Zipp's 404 family spans the full depth of the brand's wheel lineup, and the 404 S rear wheel occupies the shallow end of that range at 50mm of carbon rim depth. Where the 404 Firecrest commits to 58mm with ABLC dimple treatment for outright aerodynamic drag reduction, the 404 S from Zipp takes a more restrained approach — a smooth rim surface and reduced depth that trades a measure of flat-road aero performance for a lighter-handling, more crosswind-friendly ride. The hookless Tubeless Straight Side rim construction narrows the tire-to-rim junction for a cleaner aerodynamic transition, and the tubeless-only compatibility means clincher tires with inner tubes are not an option here.

The symmetrical rim profile supports tire widths from 28mm through 39mm, which gives the 404 S rear wheel enough range to cover road duties while stretching into mixed-surface territory when paired with wider rubber. Running wider tires at lower pressures on a hookless rim reduces rolling resistance on imperfect pavement and improves grip through corners — a compounding advantage over the course of a long road race, gran fondo, or gravel-adjacent route. The UD carbon fiber finish with adhesive decals keeps the aesthetic clean without adding the weight of a painted surface, and the dark grey decal colorway blends into the carbon weave rather than announcing itself.

Zipp builds the 404 S rear wheel with a 24-spoke count in a 2-cross lacing pattern using Sapim CX-Sprint spokes and aluminum nipples with Sapim Secure-Loc anti-rotation features. The higher spoke count compared to a 20-spoke front build adds lateral stiffness and load-bearing capacity where the drivetrain forces concentrate — a deliberate choice for the wheel that absorbs pedaling torque and cassette loads. The 176D hub spins on stainless steel cartridge bearings with aluminum axles, and the rear wheel ships in either SRAM/Shimano HG or SRAM XDR freehub configurations, so match the driver body to your cassette standard before ordering. The 12x148mm thru-axle spacing is the Boost standard, so confirm your frame's rear dropout width before purchasing — this is not the 12x142mm spacing found on most road disc frames.... Read More