I've never really quite "gotten it" until now, when I finally decided come hell or high water I was going to figure out why peak power is after peak torque, when one can be calculated directly from the other. Now that I understand, it's really not that hard. Torque is the force applied to something to make it turn, while power is an amount of work (such as moving a certain weight a certain distance) performed in a certain time - best described by examples: Imagine a steel rod, half an inch thick, with an infinitely strong metal wire wrapped around is so that pulling on the wire will unravel it and cause the rod to turn. An elephant pulling on the wire creates a huge amount of torque - you'd have no hope of holding the rod with your hand to stop it (slowly) spinning - but very little power. Since the maximum RPM of my elephant engine is very low, a massive gear will be needed to get the RPM up high enough to start generating reasonable power. As always, there's the formula: HP = Torque (ft-lb)*RPM / 5250. What this means is that low torque is fine providing you have high RPM, and low RPM is fine if have high torque. You can always use gearing to get more RPM (and therefore more power), but while a higher ratio gear accelerates quick, it's speed at the engine's redline is slow - you run out of gear fast! So more torque from the engine also means less gear changing. Chances are you already knew that, I did - but here's the kicker: Why is peak power output AFTER peak torque output? Well the answer is more obvious than I realised. Once you hit peak torque (say, 11,000RPM), going to 11,500 means you have a little less torque BUT FAR MORE RPM, so power continues to rise. At 12,000, RPM is even higher but now the quickly decreasing torque is starting to take it's toll and the power flattens off. Any more RPM and the torque losses exceed the RPM gains. Moral of the story: change after peak power, not peak torque.