Big power discrepancies between Computrainer and PM

I am finding large discrepencies between my crank-based powermeter (SRM - calibrated before each ride) and my computrainer (calibrated before each ride with a 10-15 min warmup at ~150 watts and spin down test). In the past, using other platforms and Zwift in the past has resulted in a variance between my SRM and computrainer of 1-2%. The difference for the past 6 months or so can vary by as much as 20%. This typically happens at higher power levels (e.g., near the end of an FTP test above 320 watts) or on steeper climbs (>6 grades). For example, on the recent MAAP stage 3 climbs, Zwift was around 175-180 watts and my SRM head unit indicated 220-230 watts.

Do you have any suggestions to address this? It seems to result from slowdowns in wheel speed and overcompensating the resistance on the wheel. I would like to avoid buying a new trainer if possible

Thank you in advance.

You can use your PM for power and the computrainer for control. That way you have accurate data.

You can also use Zwiftpower to compare sources.

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Thank you Gerrie. Is there a way to get them back in synch so they are closer in power? The computrainer is brutal on the steep climbs where wheel speed slows down. I already go in to TrainingPeaks and pretty much delete the Zwift provided data because it is off by so much. I revert to my SRM data.

I don’t think there is a way to align them apart for a calibration. Search the internet and see if there is a advance calibration for the computrainer.

I would just use the PM for power in zwift it is more accurate.

I am not sure that the SRM broadcasts an output in the correct protocol (ANT or BLE).

I believe SRM not being ANT+ compatible was a reason many of the pro peloton have shifted over to wahoo and garmin devices.

are you using the direct connection of the computrainer to your computer to connect to Zwift? There is another option that may solve your problem. PerfPro has an ant Bridge program that works very well (can’t link to their site). You need to purchase the program which is rather inexpensive and as well you probably need 2 ant+ usb sticks. With this setup the Computrainer will transmit and receive as if it were an Ant+ FEC trainer. I doubt that Zwift is putting any further effort into updating or maintaining the Computrainer set up so something in an update may well have caused the problem you are seeing.