10 Things You Didn’t Know About Power Meters

Jan Poshenko
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There's A Steep Learning Curve

No matter how many reviews I write and no matter how many power meters I own and test, there is still a steep learning curve facing riders who are planning to start using a power meter. The reason being that there are more power meters on the market than ever, and each design has its own specialities and peculiarities that impact where, how, when and why you should use it.

What follows is a quick run-through of my top 10 things you’d only know if you’re using a power meter. That will give you some perspective and inform you about things that can make the purchase decision easier.

Your pre-conceived notions can hold you back.

We all have those moments where we think, “this is what power is,” or “power meters aren’t that great.” Well, you’ve probably heard about the heartbreak that can happen if you think a power meter is going to singlehandedly transform your cycling … and it doesn’t. More often than not, the problems are caused by attitude, not the power meter. This goes for both bike and wheels.

You can have power for free.

You Might Turn into A Data Geek

We actually laughed when we came across a headline that read, “I’ve turned into a data geek thanks to my power meter!” By now, DAHON USA has sold enough power meters to employers and employees to begin to see patterns that we’ll share with you. But this rider isn’t alone. There is nothing more satisfying than watching a rider finally understand how to read their own power data. The moment the light bulb goes on and they see that their power data is open to whatever interpretation they can muster AND that such interpretation is wrong …

Power Meters Measure How Much Power Rider Produces

The first thing to know is that a power meter measures how much power the rider is producing. In real-world terms, this means exactly what you think it means. If you produce 100 watts and your friend produces 150 watts, you should be able to ride faster, longer, and healthier than your friend. Note: You don’t have to know what a watt is to make the above statement 100% accurate.

You Are Your Instrument – You Can’t Cheat

Power Readings can be Erratic

One of the most important things to understand about a power meter is that when you take a reading, you will not always get exactly the same numbers. This is because a bike computer doesn’t have the incredible accuracy of an electronic measuring device.

All of them rely on a tiny motor which sets off as soon as you press the button to measure your power.

This movement causes vibration within the device that can throw off the reading by a few watts.

Power Meters will Never Agree with Each Other

A Power Meter supplier could have five different models, and they will never get the same readings.

A Power Meter supplier could have five different models, and they will never get the same readings.

In a recent round of power meter testing in Cycling Weekly magazine, the numbers varied by as much as 20w on some of the readings.

In a recent round of power meter testing in Cycling Weekly magazine, the numbers varied by as much as 20w on some of the readings.

How do we know this?

How do we know this?

As part of the same test, we took the number of watts each meter read (n=5) and calculated the mean of each meter. Then we created a standard deviation for each, for example the SRM was 20w and the ROTOR was only 4.6w.

As part of the same test, we took the number of watts each meter read (n=5) and calculated the mean of each meter. Then we created a standard deviation for each, for example the SRM was 20w and the ROTOR was only 4.6w.

From there we calculated the +/- of each SD and as you can see in the picture below, the ROTOR was only 4.6w, whereas the SRM was a whopping 20w.

Power Meters are not 100% Accurate

If you have ever used a power meter, you already know that they are great for measuring your power output (and expenditure). However, they are not 100% accurate.

The most accurate power meters out there can be off by up to 1.5%, which is almost 20-30 watts in power output. This may not seem like a lot, but it can make the difference between dominating your favorite climbs and barely eking out a safe descent.

So if the power numbers seem all over the place, understand that you’re not crazy and that this level of accuracy is about as good as you can get with power meters.

Zero Offset

It is very rare in cycling that a power meter will be dead on at zero, so most people will be needing to compensate for the offset. You can do this by going into your head unit, and pressing the ignore zero button. Now the head unit will base the display, calculations, and reporting off of the average power for the ride, not the zero line.

If you know you are going to be testing many different power meters on a particular ride, it is best to just go ahead and press this button before you start the route. This will eliminate the need to hit the button each time, and you can just let it work in the background. Note that some head units will show an asterisk next to the average at the end of the ride.

But if you only press the button at the beginning of the ride, then the head unit will only use the average of your previous ride to measure from.

Power Meters are Susceptible to Temperature Changes

Voltmeters, ammeters, ohmmeters, and even wattmeters are essentially the same device, but use different means to measure different voltages, currents, resistances, and powers. When they were first being developed, many power meters were mechanical devices that relied on a spring balance or a pendulum to calculate the amount of movement. These moved directly with greater movement, which caused them to over-read.

Later models used a series of gears to divide the movement so that the instrument could read lower ranges, but were less accurate with larger movements. Most of these devices were also built to be very small and lightweight to reduce the impact that ambient temperature would have on the calculations. Electric motors were not yet common in the late 19th and early 20th centuries, so they were not designed to accept them.

These days, most common power meters are different types of semiconductor devices. Most of these are based on an RF bridge. These devices rely on an internal oscillator that is calibrated to a single frequency. When used a power meter, the power source is connected to the primary, which will send out pulses of RF at a single frequency.

Crank Arm Compatibility

A common mistake in selecting a power meter device is to focus on which crank arm type you want and then just choosing the bike that’s compatible with your favorite crank arm type. Although this is not necessarily a big mistake, it is important to know that there is a bit more to it.

Most power meters are designed with a few different crank arm types in mind.

Generally, these are compatible with both Shimano and SRAM cranks. It is true that some devices may not work with all crank arm types, but it is rare. This means that you can focus more on which device is right for you and then worry about the compatibility.

The cranks that power meter devices are compatible with vary depending on the manufacturer and model.

These may include the following:

A: Shimano Dura Ace (9000 series), Dura Ace 9000 left, Ultegra 6870 (6800 series) and Ultegra R8000 (8070 series)

B: Shimano 105 5800 series, Dura Ace 7800 series, Ultegra 6800 series and Ultegra R80 series

C: Shimano Tiagra 4700 series, Dura Ace 7700/7800 series, Ultegra 6500 series, Ultegra 6600 series and Ultegra R700 series

There's A Built in Cadence Sensor

Many power meters come with a built in cadence sensor. What some consumers don’t know is that this is only for the first few months of use while the unit is breaking in.

Cadence sensors are generally not used for longer duration sessions because they are not as accurate, although they may be included for those doing spinning classes and/or those that are simply looking to occasionally track cadence.

Cadence is more difficult to estimate when using a power meter than simply counting your steps, so one downside of including cadence in general is that power readings may be skewed.

First generation power meters only provide cadence readouts, so if your power meter has a cadence feature, then you’re getting more advanced technology. If your power meter doesn’t have the feature, then don’t worry about not having a cadence monitor and you can go ahead and get started with training right away.

Some power meters will move the cadence calculation to the head unit, which will be quicker than the more complex calculation done by the power meter.

Maintenance

The use of ultraviolet lamp and activated carbon filter for water purification equipment maintenance.

If we often use the UV lamp at home, how do we maintain it?

UV lamp is a long-term maintenance item, and we must carry out regular maintenance. At the same time, we must also maintain an orderly process of use, storage and cleaning. Otherwise, if the UV lamp is not in the correct state, it will affect the quality and stability of the drinking water.

{1}. The filter must be cleaned every two to three days when the water purifier is in use.
{2}. The ultraviolet lamp should be regularly checked and replaced when the average lamp life reaches 2000 hours.
{3}. How to clean the activated carbon filter?

In order to ensure that the filter cake does not become too thick, we should clean the activated carbon filter once every two to three days. At the same time, we should also clean it with water at a certain time.

Cleaning the filter cake regularly can ensure that the water purifier's filtration capacity and pressure are kept at an appropriate level. At the same time, it can also prevent the activated carbon filter from being blocked, resulting in replacement failure.

Summing Things Up

Now that you've read all about power meters, you're probably wondering why you didn't know about these incredible tools long ago. It's amazing how effective, accurate, and easy to use a power meter is, but because they're not that widely used, most people never really got a chance to see how great they are.

There isn't much of a downside to power meters. They're great because they measure exactly how much you're exerting when you're cycling, essentially letting you work out as efficiently as possible. They're going to make you faster and more efficient, and they're also going to bring some convenience to your training and help you achieve your workout goals.

There are a lot of different types of power meters, but most of them are pretty similar, and it should be easy to find one that works well for you. As long as you have a power meter, you can start looking forward to making major progress with your cycling.