MPH a bit off on Spin Bike

Don’t hate me because I’m using a spin bike. I put the Wahoo cadence device on my shoe and what the display on my spin bike matches exactly as what Zwift is telling me. However, when I attach the speed sensor to the spin fly wheel (at the smallest/shortest rotation near the bolt) I get different readings. Zwift is about 4 to 5 MPH faster than what my spin bike reads.

Just for clarification: Peloton bike. And yes, I know my wattage won’t be right. I’m doing this for fun and as an experiment to see what extra use I can get out of my wife’s peloton bike before deciding to invest in a trainer setup.

p.s. maybe it doesn’t matter. It’s just for fun, for now. But I was hoping to get the MPH to match up like the cadence.

The cadence will match because different cadence sensors will report very similar RPM data, with some slop possible depending on the sensor’s location (flopping on shoelaces vs bonded to a crankarm).

Speed and power meters designed for an actual bicycle wheel of industry-standard sizes won’t necessarily work as intended when attached to an exercise bike’s solid flywheel because wheel sizes aren’t the same, or even standardized within the exercise equipment business. A few MPH variance is to be expected. Don’t sweat it too much, and enjoy.

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Got it. Thanks.