Seems like the width of wheels for road cycling continues to widen every year. I bought some Boyd Carbon Clinchers a few years ago with 19 mm internal width, which at the time seemed to be on the leading edge of wide road wheels. Now, over the past month or so, Flo has increased the width of their wheels from 17 mm to 21 mm, and the new Enve and Zipp wheels are 21 mm and 23 mm, respectively.
Any thoughts on whether these wider widths are being offered because they are better for road cycling speed/comfort, or is this just an attempt to offer a more versatile wheelset for road/gravel/path even though it may cause a slight penalty on the road?
I guess ultimately I am wondering what is the best width for road cycling for those who are not going to be riding on gravel or paths?