Schwinn ic8 power display - TacX v Zwift

I am wondering if the IC4/IC8 power output problem (reporting too high) is actually a Zwift issue and not a problem with the bike. I tried the following using the TacX Training app and then using Zwift:

Ride at average cadence of 60 rpm for approximately 11 minutes, resistance level 40 set on bike. I got the following results:

Distance 5.95 km
Duration 11:21
Avg speed 31.5
Avg RPM 60
Avg HR 104

ON ZWIFT (2 sets of results)
Distance 6.63 km 6.17
Duration 13:19 11.03
Avg speed 30 33.5
Avg RPM 55 58
Avg HR 95 115

As you can see, the power figures displayed on Zwift are approximately 100W higher. I acknowledge that there is a margin of error in here (the TacX was a flat run, and I set the gear selector to 1, on Zwift I was in NYC and so some slight inclines) but I do not believe that accounts for a power difference of approximately 70%. I was working at the same levels in all cases.

The power reported from the TacX app seems far more believable than that from Zwift. Is it worth someone else verifying these results? I would be interested to have some feedback. Cheers

Hi Chris,

Zwift only display what is set to it.

Can you record on Zwift and the Tacx at the same time, then you analyze the results using.

Hi Gerrie,
No, I am unable to connect 2 apps to the bikes’ Bluetooth sensors at the same time. Its either one or the other.

Just to reiterate, why should Zwift display a power figure 70% higher than the one displayed on the TacX app, given that all other factors were similar (average Cadence, average speed, average HR, distance). It would imply that Zwift is inflating the power figures from the bike.

(I have also posted in the Bugs and Support category).

The Scwinn spin bikes do not use a real power meter and therefore useless for accurate reporting.

That maybe the case, but if similar data is being sent to the TacX app as to the Zwift app, why the difference in displayed power (133W on TacX, 234W on Zwift)? Is it not to do with Zwift’s interpretation of that data?

I don’t know what wizardry Scwinn does with its data but Zwift doesn’t manipulate data sent to them.

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Zwift also does not include these bikes on their list of supported indoor bikes. Schwinn makes the claim that you can use them for Zwift, but they leave out the part about the inaccuracy.

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Maybe I missed it but, question, do you HAVE that nice lightning bolt near your name when riding in Zwift?
Because if you don’t, you’re just pairing the wrong sensor.


Yes, I do.