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Antes de comenzar a publicar las diferentes pruebas de medidores de potencia (que llevo preparando ya durante unas semanas), creo que lo más oportuno es establecer un punto de inicio, y comenzar a desarrollar todos los detalles a partir de aquí. Algo así como una base de conocimientos a la que poder remitiros si en algún momento hay alguna duda «de base», algo que no sea específico de un medidor de potencia (o potenciómetro, como prefieras llamarlo).
What it is and what it's for.
Instead of measuring variables of the athlete or the bicycle that can be altered by external elements (heart rate, cadence, speed) a potentiometer measures the power developed by the cyclist. Technically the system is very simple (and economical), as you simply place a strain gauge somewhere on the bicycle that will measure the force applied when pedaling (and only when pedaling, so the other variables do not influence the measurement at all).
This force measured by the gauge, combined with the angular speed (in this case the pedalling cadence), is what allows us to obtain the absolute power. And therefore, only when pedalling, so standing on the pedal or pressing hard will not introduce reading errors, as there is no turning. This power reading allows us to obtain an objective measure of the real performance during training, which will also allow us to compare in different activities that you will carry out in the future.
Because 300W of power is the same regardless of the circumstances. Whether it is cold or hot, whether you are training in a gale or a leaf is not moving, whether it is raining or you are tired. And from a power threshold figure (FTP) it is possible to calculate the different intensity zones on which to prepare our training sessions, depending on the objectives pursued at each moment of the season.
In addition, power measurement is instantaneous, so if you are doing interval work the response is immediate. It is an accurate way to train with respect to a given target, especially when comparing it with other variables such as heart rate (which is much slower to climb and depends on many other variables) or speed (which depends on upwind or downwind or the slope in question).
Past the power meters.
Power measurement in cycling has not always been as important as it is today, where there is no professional team that does not base its training and racing on the power data of each of its riders.
But don't think that this is something new, the history of this type of device goes back many years, when shoulder pads, cassette tapes and the Sony Walkman were a trend. It is possible that the youngest people don't remember this (I don't want to give them to my grandfather, either), but those of you who already have a few springs on you will realize that we are talking about many years ago.
The first development dates back to the late 1980s, when Ulrich Schoberer founded the SRM company, which was the first to design a method for measuring power that a cyclist was able to develop. Until then, cyclists could only find out their power data on an ergometer in the laboratory. They had no possibility of training with this data as a reference, it was simply used throughout the season to check how they were doing.
This invention would totally revolutionise the world of professional cycling, in which all riders now base their training on power data - and not just training, but also in competition, especially in stages against the clock.
Pero si en el ciclismo en ruta profesional es una herramienta importante, es en el triatlón de media y larga distancia donde el uso de los potenciómetros se ha convertido en imprescindible ya que los datos que aporta son los que marcan el ritmo de carrera en el segmento de ciclismo. Incluso algunos van más allá y consideran el uso de un medidor de potencia como «trampa».
From the expensive old potentiometers to the new, much cheaper, wireless devices, development has not stopped since.
Today more and more brands are launching their own power meter. The measuring points are very diverse, from the rear hub to indirect measurement through air speed, to measurement in the shoes themselves.
If you remember, a while ago I indicated that at the component level it is a very economical system. And that's right, the cost in materials is very low. So why are power meters currently so expensive?
Even if the cost of the material is low, the entire product budget is in the development of the measurement method, that is, in the mathematical formula that translates the force exerted on the gauge and the pedaling cadence into watts. Because, as is logical, there is no point in having a power data if it is not reliable.
And yes, developing pedals or a hub with a gauge and an accelerometer is very simple, but adjusting the calculation algorithm so that the measurement is consistent when the force is high, when you're just exerting force, when the temperature drops dramatically (the elasticity of the materials changes enormously), when you're driving over very bumpy terrain (a torment for accelerometers), etc; that's where the complications, the difficulties for the engineers and the years of development are. In short, that's where the euros are.
Cualquier empresa puede fabricar un componente de bicicleta que mida la potencia de forma «casi correcta», pero desarrollar un sistema fiable en multitud de circunstancias no está al alcance de todo el mundo . Hacen falta conocimientos en muchos campos: elasticidad del material y los cambios según la temperatura, diferente elasticidad dependiendo de la longitud de biela, etc.
And when there are cyclists who can spend an entire season looking to upload their FTP in 10W, we are not talking about something trivial. It is not good to measure by eye, the data obtained must be totally accurate.
Types of power meters
There are many places where it is possible to measure power. Normally the location will determine whether it measures a little more or a little less, it all depends on where in the transmission the data is taken. As it is logical all transmission has a friction and this friction causes a loss of watts. This is always the case when we are referring to direct measurement systems (I will leave for the end the possibilities of indirect measurement).
To start with one of the corners of the transmission chain, I'll start with the solution presented by Brim Brothers a couple of years ago, but which so far has not has begun marketing through the Kickstarter platformThis power meter is unique in its kind. It consists of a sensor that is placed under the shoe, between the sole of the shoe and the cleat of the pedal (compatible with Speedplay pedals). It is connected by a strip to a transmitter that would be placed on top of the shoe. There are two options, only left side (doubling the power) or on both sides, which would allow to measure the total power more reliably.
The advantage it has is that it is totally portable and if you have several bikes you can use it on any of them indistinctly, as long as you use Speedplay pedals on all of them.
Similar in concept, but in this case the electronics are integrated into the pedal or an adjacent module. Many manufacturers have chosen this solution, which is usually easy to install. Its main advantage is that it is completely universal and does not depend on any other component of the bicycle, as the thread from the crank to the pedal is standard.
We continue to advance in the transmission chain and the next thing we find is the cranks. But we are already beginning to find compatibility problems. Specific models depending on the model of crank you ride, or the bike's bottom bracket, the type of chainrings (round or oval), etc. It's already more swampy terrain and we have to start to make calculations with compatibility.
The main exponent is StagesUntil now, the problem was that it was only compatible with aluminium cranks, but recently they have started to work with carbon fibre cranks as well.
Básicamente cogen una biela estándar y le añaden un «pod» donde se incluye la galga y la electrónica que envía los datos a tu dispositivo. Similar a lo que ofrece 4iiii Precisiononly in this case you're the one who would send your crank to put the unit in it.
In both cases you would only measure the power in your left leg and multiply it by two, which is its most important disadvantage. If your pedaling balance is not always stable (it usually varies with fatigue) the data will not be as accurate as we would like.
Spider and dishes
This is perhaps where we find the most options, but the compatibility problems continue, so you should look for an option that is compatible with your bottom bracket.
One of the latest additions has been the Powertap C1 chainrings. But there are many other options, mainly from SRM (if you have a VERY generous budget), Quark, Power2max, Pioneer, Rotor... Depending on the model, it will be a single leg or total power, being one of the most solid options.
We continue to move forward and we find the bottom bracket, that is, INSIDE the bottom bracket. Rotor integrates its power meter in this area, which keeps it totally safe from shocks, water and other problems that external units may suffer. There are other proposals, such as Ashton Instruments or Dyno Velobut they haven't been released yet.
And finally we come to the end of the chain, the rear wheel hub. Here there is only the presence of Powertap, which has been developing hubs with power measurement for many years. In fact in 2005 they launched the first wireless power meter (that's right, they used to have cables). Currently their best-selling model is the Powertap G3, although there are other versions with ceramic bearings or with bodies manufactured by DT Swiss.
Its main advantage is the simplicity to move it between bikes, as it is mounted on one wheel. But it is that same advantage that becomes its main problem, and that is that if you have several wheels (for training and for competition) you will have to choose on which one to mount the hub.
Finally we have the indirect measurement of power. And by indirect I mean it uses calculation algorithms from other variables, and it's not a direct measurement of force. First you have the PowerCal by PowertapIt is a simple heart rate sensor that also doubles as a power meter. Obviously, do not expect to have accurate data, but as a first approach to power training can be interesting for less demanding users.
By raising the budget a little you can also find the PowerpodIt is slightly more precise than the Powercal and bases its measurement on wind speed, inclination and its internal accelerometer.
Future. What do we have left to see?
It is incredible how the market for power meters has changed in the last 2 or 3 years. The arrival of new manufacturers has meant a real boom in the sector and, above all, a general decrease in prices. Now there is much more to choose from and at much cheaper prices than those that could be seen not many years ago.
And where is the sector heading? Once precision is no longer a problem, everything is heading towards offering ever cheaper prices. This is where consumers will start to benefit from the great increase in competition in the sector.
The major brands are beginning to have more than paid for their development investment and the new manufacturers are reaching a fairly mature market where there is little left to be discovered. There are already offers of power meters for only $299 (the last one is Tempo, which is conducting a collective funding campaign through Kickstarter).
In a few years (less than you can imagine) training with power in cycling will be as basic as training in running with a heart rate. The most basic options for measuring power (on one leg only and multiplying the power to obtain the total count) will have a totally affordable price for any cyclist, whatever their level. What before was only available to professionals, tomorrow you will be able to equip it all on your bike. And the most likely thing is that in not much time they will come as standard on the bikes themselves.
So go get your copy of the libro de Hunter Allen y Andrew Coggan «Entrenar y Correr con Potenciómetro» (the bible of power training) because sooner than you think, you will train this way too.
And with that... thanks for reading!