Castelli's Free AR 4. 0 Jersey is designed with one thing in mind aerodynamics. And, although its performance has since been surpassed by the Race 5. 0 version, the 4. 0 is still a very nice jersey that'll save you 12 watts at 40kph. The Free AR 4. 0 Jersey is cut with the contours of the body in the cycling position in mind. You won't hear any flapping, to be sure, and after a while, you may hardly notice you have a jersey on. It just feels right. There's no bunching when you're in the drops, and the sleeves won't ride up. Fair warning, the Free AR 4. 0 won't look or feel right when you're standing around, drinking coffee and waiting for the ride to start. Given the in saddle fit, though, that's a tradeoff we're happy to take.