Power meters have become an essential tool for training and optimising the performance of professional cyclists and they are also now becoming popular among amateur cyclists. Here, we will look at the reasons for their success and the types of power meters available.
A power meter measures a cyclist’s power output, and this is calculated by measuring the force applied to the pedals and the angular velocity, or cadence, which is then recorded in watts (W)..
Force is usually calculated using a strain gauge, which varies in electrical resistance according to the pressure applied to the pedals. The angular velocity data is provided by a cadence sensor. Without going into complicated formulas and technical explanations, the important thing is that they allow you to record this power at a given moment and over a period of time, obtaining essential parameters for analysing your performance and planning your training sessions, such as maximum power, average power, watts/kilo, thresholds, work zones, etc.
The most important advantages of training with power data and the reason for its success, compared to the heart rate monitoring system are:
These advantages have led to power data becoming the basis for training control and planning, although heart rate continues to be an important factor for complementing information on your physical condition.
But, although few in number, power meters also have some drawbacks:
The different types of power meters depend on where they are located on the drivetrain. The location influences the data recorded, because it loses power, the further away it is from the pedals, which is where power transfer takes place. But, in general, quality brands have managed to make data very reliable and even comparable from one brand to another. The margin of error of the power meters we will be looking at is between 1% and 2% and cyclists give most importance to the constancy and reliability of their records, so that the references used to mark thresholds and training zones are valid.
The power meter sensors can be placed in the:
To choose the most suitable one for you, you will need to take various factors into account and we highlight the most important below:
Now we will look at the different types of power meters and their features, and the best-sellers.
We will not include systems that are limited to estimating power, using factors that are external to the drivetrain, such as those located on the handlebars or in electronic devices.
We will start with power meters housed in the
rear wheel hub, which is the furthest from the pedals.
Power Tap designed one of the best selling rear wheel hub power meters that lasted for years, before being overtaken by newer systems. It can be purchased either as a complete wheel or just as the hub for mounting on any type of rim with the same number of spokes.
Pros: easy to fit and swap the wheel from one bike to another.
Cons: This system can't measure both legs independently and if you change the wheel during a race and the replacement wheel doesn't have the gauge, you’re data will not be recorded. Prices are in the high range.
Power Tap G3 Brands, such as SRM, SRAM, FSA or Shimano opt for placing the power meter on the spider or chainring, in the case of the Power Tap C1.
The spider is one of the most reliable and accurate systems. It has become popular among professionals and is the favourite of big brands such as Specialized and Scott who install it in their top-of-the-range collection.
Pros: Reliability and precision. Measures both legs individually.
Cons: Little or no swapping between bikes, because this would involve removing the whole bottom bracket, so it has to stay on one bike. Prices are on the high end.
Sram Quarq DZero 
Similar to the spider measuring system, the crank arm power meter has the same level of precision and a similar price, but there are also more attractive options that are installed on a single crank and reduce the budget and weight considerably.
4iiii, is a top-selling brand that has made an important niche for those who
want a crank power meter using a very tight budget.
The design incorporates the power meter in the
left crank, and data is collected and estimates the total power output with surprising accuracy given its price.
Just
replace the original crank with the 4iiii, which is exactly the same, and set up the device. The left crank option is currently only available for best-selling road and MTB Shimano models. Other brands measure both cranks and even allow the possibility of inserting the power meter on your own crank, but prices are increasing.
Pros: Reasonably priced models start at 300€. Easy to fit. Excellent value for money. Very low weight at just 9g. for the 4iiii.
Cons:They only measure one leg. They are not compatible with all crank models.
4iiii left crank with power meter 
In this case, the power meter measure the torque inside the bottom bracket. The Spanish brand Rotor has gained a leading position in this type of power meter with the INpower, which measures on a single crank, and the 2INpower, which measures on both.
Pros: The components are hidden in the bottom bracket for better protection. Versions are available for almost all types of bottom brackets on the market. Lightweight. It records how your force is applied to the pedal during 360º crank rotation, providing important information on your pedalling performance, apart from all the power parameters, which you can analyse with the Rotor Power App.
Cons: Like the spider models, it can’t be swapped between bikes. It only measures one leg in the case of the Inpower and its price is at the high end, but it is high quality in terms of both technology and construction.
Rotor Inpower and Rotor 2INpower 
Increasingly popular as they are so easy to fit and there is a wide range of models available. The most widely used at present are the Power Tap P2, which measures both legs, the Garmin Vector 3 and 3S, the first measures both and the second, one leg, and the Favero Assioma UNO and DUO, as their names suggest, they measure one or two legs. The price range of these models is approx. from 400€ to 800€. In a higher price range are the Polar Keo Power and the Look SRM Exakt. But all these are only compatible with cleats and road shoes. This year, SRM introduced the first MTB pedal with power meter, called SRM X-Power, although they are not yet available.
Pros: Easy to fit, which just consists of screwing the pedals to the cranks, although some models require a torque spanner to apply an exact tightening torque to correctly register the force correctly. They are easily swapped between bikes. Low price, especially in models with a single pedal sensor.
Cons: They are more exposed and can suffer from impact and falls. They are not currently available for mountain cleats, which are also required for Gravel and Cyclocross.
Garmin Vector 3 and Vector 3S pedals 
Favero Assioma DUO and UNO pedals You can find more information in this video with an in-depth analysis of the Favero Assioma pedals.
We mention this type of power meter, located
in the sole of the shoe itself because
prototypes have emerged in recent years, but so far
none have been marketed and for this reason, we will not expand further.
Some models can be found with a
sensor in the cleats that is compatible with road pedals, but their presence is not yet significant in the sector.
and you will find the best advice and range of power meters at our Mammoth stores and at mammothbikes.com
See power meters at Mammoth
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