Cycleops Magnus Accuracy

How accurate is the Cyclops Magnus trainer? I’m getting high power output, but I don’t know if it’s really accurate. I’m also relatively heavy, 198 pounds, so relatively high power output is perhaps not unusual. 

For instance, I can pretty much coast at a power reading in the low 300s from the trainer. I’m in pretty good shape; I used to run for an hour or more each day before switching to Zwift. But I’ve only been zwifting for a couple of months. I don’t have any basis for comparison, other than numbers I’ve measured for myself on the same trainer.

You would need a power meter on your bike to messure the accuracy of the trainer. Power meters are +/- about 2% and a trainer can be less accurate. Comparing a power meter to the trainer will be difficult because they will messure power in different place depending on the power meter used (pedal, single sided crank arm, duel sided crank, and hub).

300 watts is a high a FTP (I believe the average on Zwift is about 230) and if your doing that easily it sounds like something is wrong.  Running and riding use different muscles, but there can be some fitness carry over. Do you calibrate the trainer before you start a ride and about 10-15 minutes into the ride? 

I recently started using the trainer’s ANT+ connection more often, and the ANT+ connection gave me the opportunity to calibrate the trainer. So I did. The Zwift desktop app tells you to calibrate once each week, but I’ll calibrate twice each ride for a bit and see how it goes.

I think I’ll also get one of those crank-arm power meters and double-check; those are not too pricey if you avoid top-of-the-line. Thanks!

Christopher, I’ve had much better results by calibrating the Magnus through Rouvy instead of using Zwift’s in-game calibration. Doing it through Zwift has given me very unreliable results, including two times in which it’s been reading 2000 Watts with minimal effort from me.


Give Rouvy a try for better results. It’s the CycleOps-approved app for that. Good luck!