I use both single and double sided meters and find little/no benefit to double sided. Contrary to what others have stated, I rarely, if ever, see any variance in R/L power. Seems to always be 49/50. Maybe, I am an outlier?
“If the device receives all the relevant data (i.e. data from both the right and left leg), then it’s a power meter.”
No, most definitely not. See iBike (or whatever they call it now).
Not sure I follow. The iBike is inarguably a power estimator, as it doesn’t even purport to measure power, as it does not measure torque or cadence. Instead, it estimates power based on non-power data (speed, wind, gradient, etc).
Not sure I follow. The iBike is inarguably a power estimator, as it doesn’t even purport to measure power, as it does not measure torque or cadence. Instead, it estimates power based on non-power data (speed, wind, gradient, etc).
I think you’re intending to use “estimator” with the idea of using the dictionary definition of “estimate” as a pejorative - something like “rough guess.”
But in engineering terms an “estimator” is not a pejorative. It’s just something that takes observed data, each with some error, the produces an inferred value for a model parameter. In the case of power meters the observed data are things like temperature, angular rate, and material deflection. Each of those has some error, angular rates are sampled over a pedal stroke, temperature readings have errors, strain gages can have calibration issues, etc. That error gets propagated to the inferred model value - human power output. Single leg power meters have less observed data and more un-modeled dynamics - the contribution of the un-observed leg.
So go ahead and call the single-leg power meter possibly less accurate, subject to error conditions better handled by other types of power meters.
But I’ll continue to cringe at it being called an “estimator.”
If you find one side is significantly putting out more power what would you do?
The issue isn’t with whether the data is actionable, it’s whether it’s accurate or more importantly consistent. If your L:R balance was consistently 45:55, then a one-sided PM would be inaccurate but consistent. 300W might actually be 270W or 330W on a different PM, but at least 300W one day is the same as 300W the next day, so the data is usable - you can set target power and perform tests with it.
Problem is that in my experience L:R balance isn’t consistent. Mine varies from 45:55 to 51:49. There is some correlation with intensity and fatigue, but I only know that because I can measure it. If I had a single sided PM then the same effort might show as 300W or might show as 265W depending on whether I was having a 45:55 day or a 51:49 day.
I don’t care that much that on some days I have a 45:55 L:R balance (that’s not quite true, I’m doing some single leg exercises to see if I can get it closer to 50:50 more of the time, but it’s within normal range and nothing to really worry about) but a >10% variance in recorded power would basically render a PM worse than useless. I’d have no issue buying something like a hub-based PM which measures total power without distinguishing between L and R. But no way would I consider a single-sided one.
This is exactly my experience as well. Having been able to measure and monitor L/R balance for several years now, I know that it varies day by day and within a workout based on intensity and fatigue. Knowing what I know now about my L/R balance throughout a workout and day to day, I would never trust that a single-sided PM could produce accurate and repeatable power measurements for me. Others may be different, but would you really know without first riding for years with a power meter that measures L/R balance? No.
x3. I’ve seen my L/R balance vary from 47/53 to 52/48 at any given time. It’s not consistent nor predictable within a ride, across different efforts, or day to day. Hence while the overall average power may be within the ball park, at any given moment it could be way out of whack and no better than RPE or HR. Knowing in the back of my head that it’s plausible that my L/R balance is impacting the power numbers on my computer is just something not worth dealing with and I rather spend more money on a PM that reads total power.
The whole purpose of a PM, at least in my opinion, is to remove doubt on how hard you’re working. So why invest any money in a PM that brings doubt into the picture? If others are okay with that…by all means go for it. But it would drive me nuts.