Power meters: An Overview
Full disclosure – I’m sponsored by Rotor who make crank-based power meters for road and track. If you want 30% off their power products and 40% off their standard products send me a message, but you should read this article with that knowledge in mind.
What is a power meter? A power meter represents the gold standard of cycling data collection. It’s the most reliable way of telling exactly how much effort you’re putting into your cycling. They measure how hard you’re pushing on the pedals (force) and how quickly you’re applying that force (velocity). The result is power – something you can use to inform your training and racing to a degree of accuracy unattainable with other methods. You can then use this data to build really accurate and specific training plans, but that’s a topic for another day.
Before I talk about power meters in detail, I’ll mention some other methods of data collection and their drawbacks.
Heart rate lags power output by at least a minute, making it unreliable for many interval sessions. It’s also affected by stress, hydration levels, sleep levels, temperature, overall level of recovery and various other factors.
Speed is affected by altitude, air pressure, air temperature, clothing, tire pressure, humidity, body position, equipment choice and weather conditions.
Cadence is affected by fatigue levels, gear choice, riding in or out of the saddle and equipment restrictions and doesn’t necessarily tell you very much anyway.
It’s not that it makes no sense to measure these things because it does, but in an ideal world their place is to give context to the data we can get from more reliable sources – power meters or laboratory testing. Think of data collection like a meal; power is the main course and everything else is a side dish. You can certainly get by with sides, but you wouldn’t choose to if you could avoid it.
Types of power meter
There are four main types of power meter:
Crank-based systems
Pedal-based systems
Hub-based systems
Aerodynamic inference systems
Crank-based systems are (generally speaking) the most reliable, accurate, and expensive systems available. Single-sided power cranks measure one leg’s power output and double it to find overall power. This is very rarely as accurate as a double-sided system as almost all riders have some leg strength discrepancy at least some of the time, but it provides a solid baseline for a considerably cheaper price. Double-sided power cranks measure each leg’s output individually and combine the results.
The downsides of crank-based systems are the price (typically over £1k for a double-sided system) and the fact that it’s quite fiddly to switch them between bikes if it’s possible at all. In return, you get good battery life, very high accuracy, good reliability and little chance of accidental damage.
Pedal-based systems are the most versatile type of power meter. Again, they usually come in single or double-sided versions, with some manufacturers offering the ability to buy a single power pedal then upgrade to a double system down the line. The advantages are that you only need one power meter for multiple bikes, they’re easy to fit and they provide a high degree of accuracy. You can also replace pedal bodies as they wear out.
The disadvantages are that they have less battery life, are more susceptible to reliability issues (as you would expect, considering the pedals have to communicate with each other as well as a head unit), are easier to damage and can lock you into one pedal/cleat system. Early pedal-based systems were notorious for issues with data dropouts, and some had very specific and awkward fitting requirements. Newer systems have greatly improved on these problems and are far more reliable and user friendly, but beware of ebay purchases which may be of the previous generation.
Hub-based systems were popular in the early-to-mid 2010s but have largely fallen out of fashion with the rise of more affordable crank systems and more reliable pedal systems. Power was measured using electronics in the hub of the rear wheel. This meant that power measured by these systems would typically be a few watts lower than that measured by pedals or cranks because of drivetrain inefficiencies and that you didn’t have the ability to see data from each leg separately. The advantage was that you could use whatever pedals and cranks you wanted and pay a relatively low price for power data.
Unfortunately, you were tied into using the same rear wheel all the time if you wanted to keep your power data. While this was fine for training, it was less ideal for racing. Some riders solved this issue by using wheel covers or having power meters built into fairly nice wheels to start with, but it was always a consideration.
Aerodynamic-inference systems didn’t measure power directly at all. Instead they took the form of units that would bolt to your bars and measure environmental data – wind speed, temperature, pressure, bike speed etc. and estimate your power from there. Some people found them very accurate but most didn’t and they never really took off. They were much cheaper than other alternatives, but there’s no point in buying something cheap if it can’t do what it’s meant to do.
Hopefully that gives you an insight into the different systems out there along with some of their positives and negatives – ask if you have any questions!
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