And I quote: "Zipp wisely uses older, less-expensive builds of their rims rather than designing something new. These are the 4-piece 303 and 404 rims from the era of pre-dimpled Zipp rims, which are much simpler than the 30 some-odd piece builds of Zipp rims today. The rims start with an ultra-light aluminum rim that is bonded to a structural carbon shape; the two segments work together. Depending on what test data you read, the older rims are either nearly as fast or slightly faster than the new ones. Flash Points aren't the only wheels with these rims; this is the only one that's built by Zipp in Indiana."