Why do aero race jerseys have such long sleeves?

The extended sleeves are the single most impactful aero feature of the jersey. By covering the upper arm and terminating with a silicone gripper at the widest part of the deltoid, the sleeve smooths the transition from torso to arm, eliminating the turbulent airflow and fabric flutter that occurs with traditional shorter sleeves. Wind tunnel testing shows this feature alone can save 3-8 watts at race speeds. The silicone gripper is essential — without it, the sleeve would ride up and negate the aero benefit.