With no moving parts, and everything protected by our high-strength ABS-PC housing, the Stages Power meter preserves the structural integrity of the crank—all while seamlessly adding the ability to measure your power.
TINY: 65mm x 30mm x 10mm
Under 20g: less than an energy gel
Swapping a Stages Power meter from bike to bike is as simple as changing the left crank arm—making it possible to have power across multiple bikes.
With no external or moving parts, a waterproof housing, and a user-replaceable battery, Stages Power meters handle all weather conditions and all riding styles.
Power is a measurement of the work you do on the bike, and the most accurate way to measure your effort. Unlike your heart rate, which can be widely affected by physiological influences, including: stress, lack of sleep, caffeine, temperature, time of day, dehydration and other factors, power shows exactly how much work you are doing and exactly what you are getting out of your training. Power is the perfect tool to understand how you are progressing and the best indicator of fitness gained and fatigue level. Simply put, if you want to know how you’re doing, check your power.
The equation for power is pure physics:
POWER = TORQUE x CADENCE
P = 2X[(F x 9.8 x L) x (R x .1047)]
P=Power, aka Watts.
TORQUE // Fave x 9.8 x L = Torque
(Fave = Average Force per Revolution )x(9.8 = gravitational constant)x (L=Length of Crank)*
To measure TORQUE, Stages’ proprietary strain gages are laid precisely along the crank arm. These gages, which are the same tool used in aerospace, can detect the smallest flex in the stiffest crank. In this case, every pedal stroke, causes a small amount of flex along the crank arm. This downward force happens in every rotation. This force, multiplied by 9.8m/s2 and the length of crank arm are used to determine the force applied to a pedal stroke, or torque.
CADENCE // R x .1047 = Cadence
(R= Rotations — measured using an accelerometer*)
Using an accelerometer (the same technology used to tell your smart phone how to orient its screen), the Stages meter measures cadence. The proprietary circuitry houses this cadence tool, allowing the meter to eliminate the antiquated need of magnets, external sensors, cables and zip ties to measure cadence. This modern technology also allows the meter to capture multiple positions per revolution, resulting in a faster response and better overall data.
Once Cadence and Torque are collected, they are multiplied together to determine the POWER of a single pedal stroke. We then multiply this number by 2 with the assumption of doubling the left leg power. This one assumption, that both legs produce relatively the same force, is the key factor that allows Stages Power to be more compact, lighter, more robust, and more economical than any other power meter on the market. This assumption has been fair and consistent for most of the riders on the road.
Measuring power is simple in a controlled environment, but when you’re out in the elements facing varying climates everything changes. The strain gages used to determine power, whether it be crank based, spider-based, pedal based, etceteras, are highly affected by changes in temperature. If a power meter system does not take into consideration changing temperatures throughout a ride, power will be wildly inaccurate.
Why do changing temperatures affect power? Strain gages are tiny metallic wires laid across a metal crank, spider, pedal etc. It is the flexing of these wires that measure torque. When these wires heat up or cool down in response to external temperatures they naturally expand and contract. This results in false data.
Stages Power meters are equipped with ATC – [Active Temperature Compensation]. Different temperatures cause strain gages to expand and contract a specific amount. ATC allows the power meter to compensate for temperature changes that would otherwise affect the strain gages and their ability to accurately measure force. More importantly, Stages ATC auto-adjusts on the fly, without the need to stop pedaling.
The Stages Power meter is the first power meter to use Bluetooth Smart protocol in addition to ANT+.
ANT+ is the gold standard for over-the-air communication in the cycling and athletic industries. The system is simple, robust, and provides for riders the ability to add power to their ANT+ devices.