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Stages left-crank-arm power meter is virtually invisible – to the eye and to the scale(Image credit: Ben Delaney / Future Publishing)

This article originally published on BikeRadar

The design is quite simple in appearance and in concept – but complicated to execute. Stages measures power on the left side and doubles that figure for an ANT+ signal readable by head units such as Garmin’s Edge series, and a Bluetooth 4.0 signal for smartphones. There are no magnets to attach to your frame or additional sensors to ziptie on. A metal left crank arm for Shimano, SRAM or FSA simply bolts on your existing compatible crank. Clean and easy. At less than 20g, it is also the lightest real power meter on the market.

When out on the road during group testing of multiple power meters, we were often asked which one is the most accurate? Without a lab, we simply can’t answer that. We can only tell you the patterns and trends we found among the meters we tested. Stages, like the others, was consistent. Like with most power meters, we found Stages meters to have certain personality traits. For one rider, the data was consistently level with PowerTap meters but higher than an SRM and a set of Vector pedals by 5 to 10 watts, in most conditions over most distances.

Stages is betting the farm that one crank arm’s data, doubled, is good enough for most riders. Most people have similar power output between their two legs, Stages argues, and installing strain gauges and other componentry on one arm instead of both keeps the price down. For us, long-term data from concurrent Vector testing showed that left/right power output varied by about four percent in one rider over the course over several months. Yet during that time the primary metrics of average power, kilojoules and others tracked in a highly similar manner, with Stages’ data nearly always being slightly higher than that of the Vector (and SRM).

We appreciated the visual cleanliness and ease of use with the Stages meter. Unlike SRM or Quarq, which require a magnet to be attached to your frame, Stages uses an accelerometer to trigger power measurement and measure cadence. Perhaps because of this, however, there is a split-second lag in the initial power reading when you begin to pedal. All power meters have a bit of a lag – in part because of ANT+ protocol – so Stages' lag was only noticeable when a row of Garmin Edge computers on the handlebar showed one number pop up a fraction of a second before another. All that to say – this is splitting hairs.

Once paired with a head unit, the Stages power meter works like any other good meter. You get a steady number on your screen, because data is captured four times a second and the average of this is transmitted on ANT+ once per second. In addition to the basic power measurement, Stages also now gives you torque efficiency and pedal smoothness, two metrics that have been introduced with the Garmin Edge 510 and 810 computers. There is no left/right measurement, of course.

The Stages meter is remarkable in that it broadcasts in ANT+ and Bluetooth Smart. Most power meters use ANT+, as do most head units. With Stages, you can also record power data with smartphone apps like Strava or Wahoo Fitness. We had mixed experiences with the Bluetooth. While Stages would connect to Strava or Wahoo Fitness every time without problem, the phone sometimes lost the signal when we put it (iPhone 4s and 5) in our jersey pocket. This happened for a couple of riders, but some had no problems. When riding with the smartphone in a handlebar holder, the Bluetooth power data was uninterrupted.

Although Stages’ parent company has been making crank-based power meters for gym bikes for years, the Stages brand and product was introduced at the end of 2012. As such there were a couple of hiccups with a few early batches of product, including a faulty epoxy and batteries. Some riders experienced very short battery life, perhaps because water snuck into the unit. Stages insists that these problems have now been addressed, and any customers who had issues were offered replacements.