Powermeters


Data is knowledge and control

HOW DOES IT WORK?

A power meter measures Watt. But how, and what does it do exactly? Power is a result from the formula: speed x strength = power. Meaning the rotation speed of the crank. This is easily done with a cadence sensor. Strength is a somewhat more complex thing to get in to. This is measured with so called strain gauges. These strain gauges are thin flexible strips with a metal pattern. When strength is applied to the pedal, the strain gauge is stretched out. This causes the metal pattern on the strip to alter. The electric charge that is constantly applied to the strain gauge causes this. The bigger the stretch, the bigger the strength that is being applied to the pedal. Increasing your power can be done a number of ways:

  • Apply more strength to the pedal. This can be done using a lower gear.
  • Pedal faster. The length of the crank can be influenced by this.

ADVANTAGES
The advantages you get when training with a power meter are huge. We have compiled a few of them.

  • You exercise more effective. It will instantly show your progress while your heartbeat is a product of the workout that is being done.
  • You can do a series of sprints using a lot of power with long recovery time without your heartrate going up high, all this while working out hard. Luckily your power meter will tell you this too!
  • You can keep better track of the physical shape you’re in as well as noticing when you’re in need of an extra workout, or when you need to take a break.
  • Your strengths and weaknesses become visible, allowing you to exercise these and thus improving your workout.
  • You yourself can do a fitness test. This way you can measure and compare your overall fitness with other cyclists around the world. This will even save you from getting several lab tests.
  • Aside from the advantages just discussed, your trainer or coach also has a better understanding of the progress you have made thus far. And incorporating this into future workouts.

TYPES

Power Meters can be applied to various locations on the bike. Each locations has its pro’s and con’s. Below we will explain each location, and what it does exactly.

MEASURING IN THE REARHUB
Some power meters are located in the hub of the rear. By applying strength to the pedals the hub is put in motion using the crank arm, spider, chain ring, chain and cassette. To get this to work an amount of power is needed. This power is measured through the torsion that takes place within the hub during cycling. The amount of torque is equal to a certain amount of power that is determined beforehand. This amount of power is transferred via a wireless protocol (ANT+ or Bluetooth) to a smartphone or computer. These have to be linked first, so as not to have any interference with any other devices. The hubs are available to mountain bikes, race (time lapse) bikes and track bikes. Every power meter can be swapped on and off other bikes without applying difficult actions. That right there is one of the big pro’s. The pricing is very competitive as well, compared to other manufacturers. A con is that during a match you will often use a different set of wheels from the one you will be training with. You then miss out on essential data that could make a difference. Powertap is currently the only one offering this type of measurement.

MEASURING IN THE PEDAL
The first place pressure is applied to during cycling is the pedal. Several manufacturers consider this to be an ideal location for measuring. Manufacturers like Garmin and Polar have a power meter located in the pedals of the bike. A construction that is easily swapped between other bikes. The measuring is done very accurately because no strength is lost in the ‘drivetrain’. Where measuring the power in the rear hub does lose some strength in the process. Powertap and bePRO both manufacture power meters that are located in the pedals of the bike.

MEASURING IN THE CRANK ARM
It might just be the most common way of applying a power meter on to the bike. The bending the crank arm makes (left or right) is registered and linked to the amount of power that is needed to do this. Again strain gauges are used to register the amount that is being bend, which is passed on through to the head unit. The big pro when measuring this way is that it itself adds very little weight to the bike (Around 20 or so grams). Adding to that is the fact that you can use it with every set of wheels you ride with. Resulting in more data to work with, which then again gives you a better analysis. Another thing is that you can easily measure left or right separately. The con is there not being all that much crank models to choose from. Especially carbon cranks are in very limited supply with this way of measuring. Therefore you could imagine having an aluminum crank on the left, and a carbon crank on the right. Manufacturers are Rotor, Stages, Infocrank and Pioneer.

MEASURING IN THE CRANK SPIDER
This is where it all started. 25 Years ago SRM developed the first power meter where the strain gauges were made into the spider. By hiding the electronics into the spider, it is greatly protected against the impact of a crash. This ensures a system that will last, and stay accurate for a long time. The broad choice in cranks that is supplied by SRM and Power2Max make this particular system very popular, despite it weighing a little bit more. That again is also a con. Having said that, there are so much crank models and bottom brackets to choose from that there is always a solution on hand. Quarq also takes advantage of this technique and uses it in her own MTB cranks. Any more convinced by your own product you cannot get!

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