The Power Tap G3 MTB Disc hub finally allows mountain bikers to utilize power analysis during their singletrack rides. This beefier version of the road hub is specifically designed for the abuse that mountain bikers dish out, and built to be paired with a standard 160mm mountain bike disc brake rotor. The Power Tap G3 features a 74mm diameter and a 15mm alloy axle. The stiffness to weight ratio is incredible. The total weight is about 680 grams, but that includes the 160mm rotor. The system relies on eight strain gauges, which yield measurements within 1. 5%. Of course, Power Tap built the electronics into the end cap, so you don't have to dismantle the wheel to service the brain. The whole thing is powered by a single CR2032 watch battery, which will last for approximately 300 hours of riding. As is the standard, the G3 is equipped with an ANT wireless transmitter that sends power, torque, speed, and virtual cadence data to either PowerTap's Joule or any computer unit that translates ANT It doesn't work with Yellow CPUs. The G3 is capable of storing up to 15 hours of data in one second gathering intervals, and up to 30 hours of data in two second gathering intervals.