The 27.5in wheel size was to some extent quite an obvious development, but it was also the first true innovation in wheel size on mainstream bicycles for a very long time. And the results have been rather impressive.
The reason why so many people have adopted this new format is because it really does combine the best qualities of 26in and 29ers. Bikes with 27.5in wheels get up to speed quite nicely. They roll well, and can take on trail obstacles without losing too much composure. The 27.5in tyre grips well, too.
But more than the benefits of the 27.5in wheels, their real beauty is that you don’t have to face any of the bigger compromises of the other wheel formats. You don’t feel so high and removed from the action as on a 29er, but you also don’t feel quite as nervous in the saddle as with a more reactive 26in wheel bike. Bikes with 27.5in wheels aren’t as heavy as 29ers, but they’re more stable than 26in wheel bikes.
The biggest negative is that 650b is still a relatively new format, so you’d expect spare or replacement parts to be not quite so abundant as the longer-established sizes. But 27.5in wheels have been embraced so quickly by the bike trade, even this isn’t a major problem.
So what’s the big deal about 1.5 inches less or more? Actually, it can make all the difference.