Power v Calibration

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Power v Calibration

Postby haigh.ian » Thu Mar 26, 2020 10:35 am

If the calibration is down (the calibration test numbers is less than the number written on the trainer) will it affect the difficulty and/or power reading?

I ask because written on my trainer is 6458, but my calibration was 6452, ie 6 down. After tightening the adjuster bolt the calibration is now correct 6458, however the trainer feels much more difficult to drive the same wattage. For example at the same heart rate I'm pushing 50-70 less watts than I was before I tightened the adjuster to fix the calibration.

I'm not questioning the new power readings with the correct calibration, I'm asking if with the calibration incorrect (-6), would this lead to easier efforts for the same power, or higher power readings.... important because all of our FTP, training plans, training history, etc is based of our power outputs.

Could someone tell me how the calibration/belt tightness affects power readings/difficulty? I've posted on Facebook, nobody thinks calibration affects power, but I can feel a big big difference, it almost feels like there is more resistance, like I have the brakes slightly on. Note that I changed the belt about 5 months ago.

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Re: Power v Calibration

Postby mark.lovibond » Thu Apr 09, 2020 10:03 am

Hi there Ian,

It would appear that the calibration numbers work in reverse to power value. My Elite Direto was reading high power values compared to my Stages and Vector power meters which I used simultaneously on the same bike to confirm which reading was incorrect. I performed the calibration and my figures were down also, the difference in my case was about 20W-30W through a 80W - 200W range. Using the belt tension adjuster, as I increased the calibration value the power wattage figure came down.

Obviously for me, this now means that I am having apply more effort to achieve the same values as before the adjustment and therefore what you are experiencing appears to be correct.
If you have a friend who can loan you a power meter or use their power meter fitted bike on your Direto you could perform a similar test. Obviously you do want to be sure that the non-Direto power meter is reasonably accurate first. I did this by using a Powertap wheel, on a wheel-on trainer with Stages crank and Vector pedals all at the same time and all their readings were within about 5W of each other.

However, while we are in lockdown and you only have access to this one device for powerbased training, do a FTP test and use those figures for all your training on this device. I don't worry about other peoples wattage figures as you dont know whether they are accurate or not, they might be operating on an out of tolerance device themselves. What is key in consistency in your own training so you need to ascertain that baseline for your body and your training devices.

The issue of accuracy might come when this lockdown is over and you pop to the gym and train on another device like a wattbike. but who is to say that the wattbike figures are accurate? This is where you either do a separate test on the wattbikes or simply train to HR values that you achieve on your home trainer for specific wattages.

Look forward to hearing your thought on the above ramblings



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Re: Power v Calibration

Postby bianchetti.paolo71 » Wed Apr 15, 2020 9:22 pm

I've just replaced the belt and I've done a calibration. I did the calibration after 10' riding. I matched the offset target 6133. I performed 90' ride and the I double checked and I noticed that the value dropped down to 6128.
Is that normal, did you have the same experience ?

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Re: Power v Calibration

Postby Elite Admin S » Thu May 21, 2020 10:10 am


A little decrease of the offset is normal, is the belt adapting to the mechanic of the trainer.
If the value decreases further (more than 5 points) AND at the same time you have any issue (noise, slipping at high power, sudden drop of power), it is necessary to tightening the belt


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