Originally Posted by
B. Carfree
Wide is a relative term. In racing, wide is 25 mm and the reasoning, with some data, is that a closer match between the rim width and the tire both improves aerodynamics, not really a factor in touring, and reduces rolling resistance by reduced sidewall bulging.
The real reason for the current wide-rim trend (which I think is here to stay) is improved tire shape, and subsequently better ride and handling. The evidence on aerodynamics is mixed, but even if it's actually faster, aerodynamics wasn't the motivation to introduce wider rims for road racing.
My own experience is that wide tires at low pressures (cyclocross) benefit a lot from the wider rim. Even at the higher pressures you would use for touring on the road, I think the benefits are still noticeable. 19mm is really too narrow a rim for a 32mm tire. It works, obviously, but a touring rim like the Dyad - which is actually lighter than the Deep-V - is a better choice.