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An introduction to 650b (27.5") wheels


MTB wheel size comparison

It doesn't seem all that long ago that the MTB world was awash with stirrings surrounding a new wheel size; it was called the 29er. Many years on and it seems every trail ride I go on, my 26" wheeled dually stands out in its "old-fashionedness" (excuse the invented word). It has become the exception not the norm.

This year the stirrings have started again and another wheel size is being released just to add a little more confusion: this one is called the 650b or 27.5" wheel. It is not actually a new size, the 650b has been around for decades in various forms, only now is it being marketed as a necessary new size for mountain biking.


FACT:  Wheel size denotes the approximate diameter of your MTB wheels measured from the outer edge of the tire. Obviously this is an approximate size as tires come in many different profiles and bag sizes. A chunky, high profile, big bag 26" tire could almost qualify as 27.5" diameter.


MTB wheel size comparisonMarketing gone mad?

So why a new size? Do we need 3 wheel/tire options for mountain biking? Someone thought the market was missing a wheel between 26" and 29". I do find it a little odd that we need an in-between size, and as an ex-bikeshop guy I can't help but feel sorry for the brick and mortar retailers who now have another product to stock and supply components for.

It is exciting as a rider and consumer to have multiple choices, but one does end up feeling like a pawn in a game, when being provided with choices we never really needed to have. The market tells us what we want, rather than the riders asking for it.

Personally I can see the purpose of the fact my next purchase will be a 29er hardtail. The 29er is a completely different bike to a 26" and for that reason has a different purpose. But 27.5"? It seems so close to the 26" to not make a lot of sense, and with some manufacturers claiming you can put the 27.5" wheels and tires on a 26" frame...not sure I would trust that?

One reason could be that 29" wheels and big travel gravity frames (like down hill bikes) do not really sit well together. The 650b could be the perfect size for these MTB's, with the benefits of both 26" and 29er.

I acknowledge that I will never know personally until actually riding one, but from all reports the differences are so marginal that you need to ride both in the same session to really feel the difference. Marginal gains are fine for Team Sky but the average punter on whom the marketing is aimed?


benefits of MTB tyre sizes

"Jack of all trades, master of none"

So, what are the benefits?

  • Superior acceleration and nimbleness of the 26" wheel, yet with some of the better rolling characteristics and grip of a 29er.
  • A better option for short riders. 29ers were always a bit of a stretch for the height challenged rider with a 'perched on top' feel. 650b may offer an alternative for these riders.
  • Geometry and frame construction issues have been a problem when fitting 29" wheels on bigger travel gravity bikes. 650b could be a new standard for downhill and freeride applications.
  • 650b wheels will be lighter and stronger than 29ers. Will it make a difference with so many XC racers using 29ers now? Time will tell.

So, is this the end of the 26" MTB bike? Maybe. It certainly won't happen overnight as the 26" MTB has been around for 30 years. Eventually though I can see hardtails, XC and trail platforms will be 29er and freeride and gravity bikes perhaps will adopt the 650b as a new standard.

Have you ridden a 650b? Share your experience with us in the comments below...



ProfileAuthor: Christian Woodcock
Christian loves riding bikes. He has many years experience working in bike shops and has raced mountain bikes at a high level with success. These days expect to see him climbing and suffering on a road bike, or talking it up on the trails with mates.

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