I have never used a power meter but I read somewhere that they are to be approached in the same way as say bathroom scales i.e. that you use the same scales to weigh yourself each week to get an accurate idea of where you are. The theory being that most sets of scales have a variable of +/- a certain %.
If you had been measuring your weight for a year using the same scales then jumped on another set it would give you a misleading weight. The same could be said of weighing yourself first thing in the morning as against last thing at night after a 3 course meal.
I am not physiologist but I guess the same logic would apply to most statistics including power.
If you had been measuring your weight for a year using the same scales then jumped on another set it would give you a misleading weight. The same could be said of weighing yourself first thing in the morning as against last thing at night after a 3 course meal.
I am not physiologist but I guess the same logic would apply to most statistics including power.
- Mar 10, 2009
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So it turns out that Froome's power measurement was from a left side only Stages with O-sym rings. Hardly a reliable data point.
http://www.cyclingnews.com/news/chris-froomes-tour-de-france-winning-pinarello-dogma-f8/
http://www.cyclingnews.com/news/chris-froomes-tour-de-france-winning-pinarello-dogma-f8/
- Aug 12, 2009
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any thoughts on the 1.5% accounted for by the new 'aggressive' chainrings?
otherwise chimes with what you've been saying re: 4.5%-5%
Alex Simmons/RST said:
any thoughts on the 1.5% accounted for by the new 'aggressive' chainrings?
otherwise chimes with what you've been saying re: 4.5%-5%
- Mar 10, 2009
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But as I also explain, the error isn't a consistent one, it also varies with the type of riding and I would expect, for instance, it to be larger error when climbing than on flatter terrain.
Layer on top the left crank only measurement, and that power output asymmetry is naturally variable. e.g. a modest 2% asymmetry means a 4% error in power. And that assumes the unit is accurately measuring left crank power to start with. End result is no one can ever know what the error of that power file is. It's both unknown and variable.
There's no doubt the level of eccentricity will impact power measurement error. I can't really comment on how different the rings are as I don't know.gillan1969 said:
But as I also explain, the error isn't a consistent one, it also varies with the type of riding and I would expect, for instance, it to be larger error when climbing than on flatter terrain.
Layer on top the left crank only measurement, and that power output asymmetry is naturally variable. e.g. a modest 2% asymmetry means a 4% error in power. And that assumes the unit is accurately measuring left crank power to start with. End result is no one can ever know what the error of that power file is. It's both unknown and variable.
- Jul 13, 2011
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Alex: thanks for keeping everyone in order regarding the power data, there is a lot of misinformation and people not wanting to understand the numbers and reasons behind them.
I ride with a left only crank based powermeter, I am aware that it is not perfect, but for what I need it for, it is much better than nothing. My question is why are Sky using an budget product AND coupling that to an Osymetric crank, when they are all about the numbers? Froome stares at his stem the whole time, it seems weird that they accept a larger than neccessary variation. I know they are sponsored by Stages, but they could have an SRM too and normal cranks.
I wonder if in the future cycling will have a weigh in and power numbers on TV. I think that would be great, not so much for doping talk, just for viewing.
I ride with a left only crank based powermeter, I am aware that it is not perfect, but for what I need it for, it is much better than nothing. My question is why are Sky using an budget product AND coupling that to an Osymetric crank, when they are all about the numbers? Froome stares at his stem the whole time, it seems weird that they accept a larger than neccessary variation. I know they are sponsored by Stages, but they could have an SRM too and normal cranks.
I wonder if in the future cycling will have a weigh in and power numbers on TV. I think that would be great, not so much for doping talk, just for viewing.
- Sep 29, 2012
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So cool that despite the alleged inaccuracy, the data crunchers continue to predict average power up climbs to within 1%.
Skillz, yo.
Skillz, yo.
Yep. Skillz.
- Apr 20, 2012
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Sarcasm is great.
Yeah, how odd is it the data boys are always incorrect on just one particular Sky rider? THey must have an agenda. Especially the guy from Finland has an agenda, always about 1% off and but not on Froome. Data bender that guy, he must really hate Sky.Dear Wiggo said:
Sarcasm is great.
- Sep 29, 2012
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Agreed. My doctor prescribes a minimum sarcasm dosage of 2 posts bd.
Fearless Greg Lemond said:
Agreed. My doctor prescribes a minimum sarcasm dosage of 2 posts bd.
- Jul 7, 2013
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Can someone explain to me that considering all the power meters in the peloton seem to be pretty inaccurate what do riders gain from having them on their bikes and riding to certain (non accurate) wattages?
Alex Simmons/RST said:
Can someone explain to me that considering all the power meters in the peloton seem to be pretty inaccurate what do riders gain from having them on their bikes and riding to certain (non accurate) wattages?
- Sep 29, 2012
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Repeatability tends to be good, allowing for tracking of progress / improvement.
I find the quibbling about accuracy to be misguided in terms of what is being discussed.
I don't need to see a power file from Froome to know he is doping as full *** as possible.
AICA ribonucleotide said:
Repeatability tends to be good, allowing for tracking of progress / improvement.
I find the quibbling about accuracy to be misguided in terms of what is being discussed.
I don't need to see a power file from Froome to know he is doping as full *** as possible.
Here we go, meeelion dollar question.NUFCrichard said:
But... Brailsford has everything calculated to the last 0.01%, so either they are somehow fooling Vroom himself, or the whole leak is part of the game - the more versions you manage to launch to the public, the less probable/believable each one gets, including the ones against you. Nothing new, just some good old infowar methods, confusion, doubts, no truth nowhere.
- Sep 29, 2012
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What I don't understand is with error should be biased towards reducing Froome's power data. Given what we know, the safest bet is probably to assume it is symmetric and the data we have is unbiased, especially if you consider that is pretty close to what it has been estimated from climbing times.Alex Simmons/RST said:
- Mar 10, 2009
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Some will be, some have very limited validation of their performance since they are so new (and early testing shows up such issues) while others are not inherently inaccurate if used correctly but there can be user error.
But if using power data (for whatever reason) then it makes sense to at least validate the quality of the data in context of the use one is making of it. e.g. if you are using a power meter data point to compare to a modelled estimate of climbing power, then one should validate the quality of the data.
As to those who choose to use equipment that has an inherent accuracy flaw(s), you'd have to ask them. IMO use of inaccurate power meters invalids a large number of valuable strategic insights and uses for having such data, and I don't see the point of them.
As for riding to a power number or range, while that may be common for lots of people, it's probably the lowest fi and most limited tactical use of a power meter. When used in this tactical manner, other than for specific pacing guidance, e.g. the opening minutes of a TT when it's soooo easy to go too hard, or say guiding the initial minute of VO2max work, the use of power for guiding intensity isn't overly demanding on accuracy. So non-demanding that one can train just about as effectively using perceived exertion and a watch (while gathering accurate power data for more useful purposes).
One can make up for such data deficiencies in other ways, e.g. having a long prior data history with quality measurement, close personal monitoring, wind tunnels, using better equipment for performance testing or in training and so on, so it'll depend on resources and context.
An accurate meter's biggest value is in other areas of performance assessment, review and management. It's much more a strategic tool than a tactical one but it's the tactical use that many seem overly obsessed with or caught up on.
I wouldn't say they are all inaccurate.AICA ribonucleotide said:
Some will be, some have very limited validation of their performance since they are so new (and early testing shows up such issues) while others are not inherently inaccurate if used correctly but there can be user error.
But if using power data (for whatever reason) then it makes sense to at least validate the quality of the data in context of the use one is making of it. e.g. if you are using a power meter data point to compare to a modelled estimate of climbing power, then one should validate the quality of the data.
As to those who choose to use equipment that has an inherent accuracy flaw(s), you'd have to ask them. IMO use of inaccurate power meters invalids a large number of valuable strategic insights and uses for having such data, and I don't see the point of them.
As for riding to a power number or range, while that may be common for lots of people, it's probably the lowest fi and most limited tactical use of a power meter. When used in this tactical manner, other than for specific pacing guidance, e.g. the opening minutes of a TT when it's soooo easy to go too hard, or say guiding the initial minute of VO2max work, the use of power for guiding intensity isn't overly demanding on accuracy. So non-demanding that one can train just about as effectively using perceived exertion and a watch (while gathering accurate power data for more useful purposes).
One can make up for such data deficiencies in other ways, e.g. having a long prior data history with quality measurement, close personal monitoring, wind tunnels, using better equipment for performance testing or in training and so on, so it'll depend on resources and context.
An accurate meter's biggest value is in other areas of performance assessment, review and management. It's much more a strategic tool than a tactical one but it's the tactical use that many seem overly obsessed with or caught up on.
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Well there are factors that will bias the O-sym/Stages data in one direction and which are well established. But there are other errors that may in fact go the other direction (e.g. the asymmetry error, or slope error, or offset error) but are unknowns and so we cannot say with any certainty.
I've only pointed out the source of errors and what effect they have on recorded data. Some will artificially inflate it, others may deflate it, while others are unknown or in some cases, unknowable.
Have they?franic said:
Well there are factors that will bias the O-sym/Stages data in one direction and which are well established. But there are other errors that may in fact go the other direction (e.g. the asymmetry error, or slope error, or offset error) but are unknowns and so we cannot say with any certainty.
I've only pointed out the source of errors and what effect they have on recorded data. Some will artificially inflate it, others may deflate it, while others are unknown or in some cases, unknowable.
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In your case you don't need power data to determine a rider's doping status. Which I suppose begs the question, why do people think having power data is so important in the context of deciding on a rider's doping status when it's clearly not necessary for you?
There is a legitimate difference between discussing the quality of power data, whether it be via modelled estimates or measuring equipment, and discussing what one can or cannot infer from such data.Dear Wiggo said:
In your case you don't need power data to determine a rider's doping status. Which I suppose begs the question, why do people think having power data is so important in the context of deciding on a rider's doping status when it's clearly not necessary for you?
- Apr 20, 2012
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What are the odds on having wattages calculations wrong on just one rider due to osym-rings, this while a lot - a real lot - of other calculations where within 1% of discrepancy? Does O-sym rings break some sort of standard deviation rule?
Odds?
Or just odd?
Question:Alex Simmons/RST said:
What are the odds on having wattages calculations wrong on just one rider due to osym-rings, this while a lot - a real lot - of other calculations where within 1% of discrepancy? Does O-sym rings break some sort of standard deviation rule?
Odds?
Or just odd?
- Sep 29, 2012
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Most likely because those people are not me.
I thought that would have been obvious.
Alex Simmons/RST said:
Most likely because those people are not me.
I thought that would have been obvious.
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Osyms artificially inflate power readings, that's well known.
It is a specific bias error that operates in one direction only (but is a somewhat variable error).
But if there are other forms of bias or semi-random error that, e.g. may cause power to be under reported, then it's feasible that these errors are in part cancelling each other out.
As I've said, there are a range of error factors. Some we know will bias data in one direction. Others we don't know and can't know.
How do people know the actual power to within 1%? If by that they mean a model power estimate of a different rider compared with the data from the same rider's unverified power meter, then I'd be a little more cautious than to claim such a level of individual accuracy with my model or to think my estimate was robust.
When such models have been put through more scientific rigour to assess their validity, they demonstrate two results:
- on average their accuracy is pretty good
- however they have a sizeable error range for individual data points, so it's not a particularly precise method (+/- 6%, and +/- 10% when windy)
I not sure I understand what you are saying.Fearless Greg Lemond said:
Osyms artificially inflate power readings, that's well known.
It is a specific bias error that operates in one direction only (but is a somewhat variable error).
But if there are other forms of bias or semi-random error that, e.g. may cause power to be under reported, then it's feasible that these errors are in part cancelling each other out.
As I've said, there are a range of error factors. Some we know will bias data in one direction. Others we don't know and can't know.
How do people know the actual power to within 1%? If by that they mean a model power estimate of a different rider compared with the data from the same rider's unverified power meter, then I'd be a little more cautious than to claim such a level of individual accuracy with my model or to think my estimate was robust.
When such models have been put through more scientific rigour to assess their validity, they demonstrate two results:
- on average their accuracy is pretty good
- however they have a sizeable error range for individual data points, so it's not a particularly precise method (+/- 6%, and +/- 10% when windy)
- Oct 4, 2014
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On the other hand I’m not fully convinced by the test they did. IMHO, we should expect power measured at the wheel using an indoor trainer to be smaller than power measured at the pedal with SRM/Stage.
I was referring to left/right imbalance with Stages.Alex Simmons/RST said:
On the other hand I’m not fully convinced by the test they did. IMHO, we should expect power measured at the wheel using an indoor trainer to be smaller than power measured at the pedal with SRM/Stage.
- Aug 15, 2012
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Not to oversimplify, but I always thought power to bottom bracket was just that. I'm admittedly unfamiliar with stages, but power applied should be static and easily calculated. Then again I still run biopace on my old teesdale...
Edited for new phone gremlins.
Edited for new phone gremlins.
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