So I am in a dreaming moment and looking at power meters, a long way from getting one, but had a question about the differences between the Hub based and the Crank based, everything I am reading states that Crank based is about the same accuracy wise but will read a higher number (which is fine).
My question though lies in that I currently run Osymetric chain rings (yes some people think they don’t actually work, and maybe they don’t, but I think they do and like the way that they work for me), but will the Osymetric rings affect the readings I get from a crank power meter?
This may be a total newbie question when it comes to power meters, and I am sorry about that but I am just doing initial research into power meters, so still am new to them, so please be gentle but any help will be greatly appreciated.
So I am in a dreaming moment and looking at power meters, a long way from getting one, but had a question about the differences between the Hub based and the Crank based, everything I am reading states that Crank based is about the same accuracy wise but will read a higher number (which is fine).
**My question though lies in that I currently run Osymetric chain rings (yes some people think they don’t actually work, and maybe they don’t, but I think they do and like the way that they work for me), but will the Osymetric rings affect the readings I get from a crank power meter? **
This may be a total newbie question when it comes to power meters, and I am sorry about that but I am just doing initial research into power meters, so still am new to them, so please be gentle but any help will be greatly appreciated.
Yes it will affect the readings but assuming you only have one bike, or you have the same chainrings on all your bikes it won’t matter if you have crank based power on all your bikes.
So I am in a dreaming moment and looking at power meters, a long way from getting one, but had a question about the differences between the Hub based and the Crank based, everything I am reading states that Crank based is about the same accuracy wise but will read a higher number (which is fine).
**My question though lies in that I currently run Osymetric chain rings (yes some people think they don’t actually work, and maybe they don’t, but I think they do and like the way that they work for me), but will the Osymetric rings affect the readings I get from a crank power meter? **
This may be a total newbie question when it comes to power meters, and I am sorry about that but I am just doing initial research into power meters, so still am new to them, so please be gentle but any help will be greatly appreciated.
Yes it will affect the readings but assuming you only have one bike, or you have the same chainrings on all your bikes it won’t matter if you have crank based power on all your bikes.
Im just kinda wondering about whether or not I should go to crank based or hub based, I did buy a Boyd wheel a little bit ago and didn’t opt for the power meter so I would have to either get that real laced with a hub based meter or go with crank based power (and that being said I only have the one bike), so I am leaning towards the crank based
So I am in a dreaming moment and looking at power meters, a long way from getting one, but had a question about the differences between the Hub based and the Crank based, everything I am reading states that Crank based is about the same accuracy wise but will read a higher number (which is fine).
**My question though lies in that I currently run Osymetric chain rings (yes some people think they don’t actually work, and maybe they don’t, but I think they do and like the way that they work for me), but will the Osymetric rings affect the readings I get from a crank power meter? **
This may be a total newbie question when it comes to power meters, and I am sorry about that but I am just doing initial research into power meters, so still am new to them, so please be gentle but any help will be greatly appreciated.
Yes it will affect the readings but assuming you only have one bike, or you have the same chainrings on all your bikes it won’t matter if you have crank based power on all your bikes.
The amount of error in power measurement introduced by non-circular rings depends on the nature of riding being done - crank velocity variance is not a constant but itself varies. e.g. the error in power caused would likely not be the same on flat terrain as on steeper hills.
Rotor also just released a new power meter that goes into the spindle and has software which adjusts for the oval chainrings. That being said it’s for BB30 (or any 30mm spindle) crankset.
If you are wondering who to believe, believe Andrew Coggan not me!!
As people should, since I’m apparently the first person to ever recognize the issue.
SRM will work with rotor rings if SRM calibrates it. I have ridden mine with a power tap and a computrainer. Yes, I am that much of a geek.
Given your basis for comparison, I am not surprised that you haven’t been able to detect any difference.
Nonetheless, the use of non-round rings combined with the assumption of a constant crank angular velocity by SRM (and others! I.e., it isn’t unique to SRM) results in a small and variable overestimation of true power.
I use Rotor’s power meter which they claim has 500hz sampling rate, along with Q-rings. I don’t know if their sampling rate includes at least an approximation for instantaneous angular velocity, but they explicitly support Q-rings. Although I read about these issues before I made my power meter purchase, it baffles me that any power meter wouldn’t sample angular velocity and load often enough to be ring-eccentricity agnostic.
I use Rotor’s power meter which they claim has 500hz sampling rate, along with Q-rings. I don’t know if their sampling rate includes at least an approximation for instantaneous angular velocity, but they explicitly support Q-rings. Although I read about these issues before I made my power meter purchase, it baffles me that any power meter wouldn’t sample angular velocity and load often enough to be ring-eccentricity agnostic.
Best anyone has been able to determine, they simply use the accelerometers to determine how long it takes to complete one full revolution, not the near-instantaneous angular velocity. That’s probably a good thing, actually, due to the difficulty in separating the true signal from the noise caused, e.g., by bumps in the road. (A problem they had had initially, until a firmware update solved it, presumably by applying even heavier damping.)
To be honest, when it comes to calculating power I really don’t understand the fascination with use of accelerometers instead of a simple reed switch to determine angular velocity. Sure, it means you may not have to have a magnet attached to your bike, but the limitations don’t seem to outweigh that benefit.
I can believe it’s a compromise based on how noisy the calculation will be, since the error would have to be less than that which you are trying to correct. Still, I would think 500hz would be more than enough to apply some Kalman filtering to and get decent results :).
An issue with positional sensors is that you’d have to take a discrete derivative to get angular velocity, perhaps second order with additional damping/smoothing… whereas with an inertial sensor you can just use a_c=omega^2*r_sensor → omega=sqrt(a_c/r_sensor) (This is what I’ve assumed Rotor was doing), as you mention, with some type of smoothing. To give developers some credit, It’s always easier to assume a problem is trivial until you try it yourself, and I haven’t tried to make my own power meter.
What about the options of pedal based power meters? Would they be more accurate for my setup?
Just trying to get an idea how this stuff all works, and this is def. too technical for me to understand and I don’t wanna spend that kind of money and not get a good option