I just picked up a second hand Kickr v4. I am not particularly knowledgeable on the technicalities of bikes but it came with an 11 speed cassette and my bike has a Shimano 9 speed. I am pretty sure I need to replace the cassette on the Wahoo to a 9 speed to match the one on my bike but do I need to also match the sprocket size or can it be any Shimano 9 speed cassette?
Welcome to the forums @leopeo
This article ought to help
It must be compatible with your rear derailleur, e.g. not too large sprockets (think MTB cassette on Road Bike). Other than that, every cassette should do.