I have two images, one is the Strava / zPower power file, the other is my SRM. Speed/power lines are the same for zPower so the power line in Strava should be identical to my SRM speed line. However you can see how as the fluid warms up the resistance increases significantly.
My 220-234 SRM watt intervals showed up as about (I used Strava’s “click a segment to get avg power etc so it’s not quite as precise”) 173-191 zPower watts.
I understand this is a known issue, I just wanted to put the images out there so you can see how they compare to what you’re finding. This is the first time I actually saw and experienced the “distortion”. Before I wasn’t paying enough attention to see it.
I use a cycleops fluid2 as well and just this week I started getting the flashing Tire Slippage warning with erratic power fluctuations. Prior to this week (for 2 months of transporting to Zwift Island 3 to 4 days a week) the readings were very stable and consistent. I’ve used the same setup from the beginning. Has anyone noticed any recent problems?
I am using a Fluid 2 with a Power2Max. I use the Power2Max power for Zwift, so I am unaffected by the power drift, but I agree that effort at cold is less at the same wheel speed than later on, and can further change even when warmed up if a higher sustained power is maintained at any point.
If there are any experiments Zwift is interested in seeing results for I can try and help get additional data points.
