First contact: the 27.5 inch mountain-bike

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The latest KTM presentation of their 2013 bike range was the perfect occasion to pedal a few laps on a bike equipped with the new 27.5 inch (or 650B) wheels. As there have been a lot of discussions regarding this news size, curiosity was at its peak, so the 130 mm full suspension aluminum frame KTM Lycan was our perfect candidate.

So, what’s with this new wheel size?

In brief, 27 inch wheels were launched as the field’s new revelation, as they should represent the best compromise, not too small (26 inch), not to big (29 inch). And the golden mean has always been the most balanced solution, as this is the manufacturer’s argument right now. Of course, discussions might be endless, so have to skip to the hard facts.

In order to better understand the advantages of 27.5 inch wheels, the table below shows the obstacles passing ability of a wheel, according to its size. The angle made by a 29 inch wheel and an obstacle is the smallest, while for a 26 inch wheel, the angle is the highest. Of course, as the size of the obstacle grows, so does the difference between the 26 inch wheel and the 29 inch wheel.

27.5 inch wheel. Obstacle passing

The weight differences between the wheels are shown in the table below and they are hardly surprising, as a 26 inch wheel uses smaller components, while a 29 inch wheel uses a bigger rim, longer spokes and a larger tire. And more material could only mean more weight.

27.5 inch wheel – Weight (hub, spokes, rim, tube, tire, quick release)

The gyroscopic momentum is the force dictating wheel behavior. You can make a very simple experiment, by tying a rope to the hub. Hold the rope, put the wheel into move and observe its behavior (higher stability for a larger diameter and vice-versa). Using the rope, you will be able to turn the wheel right or left, and observe how difficult or how easy it changes direction.

This experiment helps us get a clear picture about how maneuverable is that particular bike. As you can notice, the difference between the 26 inch and 27.5 inch wheels is not big and this can be felt right away on the trail.

How does the 27.5 inch bike rides?

I would be tempted to say that close to a 26 inch, but with small doubts regarding acceleration which seemed a bit poorer. Handling is fine and I haven’t noticed any notable difference, even if I also pedaled on 26 inch bike on the same track.

Obstacles passing capacities are better on the 27.5 but not better as it is the case for a 29 er. Keeping up speed is easier with the 27.5, but when it comes to very difficult tracks, with tight corners, where you have to brake and steer the bike with your body, I prefer the 26er.

Hence, my conclusion when it comes to the utility of this wheel: it is a perfect tool for Cross Country, Marathon or All Mountain races, but when it comes to difficult disciplines like Freeride, Downhill or Dirtjump I almost have no doubts that this size won’t have to much chance. But I might be wrong, as after all we will all see what happens in the near future.

Are there any disadvantages?

Well, right now they exist, if we take a look at the higher costs of components. Manufacturers seem to profit from this status quo, as the forks and wheels are more expensive than the same parts for 26 inch wheels. Same as for 29ers, prices will have to go down in time, but until then you will have to spend some extra cash if you want to ride a 27.5 inch mountain bike.

27.5 inch bikes have frames built on purpose for this format, but KTM says that there are some 26 inch frames which fit with the new wheels. Yet, we have to think at the frames angles and the clearance, it would be rather difficult to mount a 27.5 inch wheel on a fork designed for a 26 inch wheel.

If you are ready to accept a few hundreds grams more, then weight will not stand a decisive in buying such bike.

Right now, producers offer a very narrow range of components, but for sure you will be able to find a tire, a rim or a fork, in case you’ll need one.

Conclusions

It’s hard to spot a 26 inch wheel apart from a 27.5 one, but it is more easier to distinguish a 27.5 inch wheel from a 29 inch wheel.  The 29 inch wheel offers more comfort and when it comes to passing over different obstacles does much better  then the 26 or 27.5 inch wheels.

However the 27.5 inch comes as a salvation for those not sure which is the right bike from them, a 26er or a 29er, and this is what will make this niche work. In time, bike manufacturers will offer wider ranges of components and even if Scott immediately adopted the new format, stating that the classical wheel is already… dead, 26 inch bikes will keep on rolling long time from now on.

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