Currently, there are indeed a few options for a Shimano Ultegra R8100 crankset. However, this groupset is still new and we expect there to be more options available as we get into 2023 and other power meters that fit this groupset are released.
Left Crank Arm Power Meter
4iiii and Stages Cycling both make crank arm power meters for Shimano R8100. You just swap out your current left crank arm for the new power-equipped one and you are good to go. These power meters measure power from your left leg and double to value to approximate your total power.
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 and 4iiii PRECISION 2 power meters and 8 mm of clearance for 4iiii PRECISION 3+ 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
Crankset Power Meter (Spider Based)
power2max ROTOR ALDHU Road Power Meter Crankset (staff favorite)
This is a new crankset (power meter spider, crank arms and spindle), excluding chainrings. power2max makes wonderful power meters. They measure both left and right leg power, are reasonably priced and are as good as it gets in terms of reliability. If you select the 24MM spindle option, it will fit your current bottom bracket exactly like your Shimano crankset (no need to change bottom brackets). In addition, if you select the Shimano 4-Bolt spider, you can even use your Shimano R8100 rings on it.
The Sigeyi power meter crankset is very similar to the power2max above. It is a spider-based power meter that measures power from both legs and will also serve as a direct replacement for a Shimano R8000 crankset. It is accurate to within +/-1.0%, is lightweight and features a rechargeable battery. However, it is a bit more affordable than the power2max.
This too is a new crankset (power meter spider, crank arms and spindle) and can be purchased with or without chainrings. The INspider measures both left and right leg power, comes in a variety of crank arm lengths and can be set up in a 1X or 2X chainring configuration. This power meter can also be purchased with a 24MM spindle so it will fit your current bottom bracket without any changes. You can use your current Shimano 8100 chainrings on it or buy new ROTOR rings.
Pros: Moderately priced, VERY reliable, measures both legs
Cons: Have to change your crankset
Crankset Power Meter (Crank Arm Based)
4iiii, Stages and Shimano make complete dual-sided R8100 cranksets. With these power meters, you get a new Shimano crankset with a power sensor attached to the inside of the left and right crank arm. Therefore, they are able to measure power from both legs as well as tell you how much power each leg is producing individually.
Please note, as with the left side power meters above, you need to confirm you have 10mm of clearance between the left crank arm and the chainstay in order for the sensor to clear.
Pros: Measures both legs, provides independent left/right power
Cons: Have to change your crankset
Power Meter Pedals
Power meter pedals can be installed on any crankset. They are reliable, accurate, easy to install and can be moved between bikes. We carry every power meter pedal available including ones from Favero, Garmin, SRM/LOOK and Wahoo. This includes both single- and dual-sided versions as well as pedals for SPD-SL, LOOK Keo and Speedplay cleats.
Pros: Easy to install, works on any bike, can move from bike to bike, don’t have to change crankset