Xplora wrote:jcjordan wrote:I would like to see some more user reviews before I would consider stages.
The need to double the readings from one crank just seems to add to much of a error factor for my liking.
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This completely misunderstands the reasoning behind training with power - unless your interest is showing off, then the main criteria is consistency and repeatability. It doesn't matter if your 100W reads as 200W, a training program revolves around TSS and FTP - which are effectively just maths around a couple constants. You don't need to know what the exact figures are. You need to know that you can put out Xwatts for Yseconds Ztimes in the race or the week.
There are many applications of power meters and their data, and some of those applications require greater precision than others, so first up one needs to understand for what purposes you intend to use the meter and the data.
Stages might be fine for some of the least demanding applications of power meter data but it will be inadequate for other uses. The data from Stages may be suitable for many and present a good option, although it's early days yet on the longevity/reliability front.
Xplora wrote:It doesn't make a difference if you are getting this from one leg or two - UNLESS you specifically require measurement of both legs, in which case most power meters can't do that anyway!
The total power output of both legs very much does matter from a performance perspective and again it depends on what you need the data for. Stages make a fairly large assumption that total power = 2 x left leg power, always. This simply isn't the case, and the difference varies with duration, relative power level, cadence and fatigue levels, let alone from person to person.
I'm a lower left leg amputee. Do you reckon it would be accurate for me? I also know my left-right contribution changes significantly depending on various factors.
All other power meters measure the combined power of both legs. Some attempt to provide a left-right split, although one has to define what is meant by left and right power, indeed isolating such things is actually pretty hard to do (keep in mind the cranks are connected system). I do agree that L-R information is of limited value and provides little if any actionable intelligence. Total power output is what matters.
Xplora wrote:You aren't getting error from multiplying the legs. You get error from a bad measurement. Stages seems to be OK at measurement.
Yes, Stages may well be measuring the left crank well, however you are most definitely getting an error from multiplying that by 2 and assuming that represents total power output. It's an error that we cannot quantify nor know how it varies for any individual without lab based testing with special equipment only available to a handful of labs, and even then it may be different in the field.
What one then has to determine is whether that level of uncertainty about this unknown error matters for the purpose to which you wish to use the meter (it's a "known unknown" in Rumsfeld speak).
Xplora wrote:They charge what they charge. I am not surprised. People won't buy a cheap PM. "Toy" is the label. Look at the PowerCal. Too cheap to be taken seriously.
The PowerCal is not taken seriously as a power meter because it is not a power meter.