Do power meters work? Is your power data real?

Power meters have undoubtedly changed the cycling landscape, from how riders train to how they decide on race tactics. (We’ve also seen average power from riders in races, and it’s amazing!) For more casual or online riders, the popularity of power meters has opened up another quantifiable metric. However, there’s an obvious problem when using a power meter for training – power data can be wildly inaccurate. In this case, is your power data reliable?

What is “real power”?

“Real power” is power output calculated based on energy expenditure. As riders, the unit of power we care about is WATT. WATT is a measure of work or energy done over some time.
On a bike, power is calculated by multiplying the force applied to the pedals by the angular velocity of the crank. In simple terms, power is how hard you’re pedaling multiplied by your cadence.

In reality, accurately measuring a rider’s power output on a bike is more complicated than it seems, and many variables affect the final reading. Everything from where you measure power to the equipment you use and the environmental conditions you ride in can affect the final power reading. From a power meter perspective alone, there are differences in the strain gauges inside a power meter and the software that manufacturers use to calculate power readings, which ultimately affects the accuracy of a power meter in terms of "true power."

Consistency is more important than accuracy

When it comes to the reliability of training data, consistency is far more important than accuracy. If you're using a power meter as a training tool for yourself, rather than a comparison tool, then the actual power number it calculates is largely irrelevant. What's more important is that the power meter provides consistent data measurements of the same output day after day.

The problem arises when you want to compare data between multiple power meters. This is a common situation many riders encounter when riding outdoors and using a trainer. If you feel that there is a large difference in power readings between the power meter on your bike and the trainer, running both devices simultaneously while training indoors can quickly confirm or eliminate your suspicions.

Weather can have a significant impact on some power meters

Some power meters are equipped with active temperature compensation (ATC), which is designed to improve the accuracy of the power meter while riding. Because power meters rely on strain gauges to measure small deformations in materials, temperature changes can cause the strain gauges or the materials they are mounted on to expand or contract. If temperature changes are not accounted for during a ride, the accuracy of the power meter can deviate significantly from its nominal range.
If you are using a power meter that does not have active temperature compensation, it will take some work on your part to keep the data relatively accurate. In addition to performing a zero calibration at the start of a ride, you will also need to perform a zero calibration mid-ride when the temperature changes to ensure accurate data.

Where the power is measured

Another factor that affects the accuracy of a power meter is where the power is measured. The easiest place on a bike to consistently measure power is the rear hub, which is the least forceful and most stable measurement location. Although hub-based power meters were once very popular, they have become rarer in recent years, with crank and pedal power meters being more popular.

Crank or chainring-type power meters are the more accurate and stable form of power meter and are generally used more widely. This is because they are subject to fewer random forces and are less susceptible to knocks, damage, and wear. Generally speaking, factory-installed power meters are more accurate than those that are upgraded from stock cranks.

The pedals are arguably the most difficult place to accurately and consistently measure power, partly due to their location, the size of the pedals, and the irregular forces that pass through them. The main advantage of power pedals is that they are easy to switch between multiple bikes, making them ideal for riders with multiple bikes.

The location of the power measurement can significantly affect the final power reading.

 

Unilateral or bilateral

This is perhaps the most obvious area where data can be erroneous. Compared to bilateral or total system power meters that measure a rider’s total output, unilateral power meters always leave some margin for error. No rider has perfect 50/50 symmetry, and while some riders have smaller differences between the left and right legs, all riders will have some inconsistency between the left and right legs. At low intensities, this difference is almost negligible, but as a rider approaches maximum power output, any difference becomes more significant. This means that for riders who are looking to accurately measure short bursts of power, a unilateral power meter may significantly underestimate or overestimate “true” power.

For this reason, unilateral power meters are best used as an introductory tool for power training, or for more general data collection rather than specific training. Muscle imbalances can also change over time, meaning the percentage difference for each leg will also change, making manual compensation less accurate.

Is power a reliable metric?

Power can be a very reliable metric, but it is not infallible. If you are looking for an absolute training metric, power meters may still be a little lacking. Heart rate data is still very valuable in this era. We are affected by factors such as sleep quality, nutrition, stress, and training load. All of these and many other factors will affect the rider's ability to output power on the bike every day. At this time, we need the reference of heart rate data. Combining power and heart rate for training is the best way.

 

Tags: #Superteamwheels #carbon wheels #powercalculation