For the dozens of you lamenting the static nature of the wheel size debate over the past few years, this one's for you. WTB has announced their development of a new wheel and tire size, primarily focused at the gravel market. The new 750d
distinction is currently aimed exclusively at the custom-built-to-order market, as the diameter is large enough to require specific frame geometry.
750d is not meant to replace the tried and true 700c, but merely complement it and cater towards taller riders and those who want a more efficient ride over washboarded and rougher gravel roads. The larger wheel size is also meant to offer a larger contact patch than traditional sizing, closer in comparison to 29x2.4" mountain bike tires. Why they're not just using some of the many already available fast-rolling mountain bike tires, I don't know, but hey maybe I just don't understand innovation.
The rim designation for 750d is 660, which is 38mm larger than 622 (700c/29"), which is 38mm larger than 584 (650b/27.5").
There isn't currently any production timeline for the 750d rims and tires, so availability will be limited for the time being. WTB says aftermarket availability is contingent on OEM adoption, so if and when the drop bar world moves to adopt the new standard we may see more of these larger hoops rolling around on the gravel roads we use to get to the actually fun part of cycling.