Thinking Out Loud About: Where Does 27.5″ Fit?- by c_g and Guitar Ted

Last time we took a look at the “middle child” wheel format for mountain bikes was in April when we were pointing out that a resurgence of 27.5″ wheels was upon us. (By the way, we’re joining a growing number of folks that are proposing that the moniker “650B” be dropped for these fat tired wheels since we are talking about mountain biking, not rando/camping bikes here.) Well, you can catch up with all of that here.

While much of the product for 27.5″ has yet to be revealed, much less available to ride, Twenty Nine Inches’ own c_g has not been idle. He has been busily testing product in a couple of ways to first sus out the advantages/disadvantages between all three mountain bike wheel standards.

26", 27.5", and 29" wheels

c_g has assembled a stable of wheels that are as similar as possible to test on a hard tail platform. In fact, the wheels are absolutely identical and were provided by TUNE (www.tune.de) as were the tires by WTB, cassettes and rotors by SRAM. While it may be that some 27.5″ bikes will be hard tail/XC bikes, it is being positioned in the market as a 150-170mm full suspension wheel size, for the most part. That said, c_g felt it was a more “pure” test platform on a rigid hard tail. The variable of suspension being removed, he could then focus on the characteristics of the wheels themselves.

c_g's personal Kona King Kahuna w/27.5"ers fitted

Here is some commentary by c_g concerning how he found each wheel size to work on his bike:

26 Inch: I spent a full week on them, only to get accustomed to them again and not to be blamed I had not given them a real chance ;). It was definitely amazing how easy they picked up speed (in the week I have riddden them I found myslef sprinting up the slopes more often, than ever :)), -> My opinion: Unless sprint properties and acceleration are on the top of your list, I tend to call riding a 26 ” rigid bike a penalty – at least if one wants to go on real trails.

27.5 Inch: It became apparent already on the first trail meters, that the roll-over ability is much better than the 26-inch model. Strangely I also found the the playfullness of the bike and advantages in acceleration to be preserved to a large extent.

29 Inch: -> When it comes to long trips or for their roll-over ability in technical terrain, I would never trade in 29″er wheels – but the gap to 27.5″ wheels is (for me) much less than I had expected. Where the 27.5″ wheel is definitely better is at acceleration and keeping a sense of nimbleness/playfulness on the bike.

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So there were c_g’s first impressions. Then he moved to a front suspended bike and has spent more time with 27.5″ers. This was on a recently tested Bergamont hard tail bike.
The Bergamont was ridden back-to-back on the same trails with both 29 and 27.5″ wheels. After doing several rides, here are c_g’s impressions on this configuration…

The results have been as follows:
• The difference in ride feel between the 29 “wheels and 27.5″ was still detectable under regular riding, but the suspension fork slightly covered over the difference, that was more apparent on the previously ridden rigid bike. The differences primarily showed when pushing the limits or when riding rough grounds seated.
• The 29″ers felt better wherever roll-over ability and traction had been key, the 27.5″ format primarily had the rapid acceleration to bring to the table.
• Subjectively, the 27.5″ wheels felt slightly stiffer (and more precise), but this was offset by the lesser braking traction and cornering grip.
• On a few of the shorter tests I did time myself (with pulse control) and the results had been so close, that no format came out as a clear winner.

What caught my attention though was how riding style impacted how each configuration felt:
• If you drive mostly in a sitting position, remain centered in corners and prefer a not-too-dynamic riding style in the rough – then the 29″ers do have a clear advantage. Here the benefits of 27.5″ cannot overcome the shortcomings at all and the roll-over ability weighs more than improved agility and acceleration. Typical applications for this riding style would be endurance racing, marathons and classic MTB touring.
• If, however, you have a a very active riding style with lots of movement on the bike, if you like riding out of the saddle, push your bike into corners – then the 27.5″ is at least equally fun to ride. Then the lesser traction and grip are outweighed by the better flick-ability and more agile handling. I can ride this way but usually find it draining my body more quickly.

A few years ago the desire for a more agile 29″er may have been halfway justified, but with the latest generation of XC 29″er, bikes like the BMC TE01 or BERGAMONT Revox I no longer count this a valid point. Therefore the tangible benefits of 27.5″ to me are primarily the lower wheel weight and thus easier acceleration. The question on sense and nonsense of 27.5″ for hard tails therefore points towards 27.5″ remaining a niche. By my current position I would not hesitate to purchase a 29″er hard tail if I were looking for one. The only real benefit I see in 27.5” hard tails is primarily with very small frame sizes, where a desired handling characteristic is hard or impossible to achieve with 29 inch wheels.

c-g’s INTERMEDIATE CONCLUSION: For hard tails and rigid bikes my preliminary view is that with the new generation of agile 29″er geometries the advantages of 29″er far outweigh (if not negate) the benefits of the lighter 27.5″ wheels. There may be a true benefit with very small frame sizes, but anything else in my opinion will be 29″er territory – and by what we see in industry news, pretty much every manufacturer tends to agree.

So much for now on my testing of 27.5″ on hard tails – next we will step into the realm of full-suspension bikes and will have something truly special for you coming. More on that
soon. (c_g)

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We’ll be reporting on our experiences with the 27.5″ sized wheels, which we expect will be making a big splash in Europe, and will be pushed hard for full suspension in the longer travel realm here in North America. Stay tuned for more from c_g, and reports on new introductions from Eurobike and Interbike this fall.