By controlling airflow around the back half of the wheel 404 firecrest is 9 seconds faster than its predecessor 404 model over 40 km at a moderate 10 degree wind angle at higher wind angles the improvements are even more dramatic in terms of speed and stability thats because firecrest moves the centre of pressure closer to the steering axis so crosswinds exert less side force on the wheel the result is a more stable ride firecrest174 a better wheel in every way zipp39s proprieta