Power meters are no longer the preserve of pro-level cyclists only. Granted, they're not cheap, but they're more readily available and slightly more affordable than they have been before.
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? Let BikeRadar answer all these questions below.
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.
They transmit this data wirelessly typically using a protocol called ANT+ – although other protocols are also used – to a head unit such as a Garmin, Joule or one of several other devices that can read the data. That's displayed as you ride and is also downloadable for later analysis.
Most power meters are relatively easy to use: you pair them with your head unit, perform a zero offset before your ride to ensure that zero pressure on the pedals equals zero watts, then ride. A zero offset is not the same as calibrating the device, which ensures power is being correctly reported throughout the range – that usually has to be done by the manufacturer.
Some meters allow you to check calibration statically, by hanging weights off the pedals and comparing them to the torque reading from the power meter. Dynamic calibration – while you’re actually pedaling – is more useful, although that has to be done on an accurately calibrated ergometer. And even then you won’t know how that translates to outdoor performance, with changes in temperature and road surface.
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:
1. Are you a professional rider?
If so, then you will almost certainly have to use whatever your team hands you. If not, good news! You're not beholden to sponsors and can pick whatever is the best for you. 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 a tool like a bathroom scale or a heart-rate monitor; it's what you do with it that matters.
After months of dorking out, we can safely conclude that running four computers on your handlebars looks ridiculous
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. Ten years 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 inexpensive by any means, but Stages and PowerTap now have some solid offerings at prices that won't result in threats of divorce.
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 ’cross bike or a second road bike in the stable has more logistics to sort out.
A set of Garmin Vector 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 clincher wheel can move easily between all these bikes, but then what type of wheel will you get?
A set of Garmin Vector pedals can move fairly easily between one or more road bikes and TT/tri bikes, but the ’cross bike is out of the picture
The Stages left-arm meter can be moved between bikes, provided those bikes have compatible crank arms. 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.
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.
Then you have the head unit to consider. Most power-meter users and potential users have an ANT+ computer on the handlebar, a Garmin Edge or something similar. Virtually all power meters work on ANT+. If you prefer to just use your phone, then you can either attach one of those goofy dongles to the bottom of your phone, or go with a Stages or a newer PowerTap that use Bluetooth.
Key features of a power meter
Any good power meter should have the following features:
ANT+
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.
Zero offset
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.
Temperature drift
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.
Left/right balance
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.
