Speed & Watts inaccurate (TACX Vortex)


I’m using a TACX Smart Vortex T2180 with an iPad mini V5. All running the latest firmware.

My issue is this I’m pedalling at 100rpm in a 53/12 gear yet the Zwift app is claiming I’m only putting out 50 Watts and pedalling at 8km/h or something close to that. Meanwhile in the real world I’m creating so much heat on the trainer that I’ve actually singed the rubber on my tyre so obviously the app isn’t interacting with the trainer properly.

Can anyone offer some advice please ?

I’ve calibrated the trainer using the TACX app, tyre pressures are 100psi on a 700c x 23 and updated the trainer firmware. The Zwift app sees my trainer and I can pair it to the app but the simulated cycling still does not represent my performance in the slightest.

I’m at a loss where to go next.

Hi @Gordon_Borland

Do you pair the trainer as a power source and controllable?

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Yes I believe I did.

When I used my vortex and calibrated it with the phone app I always made sure the roller tightness was right up against the “Too Tight” line in the app. If the tire is slipping that will cause the watts to under-report.
Half way between “Too Loose” and “Too Tight” never worked for me.

Ride for 10-15 min to warm the tire first and then calibrate using the app.


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What he said. Definitely set that bar slightly towards too tight. Overall, pretty bummed with this calibrating…

Yup Definitely. Just confirmed it. I’d post an image (jpeg) showing this but the forum says I can’t embed a media item. Ah well…

Previous post was in reply to making sure I’d connected as a power source and controllable. It seems to have got out of sync.


I’ve had some success thanks to your suggestions of re-calibrating the trainer towards the too tight end of the acceptable range. I’m not hard against the calibration too tight limit, but that definitely seems to have improved things. I’m seeing watts and speed that are a rough approximation of what I think I’m doing on the trainer itself plus I can overtake riders then coast and see them over take me so the trainer is working with the app. Would the accuracy improve if I placed my calibration closer to the limit ?

Now I just need to ride a hilly course to see if the trainer adds and removes any resistance to simulate gradients.

Thanks for your help and assistance!