Can someone explain to me why there are sometimes fairly large variations in recommended string tension between two racquets that are very similar. For example, the Prince Shark and Prince Air DB are by many measures very similar sticks (TW even lists each racquet on the other's "Racquets similar to" list). But, and here's what I don't understand, the rec. tension for the Shark MP is 43-60 (45-62 for the OS) while the rec. tension for the Air DB MP is 53-63 (and 57-67 for the OS). That seems like a big difference for what can arguably be seen as two racquets that are very similar. What's going on? Thanks in advance for any light you can shine on this for me. Tennis--cheaper than therapy and more effective.