Zipp built the 303 SW Carbon Tubeless Disc rear wheel around a 40mm hookless carbon rim that takes its design cues from the gravel-specific 303 XPLR . Internal width measures 25mm and external width 33mm, with wide uprights meant to minimize pinch flats . Zipp revised the carbon layup for this generation, raising impact strength by roughly 10 percent without adding grams . The result is a road wheel with enough structure behind it for gravel, cobbles, and cyclocross as well as pavement.

Tire sizing drives the aerodynamics here. The 303 SW is optimized for tires 30 to 35mm in width , which is where casing and rim form a continuous shape instead of the lightbulb bulge that appears when wide rubber sits on a narrow bed. The 25mm internal width is designed around those sizes at lower pressures, increasing tire volume and smoothing the ride . Testers have noted composure in gusts, with the wheels holding their line even when hit by strong crosswinds .

Hookless construction means tubeless tires only , and pressure ceilings scale with tire width: 65 psi for 30-34mm, 58 psi for 35-39mm, and 51 psi for 40-44mm . One detail is worth knowing before the first setup. The sealant injector supplied with the wheels routes sealant past the AXS Wheel Sensor; injecting sealant without it floods the sensor and can damage it beyond use. Keep that injector with your tubeless kit rather than in the box.... Read More