What is a Bike Power Meter?
Power Meter Basics
A power meter is a device that can measure the power output of a cyclist.
Using a power meter, a cyclist can get instant feedback and measurements by way of a handlebar-mounted computer.
The computer can display exactly how much power a cyclist is producing at any given moment as well as provide an average over time.
Unlike speed, power is not affected by hills, wind, terrain, or other environmental factors.
Power is typically measured in watts, and a power meter gets that measurement by taking the torque produced by your pedaling and multiplying it by your cadence (how fast you pedal).
A basic unit of power equal to 1 joule per second. A common unit used to express effort or intensity amongst cyclists.
The amount of work done or energy released in a measured time frame, normally expressed as a watt. For a moving bicycle, Power = Torque (how hard you pedal) × Cadence (how fast you pedal).
Why train with a power meter?
Most training systems only allow you to measure your body’s response to the work. The actual amount of work you perform remains a mystery – or at best an estimate. When power is measured, your training becomes much more effective.
Heart rate and your own perceived exertion is the best way to measure your body's response.
- Power is the best way to measure intensity and work.
Why is this a problem?
Not having a constant measure of power results in:
- Too much work, meaning injury and overtraining risk.
- Too little work, meaning you’re not getting the maximum benefits you want.
Having a constant measure of power helps you:
- Establish your baseline fitness
- Accurately measure even the smallest fitness gains
- Accurately measure energy use for nutrition planning
- Quantify intensity, duration and frequency instead of guessing
- Prevent overtraining
- Pace properly for time trials or set yourself up for a successful run
Related: Triathlete Jim Rosen discusses even more benefits of training with power in Why I Train with Power.
How accurate are power meters?
The PowerTap is one of only two power meter companies, which has been scientifically researched and 3rd party validated by Allen Lim (co-founder of Skratch Labs) and other researchers at the University of Colorado – Boulder.
Validity and Reliability
The researchers in Colorado were some of the first to validate PowerTap power measurement. They tested the reliability and dependability of the hub and found it to be +/- 1.5% accurate, time and time again.
The PowerTap pedal and chainring power meters are validated by comparing with a PowerTap hub, and have been proven to show the same amount of accuracy and consistency, +/- 1.5%.
We've collected a few examples of scientific research here to prove it, not something every power meter company can do:
- Accuracy of Cycling Power Meters Against a Mathematical Model of Treadmill Cycling
Study published by the International Journal of Sports Medicine
- Accuracy of SRM and PowerTap Power Monitoring Systems for Bicycling
Study published by Medicine & Science in Sports & Exercise
- Validity and Reproducibility of the PowerTap P1 Power Meter when Compared with the SRM Device
Research presented at the International Conference of Science and Cycling
Power data is transmitted wirelessly, and there are two flavors of technology:
ANT+ is a 2.4 GHz wireless network, which is used to send standard information wirelessly from one device to another.
ANT+ allows two different wireless devices to understand one another, even if the two devices are from two different manufacturers. Communication can be between power meters, speed and cadence sensors, and heart rate monitors.
Bluetooth Low Energy
Bluetooth Low Energy (also known as Bluetooth SMART, Bluetooth 4.0, or simply BLE) is low power wireless technology.
Bluetooth allows devices to wirelessly connect with applications via your smart phone or tablet devices.
To learn more about ANT+ and Bluetooth, watch as PowerTap's chief electrical engineer discusses the differences:
Using a power meter for the first time can be overwhelming. You're excited to use your new device, but now what? We'll cover the basics of how to begin using it effectively.