Calibration question

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Outlaw Hobbs

Senior Member
Location
Herts
Tried a search but couldn't find the answer to this.
I have a Tacx Vortex and the Tacx utility app on my iPhone. If I use the Tacx app to calibrate the trainer and then connect to Zwift should I then calibrate using the Zwift calibration option on the connection screen as well?
Up to now I have done both calibrations but yesterday I only used the Tacx app and then just connected to Zwift and started a group ride. It seemed to me that I was putting out a bit more power and was rewarded by Zwift with a 'FTP increase detected' from 200 to 209W. Is it likely that I'm now a Zwift doper or is the power calculation more accurate this way? Obviously I hope it is the latter.
 

bridgy

Legendary Member
Location
Cheddar
I'm not sure entirely because I don't have to calibrate my own trainer but I would think if you've calbrated on the Tacx App that should be enough - I think the Zwift calibration is just there as an alternative option to the app, or for trainers that need calibrating but don't have a specific manufacturer app for it.

On-wheel smart trainers like yours are not particularly accurate with regards power compared to the higher end direct drive trainers or a decent power meter - variables like temperature, tyre pressure and even the type of tyre can all have a big affect. The Tacx Vortex only claims accuracy to within 5% and the 9 watt difference you saw is within this tolerance so it doesn't necessarily mean anything.
 

si_c

Guru
Location
Wirral
I would calibrate one or the other not both. I had a Tacx wheel on trainer and my calibration process was to warm the trainer up for 5-10 minutes and then perform the calibration, this gave me consistent readings for power - I wouldn't worry about accuracy so much as consistency as far as training goes. I would do this once a week or so rather than every time I used it and just kept the same tire pressure between sessions.
 
OP
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Outlaw Hobbs

Outlaw Hobbs

Senior Member
Location
Herts
Thanks both. I was lucky and bought the trainer at a great price from a fellow club member who was upgrading.
It's almost new and works well. I'm using a trainer specific tyre and am fastidious about warming up and checking tyre pressure before calibration.
It's true that precision is more important to me than accuracy since the objective is to train up in the winter and hit the ground running when the TT season kicks off.
Think I'll just use the Tacx utility app to calibrate from now on and see how the numbers look.
 

Ming the Merciless

There is no mercy
Location
Inside my skull
No need. The calibration is essentially about getting the pressure on the rear wheel in the right range so it doesn't slip but also doesn't have so much pressure making the wheel turn impossible. You only need to do it if the bike has been taken off the trainer. If calibration consistently has it in the green zone youre in the right place. I found if I haven't removed the turbo tyre between putting back in turbo then calibration shows it in the same place for at least next 2/3 sessions. Make sure you keep turbo tyre at a fixed pressure each time.
 
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