Dan Bigham's hierarchy of aero gains: position (40-80W saving), skinsuit vs loose jersey (10-20W), aero helmet (5-10W), deep-section wheels (3-8W), aero frame (1-3W). Most amateurs invest in the wrong order — buying aero wheels before fixing their position. A proper bike fit that lowers the frontal area is worth more than any equipment change. CdA (drag coefficient × frontal area) is the metric; lower is better.