inch size. The original 736g Neo-Moto tyre came in at 702mm and overall the 650B tyres ranged from 698 to 708mm (27.4 to 27.9-inches). So our measurements indicated that your average 650B wheel is 3.6% bigger than a comparable 26er.

The commonly used naming (26, 27.5 and 29-inch) may lead you to believe that 650B sits halfway between the other sizes, but it’s actually a good deal closer to a 26-inch wheel. It stands an inch taller than a 26-inch wheel whereas a 29er is 2.5-inches taller—650B sits 40% of the way between the other two.

What Does it all Mean?

The current trend towards bigger wheels is driven by a number of performance traits. They typically have less rolling resistance, as the longer but narrower contact patch spreads leads to less sidewall deformation and energy loss when rolling. More importantly, the improved ‘angle of attack’ allows the bigger wheel to roll over obstacles with greater ease—it’s the old skateboard wheel versus bike wheel analogy. As a result, the bigger wheel provides a smoother ride with less bouncing around and this leads to enhanced traction in rough terrain. Lastly, by keeping the bottom bracket height the same and raising the axle height, you sit more ‘in the bike’ rather than perched on top. This combined with the greater gyroscopic effects of the larger wheels and typically longer wheelbase adds stability, giving the rider a confidence boost on the trail.

With a 29er, many of these benefits are quite noticeable—especially the roll-over advantage and stability. Of course the big wheels of a 29er don’t suit everyone or every application. It gets pretty tough to package more than 130mm of suspension travel into a 29er without the wheelbase getting kind of long and the front end tall for riders of average stature. Smaller people can have difficulty getting a good fit on a 29er—especially when you’re looking at a dually. Beyond the physical limitations that the size brings, many simply don’t like the feel of a 29er and still prefer the agility that smaller wheels bring on the trail. While XC-race oriented 29-inch tyres can be really light, they can get very heavy very fast once you add tough sidewalls and some decent air volume. Factor in the likelihood of additional wheel flex and it’s certainly understandable that 29ers aren’t for everyone.

That’s where 650B comes to the table. As it really isn’t much bigger than a 26-inch wheel, it’s easily packaged with lots of suspension travel. The long-travel trail bike market is where most 650B bikes are pitched for 2013. You can have 130-160mm of travel on a 650B bike without a ginormous wheelbase or chainstay length. In a different area, it will assist the XC racer who wants larger wheels but is too short to achieve the position they desire on a 29er. It’s also for riders who prefer the more agile handling of a 26er but want to run wheels that are bigger than 26 inches.

Another point that has already influenced the uptake of 650B is that the comparatively small 12mm radius increase allows it to fit in some existing 26-inch bikes. You just need to ensure the tyre doesn’t hit anything when the suspension is bottomed out and in some cases travel reduction spacers may be needed to prevent tyre-to-frame contact. If you’ve got plenty of tyre clearance on your existing 26er and the bottom bracket is on the low side, you may well have an ideal conversion candidate—there’s plenty of information on the MTBR forum about people’s ad-hoc 650B conversions (http://forums.mtbr.com).

Taking the B-line

For all of its ‘ease of packaging’ benefits and the ability to combine it with long travel suspension, you’ve also got to ask if the three-to-four per cent size increase is enough to gain any worthwhile benefit. The statistics suggest it’s not going to produce a dramatic change but as with many things, you never know until you try it for yourself.

We’ve gained our experience from retro-fitting 650B wheels to our existing bikes (we did this as far back as 2008), as well as test riding some of the new generation 650B models. Having ridden and owned countless 29ers, we know how they feel—the differences are clear, both for better and for worse.

The in-betweener on the other hand feels a lot like a 26-inch bike. As you’d expect, the 3.6% size increase doesn’t stifle manoeuvrability and you can throw a 650B bike around just like a 26er. With their equal to 26er geometry, they are flickable and capable when airborne and they don’t feel sluggish or stifled in twisty singletrack. Bikes with 650B wheels are likely to possess a fun and engaging ride for a technically adept rider—just like a good bike with 26-inch wheels.

On the flipside, they don’t have a distinct roll-over advantage and they aren’t that different to 26-inch wheels in relation to their smoothness on the trail. When mounted to a hardtail the difference is more apparent but factor in 130 or 160mm of travel and things can get pretty well blurred. With bikes in the 150mm travel category, such a small difference in wheel radius tends to be overshadowed by the suspension performance as a whole—especially once you are up to speed. In other words, adding 650B wheels to a sub-standard suspension bike won’t have you blitzing the descents like you would on a well-sorted 26-inch dually.

At lower speeds and in stepped terrain there is a small improvement in roll-over-ability, but it’s far less obvious than the advantage offered by a 29er. The 650B feel is somewhat like running a big volume tyre on a 26er, but without the same amount of added tyre weight. When it came to straight-out rolling resistance on smooth terrain, the difference wasn’t great enough for us to detect.

We’ve heard plenty of people spruiking the performance benefits as being huge and clearly noticeable, while also having none of the compromises that 29ers bring. Although 650B successfully sidesteps the big-wheel drawbacks, it also didn’t have us noticing huge advantages over the smaller wheels. Riding 650B wasn’t a cathartic or spiritual experience for us, it was however a lot of fun. The wheel size definitely works well on the trail and caters for a broad range of applications without compromising suspension travel or fit.

In recent times the public image of 26-inch wheels has copped a flogging at the hands of various 29er marketing campaigns. With the advent of 650B you can gain a slice of big-wheel pie without incurring major drawbacks. Of course the benefits are nowhere near as pronounced but there are no magic bullets in this world. If you’re in the market for a new trail or all-mountain bike and prefer a playful feel, a good 650B machine could be a terrific choice, but we don’t feel you need to rush out and offload a perfectly good 26er to hop onto the 650B revolution.

At this point mountain bikes perform brilliantly and you’re not going to encounter huge evolutionary leaps. Improvements come about with incremental change. Given the undeniable popularity of bigger wheels, and their inherent limitations, 650B may well be the incremental step that many mountain bikers have been waiting for.

Kirk Pacenti summed it up pretty well when we spoke to him, “For me the real strength is that the wheel size works well on all frame types and sizes. Whether it’s fully rigid single speeds or a six-inch travel dually—a company can create a range of well-designed and well balanced machines in every frame size, all around one wheel.

I also think the performance of these bikes will speak for themselves—this is what is going to push the 650B wheel forward. I don’t have any delusion that 650B wheels will replace the existing wheel sizes, but I do think it can become the preferred standard among bike makers and bike riders alike.”