Zipp 303 Firecrest wheels are designed for the real world...a world of imperfect conditions and uneven surfaces. Efficiency = speed. These wheels are faster and lighter on a variety of terrains, paved or unpaved. When it comes to going fast, efficiency is reduced: wind resistance, rolling resistance, rider fatigue, weight, etc. The 303 Firecrest wheels were designed using direct measurements from the real world (as opposed to a wind tunnel or computer simulation). The results were impressive. Its rim is slightly more protruding than the previous version, with an external width of 30mm, an internal width of 25mm and a rim depth of 40mm. The profile offers low resistance and a better transition between rim and tire, increasing aerodynamic efficiency on the road.