Zipp put out a new generation of one of their most popular wheelsets. They're fat and hookless. New hubs.

While external width is only 1mm wider at 30mm, the rims use a hookless sidewall design that gives a 25mm bed and a much fuller tyre profile. This reduces the ‘waist’ between tyre and rim that could often trip up airflow and while the new wheel is 5mm shallower than the old 303 at 40mm deep, it’s actually tested faster in the wind tunnel and on the road.

The take-home is that using Zipp’s own 28mm tubeless road tyres showed that on rough/gravel/cobbled roads, a 70kg rider will roll fastest with 55psi in the front and 60psi in the rear. Using a 30mm you should drop to 50-55psi and even lower the fatter you go. Even on smoother roads, Zipp’s data suggests you only need a handful more psi to return a 10W gain over narrower rims and tyres at higher pressures. They’ve even deliberately rated the rims with a max of 72psi, not because more isn’t safer but because they’re determined to get people to try lower pressures.

https://www.cyclingnews.com/amp/news...st-303-wheels/