Originally Posted by
WhyFi
The 303S is optimized for 28mm tires. Can't speak to the others.
The 303 Firecrest is 2mm wider than the 303S and has a minimum tire size requirement (and optimized tire size) of 28mm.
404 and 454 have the same width as the 303S (23mm internal), but Zipp says they are optimized for 25mm.