Hi, I have a Xplova Noza S as a base and power meter. Recently, I bought a Stages left crank power meter. When I compare the data after a race, I find that the average power from the two sources can differ by as much as 25 Watts. It tends to be worse if the race was hard. And typically, the two powers start pretty much the same and then they diverge more and more as the race progress. My curent hypothesis is that when I tire I tend to use my right leg more. What do you think? Anyone else experience something similar? I am worried that my base is not reliable now. Here is an image of the two datasets in the next post.
you need a 3rd and 4th power meter to know what is really going on… maybe even a 5th
1 Like
This is quite possible. If you had a way to measure left/right balance that would help you understand it.
My other hypothesis is that the base heats up as the race progresses and then slowly drifts away from accuracy.
lots of trainers can have drift like that at higher wattages and combined with lower cadence.
1 Like
It is not really higher wattage or lower cadence. The difference gets bigger with TIME.
My experience with Stages power meters from when i had a Stages Bike… is that they are quite crappy 
You have to make sure that the crank arm(s) are in the correct position when calibrating, and also make sure to calibrate again after 30 minutes of riding.
But as someone wrote, you probably need 1 or 2 additional power sensors to get an idea of which actually shows what you think is the correct data 
BòóX
1 Like
Haha! Not sure the peloton will wait for me when I stop to recalibrate after 30 minutes!
Xplova is probably drifting heating up, and the single sided will never be accurate…..being single sided.
As they overlap quite good in the start, the stages is still probably the most accurate…..If that is a word that can be used to describe a single sided pwr mtr
If you are right about the heat drift, then it means that I am cheating (unwillingly) in every race I enter. Do you imply that any trainer would drift too and we are all cheating? I find it hard to believe that the designers of the trainer would not have taken heating into account knowing that all the power that the rider generates turns into heat.
Not calling it cheating, and powerdrift is really not that uncommon.
As there are quite big differences in accuracy, some races exclude trainers that doesn’t meet certain standards.No need to take my word for it, there are several reviews stating it over reports
GP Lama «You will not be using this in Zwift races, or you will possibly be accused of cheating»
Ok I have digged a little more into this. Watched the GP Lama video review of my trainer. It really seem to be a heating problem. I have read someone suggesting a calibration at the end of a race when the unit is hot to counter the problem. I will try that. I’m also buying a crank based power meter to get another opinion… I hope I don’t have to buy another trainer. Really don’t want to feel like a cheater.
Yeah it doesn’t look good. I wonder what would happen if you kept a small high-power fan aimed directly at the trainer. It could possibly reduce the drift a bit.
Yes. Good idea. I will try that too.
The curves really look like a heating issue.
How long do you warm up before the ride?
I typically only ride in the Winter in an unheated garage so there is a warm up period then my trainer seems to stablize after a 15 - 20 min warm up.
In 2021, because of Covid, I did Zwift more into Spring and Summer and I suspected my trainer was continue to warm up because it seemed the watts were easier.
This was before I had power pedals so I don’t know what my power actually was.
I had an extra fan and I directed it to my trainer and it seemed to help.
Not sure what hemisphere your in but if it is warming up in your area, you might want to put a fan directed on the trainer.
I just read Paul’s less wordy response.
I agree!!
Now knowing, you will move to cheating (knowingly) in every race 
A fan might help a bit, but it will still heat up, and it will still vastly over report in sprints etc.
For Zwift that is totatlly OK in most scenarios except elite races. You know you get a boost, as many others do with other trainers. Demanding 100% accuracy would exclude 2/3 of the zwift population from events.
As for me, I’d like to see at least a few races with stricter hardware requirements and native dual readings
It would exclude 100% of the users from events, no one has 100% accurate equipment.
Now that I know I will not keep going this way for sure. I am not elite by any means, but my racing score is around 900 and I manage to podium when real strong riders are not attending or are having a bad day. When I bought this trainer, I had not the slightest idea I would enjoy Zwift racing as much as I do now. I’m an outdoor guy so riding in my basement didn’t seem like something I would enjoy. But winter is long here in Quebec. The good thing is that the oudoor season is here now. That will give me some time to deal with this before next Zwift season.
2 Likes