A short guide to Power Meters

Whether you want to accurately measure your effort during short intervals or gauge the energy cost of a Ride , competition, or demanding event, the Power Meter an invaluable tool.

Its calculation of energy expended, in watts, is an objective measurement that does not take into account your heart rate or how you feel. Unless it is poorly calibrated or poorly designed, it does not lie: 200 watts is 200 watts.

But Power Meters all Power Meters are created equal. Some are more accurate than others. Others have one or more sources for data collection. Finally, depending on where the sampling occurs (at the pedal, Crankset, hub, etc.), there may be a disparity in the results due to the loss of power that results from friction between the source (your foot) and the measurement point.

To measure the force exerted by a cyclist, Power Meters in the same way, using an analog mechanism at various points in a power production chain that begins in your legs and ends at the point of contact between the tire and the surface you are riding on.

There are several types, which collect data from the pedals, cranks, Crankset axle, chainrings, or rear wheel hub.

Inside these components, mechanical power is measured using strain gauges that deform according to the force applied. The calculation is then performed using a fairly simple formula, by multiplying this torque, in newton meters (or N.m), by the angular velocity, or cadence, if you prefer.

Power (in watts) = N.m x angular velocity

This data is then transmitted wirelessly via ANT+ or Bluetooth systems to an electronic device that delivers the results in real time. This could be your small Garmin, Wahoo, Polar, or other GPS computer. Your phone, tablet, or computer.

Power Meters all Power Meters are Power Meters equal. First, measurement accuracy varies from one company to another. Some companies also offer Socks products Socks that are not worth Socks . But cost does not necessarily guarantee the best quality either. It is therefore best to check out forums and, better yet, consult our team before purchasing one.

We know them well: we have tested and compared almost all of them.

Most have a slight margin of error, between 1 and 2%. That said, it is important to always use the same sensor in order to obtain consistent results, because they are measured under the same conditions, according to the same standard. Beyond the margin of error, there are also differences in results depending on the type of device and where the measurement is taken. For example, between a pedal and a Crankset axle, the loss can vary depending on the flex of the Crankset arm.

A properly cleaned and lubricated chain causes a power loss of around 3%. But the same dirty chain can cause up to 10% of watts to be lost. Or rather, consumed by dirt, since the additional friction reduces the efficiency of the transmission mechanism.

The moral of the story: if you have a rear Power Meter , make sure you keep your chain clean.

Another thing: some Power Meters sensitive to temperature. Check if this is the case. If so, you will need to recalibrate before rides or colder than usual.

Otherwise, there are more and more versions with two cranks that allow you to make more accurate calculations, but also to correct the quality of your pedaling depending on the type of analysis software used.

If you use the wheels we rent at Cartel, you are familiar with this type of sensor. It is one of the oldest and most reliable systems on the market due to the simplicity of its mechanism. Don't be surprised, however, if you notice a noticeable difference between the figures obtained with this product and one of the other systems, since, as explained earlier in the text, there is a loss of power between the force applied and the force that remains after being altered by the various friction points in the drive system (chainrings, chain, sprockets).

Important note: since these hubs are often heavier than other systems and cannot be used continuously if the wheels are changed, they are gradually disappearing.

Still undecided? Write to us or ask our staff for advice. Maybe you only need a sensor for indoor training. Or perhaps you travel a lot and want to rent bikes while continuing to measure your performance. We can compare the costs, benefits, and effectiveness of different models with you.