Cycling Power Meters
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Cycling Power Meters – Overview and Styles
Power meters are to performance cycle training today what heartrate monitors were in the 1990′s. Simply put, if you are not using a power meter to train, and using it properly, you are not training to your potential. While a power meter that is not used properly can become little more than an expensive speedometer, a power meter that is used well can be an incredibly informative tool. A power meter is a tool that can elevate your riding and help you understand your metabolism and technique in ways that required a physiology lab in the past. A power meter is also like owning your very own wind tunnel as it can be used to analyze the aerodynamics of your equipment and position more effectively and realistically than an actual wind tunnel.
While a good coach is the best way to learn how to use a power meter effectively in your training, it is the job of a good shop to make sure you understand the technology that is currently available so that you can choose the system that is best suited to your needs. There are about a half dozen systems available that measure power when riding and they do it through a variety of methods. This part of our site is designed to provide an understanding of the different types of power meter systems and their corresponding benefits and considerations. The more informed you are with practical knowledge on the options, the better a decision you can make for your individual needs. Here is what you will find within:
Types of Power Metering Systems:
- Strain Gauge: Strain gauge based systems were the original method of measuring power and remain some of the most accurate meters today. Strain gauges are usually small metallic wire grids whose electrical resistance varies proportionate to the amount of resistance (strain) put against them. The number of strain gauges in combination with the materials, construction and alignment of the unit, determines how accurately a device reads. The pluses of these systems are that they can have a high degree of accuracy, can be some of the most reliable, and offer multiple locations of power measurement. The potential drawbacks are that strain gauges are not cheap and the electronics must be very well sealed to provide reliability. SRM and PowerTap are the two most common and proven strain gauge based systems and Quarq by SRAM has more recently demonstrated that strain gauge technology can work well in their design as well. Garmin’s Vector power meter remains unreleased. This pedal-based solution has potential though as it places small strain gauges in the pedal spindle, which not only addresses some of the limitations of other systems, but holds the potential to offer features not found on current systems and cut weight too. Stages Cycling StageONE power meter is a non-driveside crankarm based power meter that is one of the least expensive and lightest power meter options.
More information on Garmin Vector Power Meter
More information on Look Power Pedal Power Meters
More information on PowerTap Power Meters
More information on SRAM Quarq Power Meters
More information on SRM Power Meters
More information on Stages Cycling Power Meters
- Optical Sensor: Optical sensor based systems use wave sending sensors in combination with perforated discs to measure distortion in a known variable (like a bottom bracket axle). In the case of a power meter, the perforated discs can be attached to the bottom bracket shell and the sensors can be attached to the bottom bracket spindle. When load is placed on the axle through pedaling the sensors twist and distort in relation to the perforated disc and the distortion is measured and converted to watts for the rider. Optical sensors have little to no mechanical wear and thus should be reliable and consistent once installed. Ergomo was the primary optical sensor based system, but distribution and fabrication issues plagued the idea and Ergomo has left the U.S. market. Optical sensors remain a very good idea, but one that has not been executed to its potential.
- Vibration Monitoring: Vibration monitoring systems convert vibration into wattage through sensors and calculations based on variables like speed. Polar’s system uses vibration monitoring and the system consists of a magnetized sensor that mounts to the chainstay. This sensor detects vibrational changes in chain tension and combines this information with some measured variables on the bike to calculate power. The benefit of this type of system is that it is inexpensive and it will work with some existing Polar units. However, it needs to be considered that the system is not as accurate as some of the other methods and mechanically it can be challenging.
- Equation Based: Equation based systems calculate wattage by monitoring a variety of contributing forces and then using good old physics to calculate the end result. For example, by combining all the forces that a cyclist must overcome (wind, rolling resistance, gravity, inertia…) and combining this information with the rider’s speed and other environmental factors, wattage can be determined. The more accurately all the different variables are being monitored, the more accurate the end result. By creating a unit that adds in the variables that are not (wind, for example) currently being monitored with current technology, you can have a power meter that weighs about the same as a cycling computer and does not require any mechanical hardware outside of what a cycling computer usually consists of; this means a simple and inexpensive system. The potential drawbacks are that some of these variables can be difficult to monitor consistently (like wind…) and accuracy can be compromised if the input information is compromised. iBike and CicloSport use an equation based system. We do not carry or recommend the CicloSport because of chronic quality problems.
Explanations of Important Variables to Consider:
Accuracy: For the purposes of cycling power meters, we refer to accuracy as the consistency of a unit on a day-to-day basis. Are the results from a week ago comparable and relative to the results from today? A power meter’s primary function is to provide functional information and thus accuracy/consistency is the most important function and the one we weight the heaviest. Effective training requires that the results be consistent session to session and this category looks specifically at how little variance the meter allows.
Reliability/Maintenance: The highest tech piece of equipment in the world is pretty worthless if it does not work as designed half the time. How reliable the unit is and how often it needs servicing is part of what to consider while how much regular data input and consumables (batteries, for example) are required is another. Finally, how responsive, supportive and stable the company behind the product has been is of significant value.
Compatibility/Limitations: Outside of price, compatibility and limitations of a power meter’s design are the biggest variables that determine which power meter makes the most sense for you. Compatibility and limitations refers to whether there are any issues using the unit with certain frames or components and the ease of use on multiple bikes. We list some of the most common limitations to be aware of in each product’s page. For many riders, this is one of the more important areas to understand as each unit has its benefits and compromises.
Display Quality and Features: This used to be a very important set of variables when selecting a new power meter as the power meter would often only work with one computer – the one that was made by the same company. However, now that many power meters are ANT+ compatible and you can use computer displays from aftermarket manufacturers like Garmin, the computer head you select and the power meter you use can often be independent decisions and this is great news for power meter users. Things to keep in mind when selecting a display include how easy is to get where you want in the display, how much control you have over what is being displayed, how big and clear is the view, how many screens are available in the display, whether you have GPS functions and how adjustable the data recording options are. Displays have come so far in the past few years that even $250 displays like the entry level Garmin 500 now offer incredible control over the options. We suggest that you choose the ANT+ power meter you want first and then choose the computer head that provides you with the display and functionality you want separate as you no longer need to be restricted by brands or models as any ANT+ [power meter will work with any ANT+ computer head.
Weight: Power meters usually add some weight, so it is worth knowing how much and where the weight will be added.
Installation: Some units are almost as easy to install as a standard cycling computer while others require replacing drivetrain parts. Either way, all the wireless units have become significantly easier to install and than ever before.
Software/Hardware: While the download software you use is very important to your end satisfaction with the units, it is important to note that there is aftermarket software available that is frequently better than what comes with any of the units – CyclingPeaks software is a good example. Also, ANT+ has allowed many different computer heads and download options to be compatible with each unit, so many of the differences in computer heads from the manufacturer are not as important as they used to be as you can use any head unit you would like from brands like Garmin or PowerTap. Some brands, like Quarq, do not even make their own computer head and you choose an aftermarket computer of your choice. For these reasons, we don’t spend as much time discussing this category as we used to and we often recommend choosing a ANT+ compatible unit and then selecting a separate computer head (or heads) that suit your needs well.