dorongo wrote:
Recently got a Quarq Dzero.
I always though the Stages power numbers I had before it were high, but the quarq is massively lower (about 20w).
Comparing it to Tacx Neo it is about 10w lower.
I did not do (nor do I know how to) a physical calibration, just installed it and zero-reset at the start of every ride.
Has anyone else experienced similar issues
Your Quarq is the only thing i would trust, here is why:
Stages make a good power meter with one significant assumption: that total power = 2 x 1 leg power output, this assumes a constant 50/50 balance between your legs. Most people will have a power balance difference between legs that can vary with exertion levels etc. This could lead to power depression or elevation.
Every Erg trainer i have ever used will read slightly high, except for the Elite drivo which was dead on compared to two different power meters. The key is does this number remain constantly 1-2% elevated, if so that is no big deal as you just make the adjustment. My power beam pro was always 2-3% elevated, the computrainer was always 2% higher, and the Kickr was always 3-4% high. Obviously at 400w that will seem like a bigger difference than at 150w, but the percent difference will be the same. I always used the Quarq to record power numbers from a training perspective and just used the trainer to control resistance.
Finally all power meters will have a percent accuracy. I think Quarq states 1.5% on the aggregate. Most Erg trainers have stated power accuracy levels around 5%. Finally stages might measure to 2% accuracy but the assumption could introduce 2, 3, 5, 10 % more error into the system, that is an unknown. Take the following situation:
300w constant power 1.5% accuracy = 295-304w
300w constant power 2% accuracy = 294-306w
300w constant power 5% accuracy = 285-315w
300w constant power 7% accuracy = 279-321w
As you can see very small differences in accuracy can have a huge impact on what is still within range. Even at 1.5 % accuracy you have a potential range of +/- 4.5w now compare that to stages with potentially 5% accuracy (due to assumption) +/- 15w and you quickly realize that nothing is wrong at all.