The PowerTap C1 Chainrings are the only chainring-based power meter on the market, as other crank-based power meters measure power at the crank spider. Not having to replace your entire crank offers numerous benefits. In addition, the C1 Chainrings feature dual-sided power measurement and transmit power data via ANT+ as well as Bluetooth SMART. The C1s are available in 53/39t, 52/36t and 50/36t chainring combinations for 5 bolt, 110 BCD cranks.
The C1s take a bit more time and effort to install than say a single-sided crank-arm or pedal-based power meter, as you have to remove the crank from the bike. However, you don’t have to mess with bottom brackets or the like – rather all you have to do is bolt the new chainrings up to your existing crank and you’re good to go. There’s really not much to it.
The PowerTap C1 Chainrings adds approximately 150 grams of weight to the chainring.
Left/Right Power Measurement
The PowerTap C1 transmits estimated left/right power balance. The C1 essentially “credits” either your right or left leg based on where in the pedal stroke you are at. It takes power from your left and right down strokes only, and ignores the upstroke. Since the majority of your power comes from the down stroke, it can estimate the power distribution fairly closely, just not exactly.
The C1 uses CR2032 batteries which are typical among most power meters. These batteries can be found in just about any store that carries batteries.
The C1 battery lasts for 200 hours.
Difficulty to Change
The battery can be easily replaced by removing the electronics cover which sits on the outside of the chainring (the black triangle shapped box with the PowerTap logo) using a 2.5mm hex wrench.
The PowerTap transmits data via both the ANT+ and Bluetooth SMART wireless protocols which means the power meter will be compatible with any head unit that supports these protocols. Note that in order to get left/right data, you will need a head unit that supports this functionality. The majority of head units produced in the last few years do so.
PowerTap claims accuracy of +/-1.5%. This is on par with the majority of power meters on the market.
To measure cadence, most power meters use either a magnet (which is attached to the bike frame) and a reed switch, or an accelerometer (a device housed inside the power meter which measures proper acceleration). In the case of the C1, an accelerometer is used. This is a nice touch in that you don’t have to worry about attaching a magnet to your bike.
PowerTap recommends that you perform a zero-offset before each ride. The C1 also has built in auto-zero that is triggered while coasting during your ride.
The electronics of the C1 have a 2 year global warranty. The chainrings are a wearable item and do not have a warranty.
Many users have experienced a break-in period of a ride or two, during which they might find the accuracy of the power meter to be a tiny bit off. Essentially, some of the C1’s hardware (bolts and fasteners) need some time to settle in and adjust. In order to accelerate the break-in period, it is advised that you perform a few short bursts, and follow with a manual zero offset. Note that this type of break-in period is fairly common amongst power meters and is not something to be concerned about – rather just something to be aware of.
When your chainrings get worn, you can simply purchase new chainrings from PowerTap without having to buy new electronics. However if you decide to change your tooth configuration, you should send the unit into PowerTap so it can be recalibrated.