There are several power meters that will work a Cannondale road crankset:
Left Crank Arm Power Meter
Stages Cannondale Hollowgram Si Power Meter
The Stages power meter is compatible with 2014 or newer Cannondale Si, Hollowgram Si and Hollowgram SiSL2 cranks. It is also compatible with the Cannondale One crankset.
Stages Cannondale Hollowgram Si Power Meter
Please note, these power meters attach a sensor to the inside of the left crank arm. On some bikes, there is not enough room between the left crank arm and the chainstay for the sensor to clear the frame. Therefore, you should make sure you have at least 10 mm of clearance for Stages power meters. Also, please make sure that you don’t have a bottom bracket mounted rear brake (used on some aero and TT bikes). Please refer to the image below.
Pros: Affordable, easy to install, don’t have to change crankset
Cons: Measures left leg power only
Spider Power Meter
power2max Cannondale Road Power Meter
This power2max power meter is compatible with all models of Cannondale’s Hollowgram cranks: SI, SISL, and SISL2. It is also compatible with the Cannondale One crankset.
power2max NGeco Cannondale Road Power Meter
Please note, some Cannondale cranksets have a 120 BCD (which is usually indicated on the outside of your chainring). If this is the case, you must purchase new 110 or 130 BCD chainrings to use with your power meter. We recommend Praxis chainrings with this power meter.
Praxis Works Road Standard Chainring
Pros: Moderately priced, VERY reliable, don’t have to change crankset, measures both legs
Cons: None
Power Meter Pedals
Power meter pedals can be installed on any crankset. We have several models to choose from.
Pros: Easy to install, works on any bike, can move from bike to bike, don’t have to change crankset
Cons: None