Made an interesting observation yesterday re above and thought I'd like to share. My usual string and tension setup is zymax 67 at 21lbs, since I play with plastic birds. At this tension, the dominant frequency with my iPhone app is 940Hz. Now this was the perfect setup on my mx80 in May when the playing temperature was around 16-18 Celsius. Great touch/feel, power, control, response. Fast forward to yesterday with the playing temp around 25 Celsius, and the strings feel completely spongy. No feel, control or response, and there was a drop in power. The string frequency is only slightly lower at 930Hz, which is not much of a tension change since I know from experience that 1lb is around 60Hz. (Yes, zymax strings really hold their tension well!) So, then I switched mid game to my T2 with the same string at 23lbs and everything was all good again! Touch/feel, control, power, response was back! And the funny thing was that I couldn't play with this tension back in May when it was cooler because it felt too tight and brittle! I checked the frequency and it hasn't changed from 1050Hz from then till now, so the tension is the same since I haven't used it much as the mx80 is my main racket. NB: all my rackets are strung by the same reputable and very experienced stringer on his ECP machine. So, my theory is that the change in temperature doesn't affect string tension much, if at all, but it does affect the string's physical properties such that it'll feel spongier when warmer and brittle when cooler, despite no noticeable change in tension. This may explain why our friends in tropical climes like Malaysia and Singapore prefer 28-30lbs tension, while Canadians and Europeans in northern climes like it lower at 24-26lbs, both playing with feathers.