Gates recently released their Carbon Drive Calculator (CDC) for the iPhone. The CDC just might be the ultimate app for the combo tech-nerd/bike-geeks in the crowd. Besides calculating center distance, drive speed ratios, and optimum pulley size, the app uses the iPhone microphone to test belt tension. Yup, believe it or not, you pluck the belt like a string and the CDC estimates belt tension by pitch. I haven’t tested it yet (I’m not an iPhone user), but it sounds way cool if it actually works. If there are any iPhone users in the crowd who also run a Gates Carbon Drive, I’d love to hear how it works for you.