According to Trek, the Kamm tail truncated airfoil (second from right) behaves identically to a full 8:1 cross-section (far right) and markedly better than a 3:1 section (second from left), especially at higher yaw angles. And in spite of appearances, there is no additional stub mounted to the end of the Kamm section; the airflow just makes it look like there is.

© James Huang/BikeRadar.com