SRM Power Meters and Tacx Trainers

[Dgas]

Just had a SRM power meter installed on my bike, brought it home yesterday evening, to try it out and get used to all the readouts from the head unit, stuck it on my Tacx trainer. I have I Vortex which connects to a PC and gives me a number of read outs, amongst those, speed, power, cadence and distance. Speed was a bit different but not by much. Cadence was spot on. Distance differed a bit, possibly due to the different speed read out. Power was wildly out by at least 50 watt. I have not plotted it, but would assume that the higher the power output the greater the difference.

 

My qustion is, has anybody experienced the same? I am assuming that my SRM unit is correct and the TACX is out. The SRM unit was calibrated by Active works before being put on the bike.

 

Is there any way to calibrate the Tacx unit to be the same?

[Broker]

Experienced the same with my Stages and Tacx. Tacx reading was at least 20 to 40 watts higher. I don't know of any way to calibrate the Tacx to give similar readings than the on bike power meter.

[shaper]

Think maybe you have to calibrate the break , see page 6 https://www.tacx.com/Media/Default/Manuals/TTS3/en/3_De%20functie%20knoppen/De_functieknoppen_Instellingen_en.pdf

[Dgas]

Think maybe you have to calibrate the break , see page 6 https://www.tacx.com/Media/Default/Manuals/TTS3/en/3_De%20functie%20knoppen/De_functieknoppen_Instellingen_en.pdf

Thanks, will try that tonight. Also spoke the SRM agent in SA, they suggested to make sure the "slope" on the SRM system is set right. Not sure what that means but will check it when I get home.

[Ryno.]

What is the accuracy they specify on the Tacx trainers? I think stages has 2% accuracy

[Keithc]

In my opinion, the Tacx trainers have never been very accurate in the Power Readings. I changed from Tacx to Cycleops a while back for better acuracies.

[Skinnyone]

You will always see a difference in readings between a crank based or "on board" PM as opposed to the power readings from the IDT as generally the IDT is a calculated value meaning there is generally no direct measure strain gauges, as well as the fact there will be losses thru the drivetrain of the bike and wheel/tyre thus giving the two different values.

 

CycleOps are probably the closest as they are owned by the same parent company as PowerTap so there is close in house technology sharing to get the best possible readouts...

[Dgas]

Has anybody used the Computrainer? I went to test one out today at ActiveWorks and I walked away with a 'wow' that is different. The price is a big steep at 26k. Compared to the Tacx trainer I am using now, there is a major difference. The resistance feels like you are on the road and the Watt numbers were very similar to that on the SRM.