For a long time, so-called power meters or watt meters were withheld from cycling professionals, which was due to the very high cost of the devices. They have now become more affordable, which is why ambitious amateur cyclists are also interested in the power meters. The purpose of the watt meter is to accurately record your training progress in order to be able to better control your own training.
A power meter or watt meter calculates how much power cyclists use when they pedal. To determine the cyclist’s performance, a power meter measures the material deformation in the pedal, crank arm or crank and relates it to the cadence. Accordingly, there are three different types of watt meters for racing bikes:
They all work essentially the same and simply differ in where exactly the material deformation is measured. Power meters then forward the determined data to an output device, such as a smartphone, via Bluetooth or other wireless data transmission.
Power meters measure data and forward it. That’s all well and good, of course, but it’s of no use if this data isn’t evaluated. A power meter only makes sense if you want to specifically control your training based on performance data.
There are several ways to train based on data. You can log the average speeds of your workouts. Or you can time yourself for the same distance or record your pulse with a heart rate sensor and draw conclusions about your training progress. So why the watt measurement?
Because the power meter data is independent of external factors. Your speed on the bike, for example, depends heavily on the tailwind or headwind, and our heart rate is also at least partially depressed or increased by parameters that we can hardly influence, such as the weather. In addition, heart rate monitors always react with a delay to changes in load. As a rule, after increasing the speed or climbing a mountain, it takes a few seconds until the higher pulse rate is displayed. A power meter is more responsive at this point and therefore better suited to controlling cycling training.
Ideally, you should combine your training data, measuring pulse, wattage, speed and depending on the data, for example to take your daily form into account during training.
Let’s start with the crank arm power meter because the pedal power meter is the easiest and cheapest entry into the world of watt meters for racing bikes. Simple because the installation is just as easy as with pedal systems and cheap because only one crank arm is required.
Crank arm systems usually only measure one side, i.e. only the pressure of one leg, which is then multiplied by a factor of two. Although a round and balanced pedaling of both legs is advisable when cycling, in reality it is hardly possible because most people’s legs have different strengths, which is why the measurement result of one-sided power meters is usually somewhat less precise than those of both sides.
The fluctuations mentioned between the right and left leg are between 4 and 6 percent for most people. For amateur athletes, the resulting measurement inaccuracies are bearable, especially when you consider that crank arm power meters are generally cheaper than pedal systems. Logical: Of course, before buying, pay attention to how long the right crank on the chainring is and buy the power meter for the other side in the same length.
A recommended entry-level watt meter for racing bikes is the Shimano 4iii Precision 3. According to the manufacturer, its button battery lasts 800 hours before it needs to be changed. In addition to the wattage from zero to 4,000 watts, the power meter also measures the cyclist’s cadence from 30 to 170 steps per minute. The 4iii Precision communicates with the bike computer or cell phone via Bluetooth. Compatible apps include Zwift, TrainerRoad and SYSTM, with which you can accurately log your training and evaluate it later.
With power meters in the pedal, you usually have to save the length of the crank arm once, because a longer crank arm results in a longer circumference that cyclists cover when pedaling. If you enter the wrong length there, the result will be incorrect. This step is not necessary for power meters that are located in the crank arm or on the chainring.
You should also pay attention to the screw-in depth of the pedal axle in pedal systems. Logically: the smaller it is, the smaller the material deformation and the longer it is, the greater the material deformation. Here too, it is important to pay close attention to the manufacturer’s instructions, otherwise the measurement results could be falsified.
In addition, the pedals are one of the most exposed components on the bike. An unfortunate fall and the expensive power meter is gone. Power meters on the chainring or in the crank arm are slightly more protected against accidents.
Pedal power meters offer a practical advantage over the one-sided crank arm: installation is even easier. This should be particularly interesting for owners of multiple bikes who don’t feel like buying multiple watt meters and who are interested in changing the power meters quickly. The pedals can be easily turned off and on again.
When it comes to measurement, most pedal systems also work on one side. The one-sided pedal power meters are priced at the same level as the crank arm systems. Double-sided pedal watt meters cost around 800 euros and more.
An example of a double-sided pedal power meter is the Garmin Rally, which is available in different versions:
It looks cryptic at first, but it’s simple. The 100 or 200 tell us whether the power meter is in one or two pedals. Logically: 100 stands for single and 200 for double. XC, RS and RK provide information about the click system of the pedals. The pedals for racing bikes and gravel or mountain bikes often differ in the click system.
Nice: Anyone who rides both a mountain bike and a racing bike will be happy to be able to fit the power meter in the different pedals because the measuring instrument is located in the pedal axle. And you can mount this pedal axle in the different Garmin pedals. The conversion takes between ten to 15 minutes and requires not only the right tools but also some manual skills.
Otherwise, the Garmin power meter works very well with the in-house bike computers. But collaboration with other bike computers is also possible. According to the manufacturer, the integrated battery lasts up to 120 hours, but it is definitely special. This is a CR1/3N or LR44/SR44. Here it is worth buying the batteries in advance.
Power meters located on the chainring typically measure the power of the left and right legs. However, installing them is very complicated because not every power meter can simply be screwed onto the old chainring, which is why you usually have to buy and install the chainring, crank arms and power meter from a manufacturer.
This also means removing the old crank axle, the crank arms and the chainring and then installing the new equipment with a power meter. This can be a difficult undertaking for beginners or inexperienced mechanics. And then the power meter is limited to one bike; quick changes like with the pedals are not possible.
The market leaders in chainring power meters are the watt meters from Quarq in conjunction with the chainrings from SRAM. The manufacturer’s models also include the Sram KRG Red AXS D1 Quarq Dub power meter, which is available in different versions in terms of crank arm length and chainring size.
With a price of 1120 euros, it is one of the most expensive power meters in comparison, which is also due to the fact that the package includes a crankset. If you know the right chainring and crank arms are installed on your bike, you can save money and buy the power meter separately.
Otherwise, the power meter measures the performance of both legs and works with many bike computers thanks to Bluetooth or ANT. If you already have a bike computer, you should of course check beforehand whether the power meter is compatible with it.
To recognize training progress, athletes like to use the so-called FTP value. This can be determined particularly well with power meters because their data is independent of external factors. FTP stands for “Functional Threshhold Power”, which literally means “functional threshold power”. This threshold power (FTP value) represents what power a cyclist can just maintain over a 60-minute time window.
At 100 percent of the FTP value, we can cycle for exactly one hour. Cycling becomes 80 percent of our FTP value, we can ride for longer. And if we drive above our limits (at 150 percent, for example), the speed can only be maintained for a short time. If we start our training with the power meter, it makes sense to first determine the FTP value, then train and repeat the same test again a month later. If the result improves, we can see relatively precisely by what percentage we have increased our performance.
Determining the FTP value is relatively easy in theory. Either you ride as fast as you can for 20 minutes, average the power meter reading and multiply the result by 0.95. Or you can simply cycle for 60 minutes at your maximum power and calculate the average from the power meter data. For both methods, consistent test routes or, ideally, a roller trainer are recommended so that you are not exposed to external factors such as traffic or weather conditions.
Sources: youtube.com/fahrrad-xxl.de youtube.com/enjoyyourbike youtube.com/ridemedia youtube.com/gcnaufdeutsch
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