Power meters are no longer reserved for professional cyclists. In recent years, a dozen companies have jumped into the game, driving down prices and greatly increasing consumer choice.
But how do they work, why do you need one, and, once you’ve made your decision to invest in one, what should you be looking for in a power meter? We answer those questions here.
Related: Best power meters
How do power meters work?
Power meters typically work by measuring the force on a component (hub, pedal axle, crank arm, spider) using strain gauges. They then convert this to power by multiplying it by the angular velocity of that component. Power is measured in watts.
They transmit this data wirelessly to a head unit such as a Garmin Edge, Wahoo, Elemnt, CyleOps Joule via the ANT+ wireless frequency. Many newer power meters also have Bluetooth, so you can pair with your smartphone. In addition to displaying power as you ride — in a variety of options, from live to 3sec average to 10sec average to left/right balance on some units — the data can be uploaded to various sites or apps for post-ride analysis.
Most power meters are relatively easy to use: you pair them with your head unit the first time you use it, then just ride. On subsequent rides, your head unit will remember the power meter and deliver data as soon as you start riding.
Why training with power meters is essential
Power meters help you measure your fitness by telling you how much power you’re putting out, regardless of temperature, wind, weight and bike type. If you’re training, they’ll help you know if you’re training effectively if you’re increasing your wattage over time. A speedometer can’t do this, neither can a heart rate monitor.
A good power meter therefore needs to give consistently accurate and precise data. If you’re measuring small changes in your fitness, then you need to know your numbers within a few watts. Those numbers need to be repeatable if you change power meters, otherwise you won’t be sure whether it’s your training giving you amazing numbers or a wonky factory calibration.
How to choose a power meter
There are various factors to consider when choosing which power meter to buy. Here are four questions to ask yourself.
1. Are you a professional rider?
If so, then you will have to use whatever your team hands you. If not, good news! You can pick whatever you like! Take a look at our Best power meters article to see which of the latest power meters scored most highly in our recent tests. If you want to drill into it, you can look at some comparative data files for the meters in this roundup in their respective reviews. If not, know that a power meter is just a tool like a bathroom scale or a heart-rate monitor; it’s what you do with it that matters.
2. What can you afford?
This is the biggest factor for most of us. Sure, an SRM would be great, but for most riders it simply isn’t in the cards. More than a decade ago, I bought a wired PowerTap built into an aluminum Bontrager Aero clincher wheelset so I could train and race on a single wheelset and have power data and – key point here – it was the most I could afford. Today there are more choices. Not that they are cheap, but Stages, PowerTap, Pioneer and 4iiii now have some solid offerings at prices that won’t result in threats of divorce from your significant other.
3. Where do you want the meter to be? Or, more to the point, what is least inconvenient for you?
The second-biggest factor in picking a power meter is considering your type(s) of riding and your type(s) of bike. The one-road-bike rider has it the easiest; someone with a road bike and a tri bike or a cyclocross bike or a second road bike in the stable has more logistics to sort out.
A set of Garmin Vector or PowerTap P1 pedals can move fairly easily between the road and TT/tri bikes, but the ’cross bike is out of the picture, and you’ll probably want to put Look-compatible pedals on the other bikes. (Otherwise, you’ll either need two pairs of cleated shoes or you’ll have to move and then calibrate the pedals every time you hop on another bike.) A PowerTap wheel can move easily between all these bikes, but then what type of wheel will you get?
The Stages, 4iiii and Pioneer left-arm meters can be moved between bikes with Shimano cranks. And, technically, you can move complete cranks like SRM and Quarq — but that’s not realistic.
If you are committed to a single bike, however, a crankset-based system can be a great way to go, freeing you up to pick or swap pedals and wheels as you like. Plus, this option can give you left/ride data and a complete power picture compared to the left-only systems.
4. What will work with what you have?
Even if you are a one-bike rider, make sure that the power meter you’re considering is compatible with your bike. For crank-based systems, bottom bracket solutions can be had – to a point. Double check with the power-meter company or your local shop before you purchase.
Key features of a power meter
Any good power meter should have the following features:
ANT+ is a wireless data communication protocol that’s used to send data to a recording device, such as a Garmin or some smartphones. Most power meters use ANT+, while some also use ANT or Bluetooth (for sending to smartphones). ANT and ANT+ are owned by Dynastream Innovations, a subsidiary of Garmin.
Most power meters require you to perform a zero offset before each ride, so they know to report zero when no torque is being applied to the pedals. It’s not strictly a calibration – despite what Garmin head units say – it’s more like taring a set of scales.
Because a power meter’s sensitive strain gauges are incorporated into components (cranks, spiders, hubs, pedals), which can heat or cool during a ride, it’s vital that the power meter can adjust to this on the fly. Otherwise the readings will drift with changing temperatures, resulting in a loss of accuracy.
Some power meters measure the relative contributions of your left and right legs to your total power output. This can be useful in correcting a poor pedal stroke.