26" vs 27.5" (650b) vs 29"
Andy Kessler - 23-May-2012
We're getting some questions about wheelsize, 26" vs 650b vs 29". Of course 650b is getting a lot of attention lately, and during this project we've looked at all three. The consensus in the industry at SeaOtter seemed to be that 650b is quite a popular wheel size for companies who missed the boat with 29ers and who now have a vested interest in convincing people that there is a better option. Of course, many of these people who don't really think 650b is that relevant are suppliers to the very companies pushing 650b, so nobody really wants to speak out and many are half-heartedly making some 650b product just to keep their customers happy. 

But that doesn't mean there is no case to be made for 650b! The problem is, 650b is touted as the best of both worlds when that's not really a fair assessment. Rather it's halfway in-between two worlds. It's a bit lighter than 29" and a bit heavier than 26". It rolls over obstacles better than 26" but not as good as a 29". That's simple physics, nothing anybody can do about that, no matter how much marketing you do or how many pros you sponsor with any of the three sizes. You can't have your cake and eat it too!

So in that sense, I'm not impressed with arguments that "rider X won race Y on size Z wheels, all that proves is who spends the most on sponsorships. In fact, there is a particular instance of a rider winning a big race on a 650b hardtail which is touted by proponents of that size as proof that 650b is superior. However, the rider's mechanic says the rider would actually prefer to ride a 29er but his sponsor doesn't make a good one so he is resigned to the 650b.

The weight difference between all three isn't really that large as a percentage of the overall bike+rider combo. A few hundred grams on a 70-100kg complete bike+rider weight is only 0.2-0.3% difference. The rolling difference is therefore usually bigger than the weight difference, although that's very dependent on the course. But it means that often, 29" is faster. 

However, when you get more suspension, a wheel gets over obstacles in a different way, not by lifting the bike over but by compressing the suspension. The more that happens, the less important the geometry of the wheel vs the obstacle becomes. So the 29" wheels provide the greatest advantage on frames with the least suspension, particularly hardtails.

On top of that, there are definitely situations where 29" won't work:
  1. Below a certain rider height, there isn't enough room to put the bigger wheels under the rider. So if 29" doesn't fit, then maybe 650b does, and if so that gives you better rolling than 26". Obviously, if you go further down in rider height you will even get to the point where 650b won't fit anymore, and you'll need to revert to 26".
  2. Above a certain amount of travel, there isn't space for the larger wheels. The bigger wheel also takes up more space as it travels up and down, and the more travel you have, the more difficult it becomes to construct a frame around it and position a rider on it. Making a frame with 160mm of travel using 29" wheels is very tough, and so a 650b wheel has a place there. It gives you a little bit better rolling than 26", and more space to construct your frame.
Bottomline, on a hardtail the 29" wheels give you the best rolling performance for a small weight penalty. Smaller wheels (650b or 26") will deteriorate the performance. When you add more and more travel, the rolling advantage becomes less due to the different way obstacles are crossed and on the flipside, the weight penalty gets bigger because efficient frame construction becomes a challenge.
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