Power measurement is one of the optimal tools for training. Currently, systems are based on the hub, cranks or pedals. Each has its advantages and disadvantages, but for the truest readings and a robust design, we’d opt for cranks.
SRAM’s new Red Quarq is simple to set up – it’s as easy to fit as a standard chainset, and uses one of three supplied magnets for cadence information. Just spin the cranks to wake it, then pair with an ANT+ compatible head unit (not included). Pairing is easy, as SRAM have printed the ID code on the spider. A simple zeroing process follows (spin the cranks backwards four times) and you’re ready to ride. SRAM recommend zeroing it regularly over the first dozen or so rides.
The heart of the device consists of five strain gauges in the spider, and a separate magnet. These measure torque and angular velocity, which is converted into a power measurement. It can also gauge the left/right power balance, the sort of analysis that usually requires gym-based equipment.
The left/right split power data is displayed on the head unit. This shows the ratio of the power in the right-side drive stroke (first half, 0 to 180 degrees) to the power in the left-side drive stroke (second half, 181 to 360 degrees) for each revolution. This is especially useful if you’re experiencing any pains or tightness in a single leg or you’re returning from injury.
We compared the Quarq against two PowerTap G3 wheels to see how consistent the data was. Initially we were concerned over power differences varying from 5 to 15W with the first G3 wheel, though testing against the second wheel showed a closer match – between 5 to 7W higher for the Quarq, about what we’d expect between the crank spider and the rear hub through drivetrain losses.
To get accurate readings you have to zero the meter at the start of your ride, as the strain gauges are temperature sensitive. Without this zero offset, figures for a hot summer’s day and a freezing winter’s day can differ hugely.
This zero offset can drift within a recommended range, though Quarq assured us it isn’t strictly necessary to stay within the range (ours didn’t) as long as the numbers remain relatively stable, which ours did.
We can’t be absolutely sure which of the three power meters was most affected by temperature drift, but the Quarq’s consistency with the second PowerTap is reassuring.