If it is not enough to have the recent 27.5″ wheel standard, the world of wheels is about to get another new standard. The 650b+ or 27.5+. It’s not really a completely new format but an adaptation of the 27.5″ standard. There are a few companies testing at the moment with a few prototypes for the last few months.
If the 27.5″ has just been adopted as the in between size of 26″ and 29″, the 27.5″+ could be considered the mid point of Fat Bikes and normal Mountain Bikes, some are even referring to it as Semi Fat. In this case the line of thought is that designers are looking for another evolution that will bring with it advantages and or it might just be an experiment that will be forgotten.
In principle the people pushing this new standard are WTB and Rocky Mountain. They are working together to see what the value of this new wheel size could be. Trek have also demonstrated interest, with one Italian company Gas29 already developing and frame dedicated to the new size, the Rovagrossa 650b+.
In practical terms the 27.5″+ is a wider 27.5″ tyre. An intermediate size tyre between a Fat Bike tyre and a traditional 27.5″ tyre. The tyre chamber size is around 2.8″ to 3.0″, therefore a rim with a greater internal width is needed, around 40mm to 45mm. With these dimensions a 27.5″ tyre is actually the same diameter as a normal 29″ but with a greater air volume, essentially a Fat tyre, they seem to have created a Frankenstein tyre. The 27.5″+ wheels will probably fit in some frames and forks on 27.5″ bikes and 29″ bikes, but probably frames adapted specifically for this new standard with dedicated geometry will be developed to ensure the wheel clearance and the Q factor are respected.
At this point, respecting the “middle is better” theory, it would be fine to have a wheel that, within the wider tyre idea, reaches the diameter of a normal 650b tyre. This could ironically finish in the hypothesis that 26″ might return as 26″+. Some people might remember the Nokian Gazzaloddi in 3.0″ mounted on Sun Rims Double Wide rims…