The bicycle power meter

There are various gadgets on the market for monitoring your cycling performance. Bike computers are particularly popular for targeted training. Modern devices not only measure speed, altitude or time. With the help of additional sensors, the cadence or heart rate, and thus the pulse, can also be determined. The data collected makes it easier to monitor and improve performance during training. Athletes often attach great importance to their pulse. However, heart rate in particular is strongly influenced by external factors. It is more effective to orientate oneself on the performance achieved. This can be measured with the help of a power meter. In road cycling, this tool has enjoyed great popularity for quite some time. Due to the precise measurement method and the good comparability with other road cyclists, professionals have long relied on this type of training control. A power meter can also be worthwhile on the MTB. Here are the most frequently asked questions about the power meter answered.

What is a power meter?

A powermeter is a power meter. It measures how many watts are generated while cycling. This happens in real time. The power generated while pedaling is the force applied while pedaling and the frequency at which pedaling occurs. Cadence means the revolutions of the pedals per minute. So the powermeter measures force and cadence, then a bike computer calculates the power. There are different types of powermeters that can be mounted on the road bike. Power measurement by a powermeter is particularly reliable because factors such as the incline or decline of the route and headwind are irrelevant for the measurement. Only the power that the rider brings to the pedals at what speed counts. The watt measurement is very accurate.

When is a power meter worthwhile?

Anyone who likes to collect data while cycling and also uses it to achieve training goals usually uses a bike computer for this purpose. Bike computers measure various values such as average speed, times, altitude and much more. Many devices can also be retrofitted with additional sensors that can determine the cadence or heart rate, for example.

Especially the heart rate should not be seen as a benchmark for monitoring the training. After all, our pulse is dependent on various external influences such as temperature conditions, or individual factors such as food intake or state of mind. For example, we are particularly nervous during a competition, which is visible in our heart rate. In addition, there is a temporal difference between the load and the pulse. Especially during interval training, it is noticeable that the pulse reaches its peak only after the high load. So the heart rate is not a reliable source of data to design your own training. Rather, it tells how the body reacts to load. Also, repeatedly reaching a certain average speed is not a mature training strategy. Likewise, speed is closely interwoven with other factors such as the incline, the gradient of the course or headwinds. How much power is actually produced is shown by the powermeter without any time offset. Idle times are also measured. If you stop pedaling downhill, there is no training effect. If you monitor your heart rate or average speed, however, this is not noticeable. The power meter, on the other hand, reveals the truth.

Riding can thus be controlled very precisely and objectively, whether during training or a competition. The additional measurement of the heart rate still makes sense for cyclists to get a feeling for how which training intensity feels. For example, during a triathlon, you can better rely on your body's feeling, and better allocate the available forces. This requires experience with the performance and the body feeling that prevails. In order to increase your own performance, it is therefore advisable to support the documentation of the data with a powermeter. Thanks to the ever-increasing mass of powermeters being purchased, they have been affordable for several years and are no longer reserved for professionals. A comparison with other road cyclists is also feasible based on the power. Comparison to one's own previous workouts should also not be underestimated. After all, a comparison of heart rate would always be very inaccurate due to the many determining factors.

A power meter also helps to find out what type of athlete you are. Some cyclists like sprints more, others are naturally more talented in long-distance riding. A powermeter doesn't just make sense for road cyclists. Interested mountain bikers can also measure their performance with it. This is especially worthwhile because of the often high number of meters of altitude climbed. Power meters can also be attached to a Gravel bike or E-bike . What's exciting about a powermeter is not just the power measurement to track a training goal. It can also provide new motivation while riding by competing against oneself. It is much more likely to go to one's limits than pure training by gut feeling. By the way, a power meter can also be useful on a roller trainer. Even when training indoors, you usually want to monitor your performance values. Especially the distance covered on the roller trainer can be better determined by a power meter.

How does a power meter work?

There are different types of power meters. The cadence can be measured either by a magnet on the pedal crank and a sensor on the chain stay or electronically by determining the length of the generated sine wave. The force is usually determined by so-called strain gauges. Strain gauges have an electrical resistance, when deformed it changes. The resistance changes depending on how strongly or weakly the pedaling is done while cycling. The power data is collected by the powermeter and then forwarded to the cycling computer. Here they are calculated and displayed digitally.

What does a power meter show?

A power meter can display power in several ways. First and foremost, the current power in watts can be displayed constantly updated. The power display is also possible in three, ten or 30 second intervals. Thus, it no longer fluctuates so extremely. The cadence must be determined by the power meter, since it is essential as a value for power determination. Pedaling time and pedaling index can also be derived from the cadence. The pedaling time is the total riding time minus the rolling phases in which no pedaling took place. The pedaling index represents the relationship between total riding time and rolling phases as a percentage. After a training session, the maximum power as well as the average power can also be retrieved. It is important for the average power to also include zero values. This can be selected in the menu. Especially on routes with frequent changes in altitude, otherwise only the power applied on the ascent would be taken into account, but not the idle power on the descent. Thus the average value can be falsified.

The so-called FTP value, also called functional threshold power value, means the highest power that can be maintained during a one-hour ride. This FTP value can be used to derive training zones. For example, in which area one actively regenerates during the ride, when the basic endurance is trained, where the lactate threshold lies or when one rides in the anaerobic range. This supports targeted training. After all, neither too strenuous nor too restful training is performance-enhancing. So if you follow a training plan, you get the relevant data for it. Efficient training can be achieved even with just a few hours a week on the bike. The so-called Training Stress Score is also referred to as training load on the Strava app. This refers to the rest period in which the body has to recover from the training. The measured heart rate and power are put in relation to the FTP value. The rest period is particularly important for achieving a training effect. During this time the muscles regenerate and build up. The racing bike power meter allows the performance of different athletes to be compared particularly well. This is due to the display of weight-related power, i.e. watts per kilogram.

With powermeters that measure on both sides, additional values can be measured. TE stands for torque efficiency. Positive and negative torque are included in the valuation. Each leg is calculated individually. The positive torque means the force that pushes the pedal down. The negative torque means the counterforce of the rear leg. The pedal smoothness indicates how smoothly the pedaling is. The balance shows separately how the distribution of the total power of both legs varies.

What power meters are available?

There are different types of powermeters on the market. Powermeters can measure on one or both sides. The one-sided measurement is usually measured on the left by a sensor on the pedal or crank arm. The bilateral measurement is done by two sensors that are independent of each other. A bilateral measurement is useful to identify which leg is more powerful. This imbalance can be attributed to various causes. Different length legs, differently developed muscles or a hip malposition are anatomically determined reasons. Exhaustion during cycling can also increase a dysbalance. A one-sided measurement often doubles the values to determine the other leg. This results in inaccurate power readings. Power meters with one-sided measurement are usually less expensive. Measurement errors and interference due to two sensors are also more likely with a two-sided measurement. The different types of power meters are presented below.

Powermeter pedals

Powermeter pedals are power meters on the pedal. The force exerted on the pedals when pedaling can be measured and calculated together with the cadence in power as watts. The installation is quite simple. Thus, the powermeter pedals can also be quickly exchanged between different bikes. Powermeter pedals usually fit modern cranks, so there should be no problems during installation. However, pedals are heavier due to this type of power meter. This is due to the strain gauges, which are necessary to determine the force, as well as the battery. Before buying such a pedal system, you should inform yourself as a driver of click shoes, however, whether the pedals are compatible with the cleats. Price-wise, power meter pedals with a sensor start at about 400€. For a double-sided measurement, the price can be twice as high.

Powermeter on the crank

Powermeters can measure the power on one or both crank arms. The power is also measured here via strain gauges. Power meters on the crank are very light. Since cycling is about every gram that can keep you from your best time, it makes this type of power meter particularly attractive. In addition, they are considered not particularly expensive compared to other power meters. Unfortunately, it happens that some power meters on the crank are incompatible with the frames of older bikes. So before buying should pay attention to this. With the one-sided variant of the power meter on the crank, it should be ensured that the crank arm fits the crankset. The crank arm thus needs the same length as the crank arm of the other side without Powermeter. For the double-sided variant, the crankset including powermeter must fit the bottom bracket of the bike. Per side, the price of the powermeter on the crank varies between about 200€ and 800€. Thus, they are usually somewhat cheaper than the powermeter pedals.

Spider-Powermeter

This type of power meter is probably the most commonly seen. The strain gauges that measure power are located in the crank spider. The crank spider is also called a spider. Spider power meters come in a variety of sizes and shapes. Thus, a model can be found for every bottom bracket and all chainrings. Professional athletes have long relied on this method of power measurement. This is due to the accuracy guaranteed by spider powermeters. In addition, they are considered to be particularly durable. However, spider powermeters are not as easy to change as, for example, powermeter pedals. Thus, they can also not necessarily be used on different bikes for training. This is also due to the limited compatibility of spider powermeters. They must be relatively precisely matched to your own bike . Before buying is therefore to pay special attention to whether the respective Spider-Powermeter also fit the crank and the bolt circle diameter. In terms of price, you can expect about 400 € to 600 €. Thus, Spider-Powermeter move in the midfield.

What do I need to consider when buying a powermeter?

Before buying a power meter, you should think about whether you prefer a one-sided or two-sided measurement. This has an impact on the measurement variant that one should look at devices. Also how much one is willing to pay can be considered in advance. The powermeter should also be compatible with your own bike computer. In cycling, every gram of weight counts to achieve best performance. Therefore, looking at the weight of the powermeter before buying is also important, so as not to be annoyed afterwards.

What are the popular power meter models?

As with all components and gadgets for the bike, particularly good products crystallize after some time on the market. There are also some manufacturers that stand for high quality. A few of them are mentioned below. However, there is no claim to completeness.

Powermeter pedals

Favero Electronics is an Italian manufacturer. It has the Assioma Uno or Assioma due power meter pedal on the market, which stands out especially due to its low weight. Assioma uno measures on one side, Assioma due on both sides. Garmin also offers good power meter pedals. The Garmin Rally as well as the Garmin Vector pedals are popular. Also Wahoo or Powertap build popular powermeter pedals. Wahoo offers models such as the Powrlink zero. In the vernacular rather unknown is the brand Look. The Look Keo pedals rely on SRM electronics and offer high quality.

Powermeter on the crank

Stages Cycling is an American company and is considered one of the most famous companies for the manufacture of crank systems. They are compatible with cranksets from the largest component manufacturers. Whether Shimano, Campagnolo, Sram or Cannondale. There are the power meters both one-sided and two-sided. The power meters from States Cycling have a long battery life. Other manufacturers for power meters on the crank are Shimano itself, but also 4iiii Innovations, Pioneer or Rotor. 4iiii offers, for example, the Precision Powermeter. The Sram dub series is also a well-known powermeter series for the crank. Power2max manufactures double-sided power meters for the crank. The Shimano dura-ace is probably one of the most common double-sided crank sets with powermeter. Also for the Shimano 105 or Shimano Ultegra there are crank arms including powermeter. The Sram rival axs can be supplemented by a suitable powermeter, as well as the Sram red. As a powermeter on the crank bidder Rotor the Rotor inpower or 2inpower.

Spider-Powermeter

SRM stands for Schoberer Rad Messtechnik. They mainly produce spider power meters. The SRM Origin is particularly interesting because it offers a lot of scope for your own configuration. Both spindle and crank and chainrings can be adapted to your own needs. Thus, the appropriate model can be selected for the own bicycle frame including bottom brackets. Rotor, FSA or Quarq also produce outstanding spider power meters. Not to be confused with SRM is the brand Sram. It also produces good spider power meters like the Sram AXS. The company Rotor, for example, has the INspider powermeter on the market.