Basic Guide To Power Meters

First off, what is a power meter? A power meter is an electronic device for your bike that measures the amount of energy it’s costing you to move the bike forwards. This is measured in watts, much like a lightbulb. A power meter uses strain gauges to measure torque and velocity, while a small onboard computer uses an algorithm to calculate how many watts you’re using to power the bike.

On a purely cost-benefit ratio, aside from your bike, a power meter is the best investment you can make in yourself as a rider. A power meter has certain advantages over other methods of guiding your riding, like speed or heart rate, since power isn’t effected by terrain, wind, or nutrition. Since it’s a measure of raw output, 300 watts will always be 300 watts worth of effort, no matter how fast or slow you might be going due to conditions around you.

A power meter is the best and most reliable way to guide your fitness improvements on the bike, whether you’re doing structured training or just out to ride for fitness. A power meter won’t make your bike faster, but it will help you—the engine—be able to make your bike go faster.

Since this usually comes up, we’ll address it upfront. Yes, power meters are expensive. However, with new entries to the market and improvements of technology, the price is coming down almost monthly. Does everyone need a power meter? No, absolutely not. Cyclists have ridden for generations without them and gotten plenty strong. But just as we embrace new technologies in bikes like carbon fiber or indexed shifting, so should we embrace new technologies that improve the engine that drives the bike. As we said above, we believe from personal experience that a power meter has the best return on investment for any upgrade you can make to your bike.

So if you’re ready to take the plunge into power, which kind of power meter is right for you? Good question, there are a few different options out there, and determining which is appropriate for you will depend on a few things like budget, experience level, and how much you love data.

 

Crank Based

Crank based power meters are often touted as being the most reliable and accurate. Crank power meters place the power meter in the spider of the crank, where the chainrings bolt on. This has the advantage of allowing the strain gauges (which measure power) to be very close to the power input (your legs). They are also compatible with just about any bike, so long as you have the right bottom bracket adapter.

Examples: Quarq, PowerTap, SRM

Pros:

  • Extremely Accurate (usually in the +/- 1.5-2% range)
  • Reliable
  • Broad compatibility

Cons:

  • More expensive
  • Relatively heavy
  • Can be difficult to install if you have to change out your bottom bracket
  • Can be difficult to change the batteries on some models

 

 

Crank Arm Based

An evolution of the crank based power meter is the crank arm based power meter. This puts the strain gauges directly into the crank arm itself—usually the left or non-drive side arm. These are definitely among the easiest to install, and are by far the least expensive models. The accuracy is a little less refined compared to some crank based power meters, but not terribly so, and they are available for most alloy and some carbon fiber cranksets.

Examples: Stages

Pros:

  • Very easy to install
  • Inexpensive
  • Work with the crank you already have
  • Broad compatibility
  • Lightweight

Cons:

  • Slightly less accurate (usually in the +/- 2-3% range)
  • More limited temperature compensation (important in the summer/winter)

 

 

Pedal Based

A newer entry to the market, pedal based power meters place the strain gauges and electronics on the pedal spindle themselves. The manufacturers claim that this type of power meter is the most accurate, since the strain gauges are closest to the legs with minimal distortion in the materials in between. They are also extremely easy to install, and easily moved between bikes.

Examples: Garmin, PowerTap

Pros:

  • Very easy to install
  • Excellent accuracy (usually in the +/- 1.5-2% range)
  • Vectored power (can tell you where in the pedal stroke you’re most efficient)
  • Easily moved on to different bikes
  • Lightweight

Cons:

  • Pedal strike is a danger
  • Limited to Look or Shimano cleats (no Speedplay or Time compatibility yet)
  • Road only for the time being

 

 

Wheel Based

Wheel based power meters are some of the least expensive and easiest to use power meters around. On a wheel based power meter, the strain gauges are placed in the rear hub where there is plenty of room for the electronics. While inexpensive and easy to install, wheel based power meters do have some limiting factors, but are an excellent choice for riders looking for an easy entry to power meters.

Examples: PowerTap

Pros:

  • Very easy to install
  • Inexpensive
  • Easily moved on to different bikes
  • Lightweight

Cons:

  • If you change out wheels, you lose power measurement
  • Can be difficult to change batteries
  • Accuracy can suffer due to frame flex
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