When Castelli engineered the first aero jersey for road racing back in 2006, everyone thought we were crazy, even a few of the pro riders. Back then, aero was only for TTs. Performance clothing meant moisture management. And you could win the Tour de France with a baggy jersey that was little more than a polyester T-shirt with pockets on the back. Even our aerodynamic consultants expected limited, if any, gains, so we named the jersey the Split Second. In the end, the gains were pretty substantial, and we completely revolutionized the look of the pro peloton. We're now on the seventh major revision of that jersey, and we've found even more gains. Still heavily benefitting from CFD analysis of wake flow in the riding position for fabric and seam placement, along with pro rider feedback, this jersey is both fast and comfortable for long days in the saddle. And for those days when it really matters, wear our Bolero SS base layer under the jersey for even larger aero gains.