Under Pressure - Power Meter System Overview

They have been established in professional cycling for many years and are also indispensable in the ambitious environment of leisure cycling: power meters. The small measuring units provide precise and reproducible performance values of what a rider puts out. Cross-disciplinary. The basic principle of power measurement has been retained since the pioneering times at the beginning of the 1980s, when Ulli Schoberer developed the first power meter and later sold it with his company SRM. In recent years, however, more manufacturers have come into the market, which has led power meters to become significantly cheaper. And they supplement the heart rate monitor as a training control tool, if not even replace it. For some years now, not only professionals have been watt-controlled. No, more and more ambitious recreational cyclists rely on the numbers that the bike computer relentlessly and honestly displays in training and competition. 

The argument for measuring performance is obvious in ambitious cycling and competition: When I know what power I can push out and for how long, it opens up the space to better control performance and ultimately improve results. The more precisely you control the intensities in training and competition, the greater the training effect and an improvement in results. In contrast to the heart rate, which reacts quite sluggishly and time-delayed to load changes, power meters display the power with only a minimal time delay and basically "live". Especially on longer climbs a fast initial speed can be avoided. An experience that most of us have certainly painful had at some point.... Ergo: A power meter helps to keep output below the "threshold output" and to avoid "acidification".

Which power meter is preferred at the individual level in the end depends very much on two fundamental questions:

1. Should the power meter only be used on one bicycle or is it important for me to be able to quickly convert the device to another?
2. Do I need a power meter with bilateral measurement of the legs or is one-sided measurement sufficient (the determination of the total power is calculated in this case from the multiplication of the one-sided measured power)?.

One-sided or two-sided measurement?

A power meter that measures both legs individually naturally provides more accurate data, but a one-sided measurement is sufficient for performance-based training control.

Bilateral systems are particularly interesting when you know you have a significant imbalance between your two legs, or are returning from an injury that has weakened a leg more. In principle, however, it should be noted that for the athlete who only uses the power meter as a control instance for pacing, a one-sided system is sufficient. It is not for nothing that the athletes of Team Sky with the "Marginal Gains philosophy" have won several Grand Tours with one-sided systems from Stages.

The measurement on both sides makes sense especially for those who want to deal with the pedal stroke as a movement sequence in more detail. Here, in combination with the latest head units, bilateral systems simply offer more possibilities to analyse the motion and the efficiency of the cadence. However, you should make sure that it is actually a two-sided system: Spider-based power meters also only calculate the balance and do not measure individually. Here, one half of the pedal turn is attributed to the left leg and the other half to the right. Tension and compression phases can only be measured by pedal systems, the Shimano power meter, the Stages LR and the Rotor 2INPower, as these have separate strain gauges for each leg, including measuring and transmitting units.

Special cases

The following list shows the system differences and special cases related to compatibility with the bicycle to prevent a mistake when buying:

• Pedal power meters and power meters with measurement on the left crankarm are "no-brainers" with regard to the bottom bracket: You don't have to worry about it. The only thing to check is whether the new crankarm fits on the crank axle. Power meters, which come as a crankset with measurement on the spider, must be checked for compatibility with the installed bottom bracket. A glance at the manufacturer's information will help here.
•  With pedal systems, crankarm power meters and those power meters that come as cranksets with replaceable chainrings, existing chainrings can be ridden as long as the hole pattern matches. In all these cases the use of oval chainrings also works. However, when oval chainrings are used, Stages indicates a deviation in the measurement result and consequently a change in the FTP values.

In practice

When it comes to connectivity, the ANT+ standard is the first choice for power meters. Lately, Bluetooth LE has also become more widespread, which above all facilitates its use on a turbo trainer. (Most laptops do not have an ANT+ receiver and need to be equipped with a dongle to use Zwift, Rouvy and the like. Bluetooth is the connection standard here.) For bike computers, there are normally no standards that cannot be processed by a particular manufacturer.

Finally, it is certainly interesting to know whether one prefers a system with a permanently installed rechargeable battery or exchangeable rechargeable batteries: The advantage of rechargeable battery-powered devices (such as those from SRM or Favero) is that nothing can go wrong when changing batteries. However, I'm sure there are a few Garmin customers, on the other hand, who can probably sing a song about the precision need to replace the batteries.

However, if you forget to charge the power meter battery before the ride, then you will be standing at the start line without wattage values. Admittedly, this rarely happens with an SRM that has 3,000 to 4,000 hours of operating time, but it can happen more frequently with the Faveros. Here the batteries must be charged every 40 hours at the latest.

For systems with batteries, it is advisable to carry a corresponding battery in your bibs or jersey pocket, at least during training. Just in case. However, the nearest petrol station can usually help out too.