If you're not using a power meter and tracking your watts, then you're giving the competition an advantage. SRAM's brilliantly stiff, light RED cranks feature a Quarq Power Meter integrated into the crank for easy installation, low weight, and minimal maintenance. Your power info is transmitted ANT+ wirelessly, enabling you to use the head unit of your choice (sold separately), and with no wires or external sensors, your beautifully sleek road machine stays clutter-free. Other nice features include an easily replaced battery and a wattage reading accuracy of +/- 1.5%. Also, calibration values are stoRED in the CinQo so there's no need to re-calibrate if you switch head units or swap chainrings. Plus, since the power sensor is in the crank, you can easily switch wheels. In addition, SRAM's X Glide R chainrings deliver world-class front shifts, and the oversize carbon arms transfer every watt of your strength.