650b versus 29er – What’s the deal?

The latest and greatest in the MTB arena is the 650b wheel size. This is an old European standard originally used for touring or city bikes. It is smaller than the 700c road wheel that has been adopted by the mountain bikes to create the 29er bike. Yes, a road bike rim is the same size as a 29er rim. The smaller 650b rim was used in conjunction with a 30-40c tire to create essentially the same diameter as a road wheel with a 23c tire. This resulted in a smoother ride, better for city or rough terrain, and didn’t affect gearing. (Bigger wheels effectively raise the gearing, making it harder to pedal the same gear as on a smaller wheeled bike. This is confusing!)

So why has a rim size that is in between 2 well-established wheel sizes been introduced? The answer is not so simple. It is partially due to marketing and is sales driven. Bikers want the latest and greatest products. It’s also part design. Engineers who struggled to fit 29er rims in a full-suspension platform now have the luxury of shrinking the wheel size to shorten the wheelbase, lighten the bike, provide more travel and increase clearances. Finally, I believe the riders who adopted 29 because of it’s advantages slowly became aware of it’s drawbacks. And skilled riders, who can appreciate nuances, found something different in the 650b. Just like a skilled golfer has specific clubs for specific tasks, so goes the mountain bike rider. The 29er shines in rock gardens flying over the top of everything. Provide horse-power and you are golden. Log overs be dammed. I can easily ride over a log (that I have never encountered previously) 2 feet high or less.  Descending on bumpy ground is another ideal scenario for 29. The wheels stay on top and momentum does the rest. However, tight twisty single track slows the bike down. 29ers have a long wheel base and a larger gyroscopic effect when steering. Turn initiation is harder especially at speed. Because the larger wheel has more momentum it loves flying straight. Slight steering modifications take more input. Also, with a long chainstay, you cannot hop the bike around turns or shift the bike as easily as a smaller wheeled bike. Just think of BMX tricks. Riders can routinely spin 20″ wheeled bikes around like a top. There is a noticeable improvement with steering when I rode a 640b bike. Descending was better also since I could more easily select my line. Finally I wanted to mention wheel flex. All mountain bike wheels take a beating. The 29er wheel has the most flex and experiences the highest side-to-side forces since it has the longest spokes and largest leverage forces from the ground up. The result industry-wide has been trashed rear wheels and free hub bodies. Shrinking the wheel makes it stronger and more durable and that makes a happy customer.

So what about the ride? Overall my personal impression was FUN! I was shocked how different it was from my 29er. It was easy to ride and to point and to turn. It was nimble and quick. The small wheel accelerated quickly. Riding hard up short steep sections was a breeze. It descended great and was fast in smooth twisty singletrack.  It was an excellent tool for the trails and a skilled rider can appreciate the bike (and wheel size) as a specific tool to be utilized. As a framebuilder the smaller wheel size is easier for design purposes and construction is no problem.

So it looks like the 650b has found a place but 3 wheels sizes? Is this the new standard for the mountain bike sector? No. Product managers have left the 26″ wheel to low-end hardtail bikes. Mid and upper end will only be offered in 650b and 29. With all the existing 26″ bikes still in the marketplace it will take decades to eliminate them. Here at the shop, we still carry 27″ tires for bikes over 20 years old.