Froome's SRM data on Ventoux

[franic]

Re: Re:

Fs isn't talking about how many tdfs riders won, but their absolute ability. If froome were doing this clean, he would be so much superior to anyone else in history. Even doped to the gills creme de la creme of the early 2000's riders like ulle couldn't go as fast as he allegedly does clean. If it were natural he would probably be the greatest athlete of all time.

I don't understand this. His peformance on Ventoux was similar to Pinot's published power outputs. How is this superior to anyone else in history?

Because otherwise it doesn't fit the narrative of posters here in The Clinic ...

Fs isn't talking about how many tdfs riders won, but their absolute ability. If froome were doing this clean, he would be so much superior to anyone else in history. Even doped to the gills creme de la creme of the early 2000's riders like ulle couldn't go as fast as he allegedly does clean. If it were natural he would probably be the greatest athlete of all time.

I don't understand this. His peformance on Ventoux was similar to Pinot's published power outputs. How is this superior to anyone else in history?

I cannot tell if you are being serious, or are that naive as to what you are comparing here or some other purpose.

As the question has already been answered at least once, it's somewhat disheartening that the questions even have to be asked.

I have seen posters suggest that actually riding a bike would help, and I would add that riding a bike with a power meter even more so.

This. One thousand times this. Too many here have never ridden a bike with some purpose, and definitely looking at their power data.

 

[Ventoux Boar]

Re: Re:

I answered the question with regard to Pinot. I mean how else could Pinot lose 6 mins to Froome when he is capable of the same power output as 'The Mutant', if he didn't have a Pinot-special headwind?

Here. Read this again:

Also, if Pinot's capabilities are to match Froome on Ventoux, that means that Pinot would have been able to finish with Froome if he had started completely fresh at the bottom of the hill, whereas Froome had to ride the 220kms beforehand, and Pinot would have paced himself up whereas Froome put in several huge attacks to drop Contador and Quintana.

On his best day, without the fatigue of a three-week stage race and without the fatigue of 220km of fast-paced racing on the flats, Pinot might have been able to follow Froome.

I understand the racing variables, cheers. I thought we dealing with the limits of human physiology, not variable form on the day? Pinot can push 6.1 for 30 mins (data from racing and training as I recall). Froome was measured at 5.7 for 45 mins. Is 5.7 w/kg in the Tour the new mutant benchmark?

 

[bewildered]

the tailwind headwind nonsense was debunked 2 years ago as I recall. There is a huge switchback on Ventoux, so a net tailwind overall only if the wind changed direction as Froome turned the switchback. mmm likely

Also Greg Henderson tweeted about a tailwind also, but he was being sarcastic - he finished 145th out of 181 finishers that day over 32 mins behind Froome.

Enough of this tailwind nonsense

 

[meat puppet]

I know that the question is 5,7w/kg the new mutant benchmark is made mockingly. However, I would be a lot more comfortable with GT racing if the climbing times converged towards the pre-EPO range of 5,5-5,8w/kg and stayed there. Feel free to mock this view. I don't mind.

That said, I came across this piece by Tucker today, which is linked below. I admit I am not an expert in these matters, but to the best of my knowledge I thought that the piece did a good job of illustrating the pickle here without reducing it to any single variable or effort (w/kg, VO2max, capacity utilization rate at FTP, efficiency). To wit, Tucker lays out what he reckons are the basic, required combinations of these variables (VO2max, capacity utilization rate at FTP, efficiency) in order to hit the 6,1w/kg for 41min that Froome did at PSM. Which I tend to think was a more incredible performance than 2013 Ventoux (discounting the fact that 220k of fast racing preceded Ventoux)

http://sportsscientists.com/2015/07/comparative-and-longitudinal-physiology/

Anyhow, I would be interested to hear what you more knowledgeable folks have to say about the piece.

 

[Alex Simmons/RST]

Re:

Via @PDXWheels on Twitter:

https://www.physicsforums.com/threa...rs-and-round-and-non-round-chainrings.774249/

Lots of interesting stuff about power meters and wonky ring shapes, consensus is that you get the same numbers, which makes sense considering foot -> pedal -> crank -> spider (all the same as round rings) and only then rings -> chain.

Oh lord, that thread! Mark has his opinions about the chainrings, but unfortunately they don't make physical or mathematical sense.

As explained ad nauseum - non circular rings by design violate the key assumption used by power meters in calculating power, that being crank rotational velocity is constant during a pedal stroke.

With circular rings that is a very good assumption (it's not exact but the error is insignificant, except under some very specific circumstances such as the initial pedal strokes of a hard acceleration).

Non circular rings by their very design introduce a sizeable crank velocity variation during a pedal stroke, which means the peak torque period is over sampled and the torque minimum period is under sampled, leading to an artificial inflation of the measured average torque, and hence artificial inflation of power numbers.

This is pretty basic power meter stuff and the effect has been measured by various people. e.g.:
http://bikeblather.blogspot.com.au/2013/01/whats-up-with-those-funky-rings.html

I'm afraid Ferrari's item doesn't address the issue of power meter accuracy, all it says is he detected no significant difference in BL or HR response between using the different rings. I'm pretty amazed he claims to have been able to climb at precisely 25W increments for 4-minutes each. At least he used a Powertap hub for power measurement, which of course is not subject the the crank velocity variation effect, only an aliasing error effect which isn't a significant concern over such durations of power measurement.

 

[The Hitch]

Re: Re:

He had a headwind? Seriously, Hitch. We have real data for Froome and Pinot. No need to be obtuse. Do we have to list some of the variables involved in racing a bike?

What the **** did I just read?

You actually buy into the magical Sky-only tailwind theory?

I answered the question with regard to Pinot. I mean how else could Pinot lose 6 mins to Froome when he is capable of the same power output as 'The Mutant', if he didn't have a Pinot-special headwind?

Pinot did ventoux the same day as froome 6 minutes slower. How can pinot have done that with the same watt output?

 

[bewildered]

because the wind changed direction immediately after Froome turned the corner. Watch his face, his expression stays the same the whole second half of the climb

 

[Alex Simmons/RST]

Re:

I know that the question is 5,7w/kg the new mutant benchmark is made mockingly. However, I would be a lot more comfortable with GT racing if the climbing times converged towards the pre-EPO range of 5,5-5,8w/kg and stayed there. Feel free to mock this view. I don't mind.

That said, I came across this piece by Tucker today, which is linked below. I admit I am not an expert in these matters, but to the best of my knowledge I thought that the piece did a good job of illustrating the pickle here without reducing it to any single variable or effort (w/kg, VO2max, capacity utilization rate at FTP, efficiency). To wit, Tucker lays out what he reckons are the basic, required combinations of these variables (VO2max, capacity utilization rate at FTP, efficiency) in order to hit the 6,1w/kg for 41min that Froome did at PSM. Which I tend to think was a more incredible performance than 2013 Ventoux (discounting the fact that 220k of fast racing preceded Ventoux)

http://sportsscientists.com/2015/07/comparative-and-longitudinal-physiology/

Anyhow, I would be interested to hear what you more knowledgeable folks have to say about the piece.

I only quickly scanned and haven't checked his numbers (it's late), but in essence it similar to what I wrote 2 years ago but without any assumptions on what is/is not plausible. Mine has charts so you can see these relationships in a graphical format.

http://alex-cycle.blogspot.com.au/2013/08/looking-under-hood.html

 

[Alex Simmons/RST]

Not sure if this was posted here already. Sky release some Froome data:
http://www.cyclingnews.com/news/team-sky-reveal-froomes-tour-de-france-data-from-stage-10/

 

[Tonton]

Re: Re:

I answered the question with regard to Pinot. I mean how else could Pinot lose 6 mins to Froome when he is capable of the same power output as 'The Mutant', if he didn't have a Pinot-special headwind?

Here. Read this again:

Also, if Pinot's capabilities are to match Froome on Ventoux, that means that Pinot would have been able to finish with Froome if he had started completely fresh at the bottom of the hill, whereas Froome had to ride the 220kms beforehand, and Pinot would have paced himself up whereas Froome put in several huge attacks to drop Contador and Quintana.

On his best day, without the fatigue of a three-week stage race and without the fatigue of 220km of fast-paced racing on the flats, Pinot might have been able to follow Froome.

Add-up: in this very thread, when I was questioning Froome's HR and % of MHR in this climb, responses from eminent contributors estimated his MHR to be in around 175 bpm based on the official low-MHR story. Now we know he clocked 178 bpm. His MHR may be 185 or so.

Now we are asked to believe that Froome's weight is 67-68kg. at 64kg, the W/kg would look quite different. 5% different

If all the numbers get distorted a little, always in his favor, then Froome's performance becomes credible.

 

[Semper Fidelis]

Re:

Hinault is the greatest of all time. Glad I could clear that up for everyone

Merckx's will headbutt-Hinault the greatest of all time!

 

[ray j willings]

The data seems to be doing it's intended job then

 

[bigcog]

Re:

The data seems to be doing it's intended job then

Quite, the silence is deafening

 

[Escarabajo]

Re: Re:

Via @PDXWheels on Twitter:

https://www.physicsforums.com/threa...rs-and-round-and-non-round-chainrings.774249/

Lots of interesting stuff about power meters and wonky ring shapes, consensus is that you get the same numbers, which makes sense considering foot -> pedal -> crank -> spider (all the same as round rings) and only then rings -> chain.

Oh lord, that thread! Mark has his opinions about the chainrings, but unfortunately they don't make physical or mathematical sense.

As explained ad nauseum - non circular rings by design violate the key assumption used by power meters in calculating power, that being crank rotational velocity is constant during a pedal stroke.

With circular rings that is a very good assumption (it's not exact but the error is insignificant, except under some very specific circumstances such as the initial pedal strokes of a hard acceleration).

Non circular rings by their very design introduce a sizeable crank velocity variation during a pedal stroke, which means the peak torque period is over sampled and the torque minimum period is under sampled, leading to an artificial inflation of the measured average torque, and hence artificial inflation of power numbers.

This is pretty basic power meter stuff and the effect has been measured by various people. e.g.:
http://bikeblather.blogspot.com.au/2013/01/whats-up-with-those-funky-rings.html

I'm afraid Ferrari's item doesn't address the issue of power meter accuracy, all it says is he detected no significant difference in BL or HR response between using the different rings. I'm pretty amazed he claims to have been able to climb at precisely 25W increments for 4-minutes each. At least he used a Powertap hub for power measurement, which of course is not subject the the crank velocity variation effect, only an aliasing error effect which isn't a significant concern over such durations of power measurement.

Thanks good readings by both.
Questions:
1- The error could be minimized by measuring speed and torque at different positions of the stroke and averaging after the stroke. I read in the forums that it requires several magnets. Do some companies do that? If they do then they don't need to count for that, correct?
2- You are using errors of 2.7% for 80 rpm. Froome uses higher rpm's than that and therefore I assume that error should be smaller at higher speed (more homogeneous Torquing). Why is Brailsford using 6% correction factor?

Still don't understand with todays tools and technology that average speed for these elliptical rings cannot be measured over a crank spin. And the need to correct for that???

Thanks.

 

[Escarabajo]

Re: Re:

He had a headwind? Seriously, Hitch. We have real data for Froome and Pinot. No need to be obtuse. Do we have to list some of the variables involved in racing a bike?

What the **** did I just read?

You actually buy into the magical Sky-only tailwind theory?

I answered the question with regard to Pinot. I mean how else could Pinot lose 6 mins to Froome when he is capable of the same power output as 'The Mutant', if he didn't have a Pinot-special headwind?

Pinot did ventoux the same day as froome 6 minutes slower. How can pinot have done that with the same watt output?

He is using the maximum number done by pinot (different time I guess) ignoring conditions (wind, length, day of the race) and comparing it against Froome that day. I my opinion he is basically trolling. He knows he/she is doing something wrong.

 

[ScienceIsCool]

Re: Re:

Via @PDXWheels on Twitter:

https://www.physicsforums.com/threa...rs-and-round-and-non-round-chainrings.774249/

Lots of interesting stuff about power meters and wonky ring shapes, consensus is that you get the same numbers, which makes sense considering foot -> pedal -> crank -> spider (all the same as round rings) and only then rings -> chain.

Oh lord, that thread! Mark has his opinions about the chainrings, but unfortunately they don't make physical or mathematical sense.

As explained ad nauseum - non circular rings by design violate the key assumption used by power meters in calculating power, that being crank rotational velocity is constant during a pedal stroke.

With circular rings that is a very good assumption (it's not exact but the error is insignificant, except under some very specific circumstances such as the initial pedal strokes of a hard acceleration).

Non circular rings by their very design introduce a sizeable crank velocity variation during a pedal stroke, which means the peak torque period is over sampled and the torque minimum period is under sampled, leading to an artificial inflation of the measured average torque, and hence artificial inflation of power numbers.

This is pretty basic power meter stuff and the effect has been measured by various people. e.g.:
http://bikeblather.blogspot.com.au/2013/01/whats-up-with-those-funky-rings.html

I'm afraid Ferrari's item doesn't address the issue of power meter accuracy, all it says is he detected no significant difference in BL or HR response between using the different rings. I'm pretty amazed he claims to have been able to climb at precisely 25W increments for 4-minutes each. At least he used a Powertap hub for power measurement, which of course is not subject the the crank velocity variation effect, only an aliasing error effect which isn't a significant concern over such durations of power measurement.

Thanks good readings by both.
Questions:
1- The error could be minimized by measuring speed and torque at different positions of the stroke and averaging after the stroke. I read in the forums that it requires several magnets. Do some companies do that? If they do then they don't need to count for that, correct?
2- You are using errors of 2.7% for 80 rpm. Froome uses higher rpm's than that and therefore I assume that error should be smaller at higher speed (more homogeneous Torquing). Why is Brailsford using 6% correction factor?

Still don't understand with todays tools and technology that average speed for these elliptical rings cannot be measured over a crank spin. And the need to correct for that???

Thanks.

The problem is that you need to know the instantaneous speed and not the average speed because P = T x w. Power equals torque times velocity (cadence). Taking average torque times average speed is very, very different from taking 100 measurements per revolution and adding them up. This is the primary source of error. Also using magnets is awful too. Do you count the revolution at the rising edge of the signal? Trailing edge? What happens if you get "ringing"? Awful. The best way to do it would be with an optical encoder on the crank spindle.

John Swanson

 

[MTBrider]

Pretty funny to see people who have obviously never used a power meter or perhaps even trained trying to analyze power files.

The 5.7 watts/kg is what Froome's PM measured on that day. He could have ridden with an SRM and had it measure 5.9 watts/kg or a power tap and have it measure 5.5 watts/kg. There are huge variations between power meters, particularly when there is temperature variation. You have to remember power meters are primarily training tools, as a training tool the actual number isn't that important, but consistent measurement is important.

You also have to understand effect of weather on power outputs. For Froome to produce 5.7 watts/kg in super hot conditions is very impressive. The number would have been a lot higher if it was cooler.

Even then, in the grand scheme of things 6.0 watts/kg isn't as usual as it sounds. There are many regional level pros who in training can do 6.0 for 30 minutes. Of course doing it at the end of 150km stage after 10 days of racing is entirely different.

 

[Ventoux Boar]

Re: Re:

He had a headwind? Seriously, Hitch. We have real data for Froome and Pinot. No need to be obtuse. Do we have to list some of the variables involved in racing a bike?

What the **** did I just read?

You actually buy into the magical Sky-only tailwind theory?

I answered the question with regard to Pinot. I mean how else could Pinot lose 6 mins to Froome when he is capable of the same power output as 'The Mutant', if he didn't have a Pinot-special headwind?

Pinot did ventoux the same day as froome 6 minutes slower. How can pinot have done that with the same watt output?

He is using the maximum number done by pinot (different time I guess) ignoring conditions (wind, length, day of the race) and comparing it against Froome that day. I my opinion he is basically trolling. He knows he/she is doing something wrong.

Eh? I'm only asking why Froome was mutant on Ventoux 2013, and Pinot wasn't on Hautacam 2014 when their power outputs were comparable (if you believe the data). The data was posted above. That should be an incredibly straightforward question to answer.

 

[gazr99]

Re: Re:

[quote="

Eh? I'm only asking why Froome was mutant on Ventoux 2013, and Pinot wasn't on Hautacam 2014 when their power outputs were comparable (if you believe the data). The data was posted above. That should be an incredibly straightforward question to answer.

Froome rides for Sky, Pinot doesn't

 

[Netserk]

Re: Re:

Eh? I'm only asking why Froome was mutant on Ventoux 2013, and Pinot wasn't on Hautacam 2014 when their power outputs were comparable (if you believe the data). The data was posted above. That should be an incredibly straightforward question to answer.

What was the length of the efforts and at what altitudes?

 

[hfer07]

If SKY states it - then it must be LEGIT

We should be asking for Porte's & Quintanita's SMR data to see what they produced and therefore scale proportionally the efforts

 

[Escarabajo]

Re: Re:

Via @PDXWheels on Twitter:

https://www.physicsforums.com/threa...rs-and-round-and-non-round-chainrings.774249/

Lots of interesting stuff about power meters and wonky ring shapes, consensus is that you get the same numbers, which makes sense considering foot -> pedal -> crank -> spider (all the same as round rings) and only then rings -> chain.

Oh lord, that thread! Mark has his opinions about the chainrings, but unfortunately they don't make physical or mathematical sense.

As explained ad nauseum - non circular rings by design violate the key assumption used by power meters in calculating power, that being crank rotational velocity is constant during a pedal stroke.

With circular rings that is a very good assumption (it's not exact but the error is insignificant, except under some very specific circumstances such as the initial pedal strokes of a hard acceleration).

Non circular rings by their very design introduce a sizeable crank velocity variation during a pedal stroke, which means the peak torque period is over sampled and the torque minimum period is under sampled, leading to an artificial inflation of the measured average torque, and hence artificial inflation of power numbers.

This is pretty basic power meter stuff and the effect has been measured by various people. e.g.:
http://bikeblather.blogspot.com.au/2013/01/whats-up-with-those-funky-rings.html

I'm afraid Ferrari's item doesn't address the issue of power meter accuracy, all it says is he detected no significant difference in BL or HR response between using the different rings. I'm pretty amazed he claims to have been able to climb at precisely 25W increments for 4-minutes each. At least he used a Powertap hub for power measurement, which of course is not subject the the crank velocity variation effect, only an aliasing error effect which isn't a significant concern over such durations of power measurement.

Thanks good readings by both.
Questions:
1- The error could be minimized by measuring speed and torque at different positions of the stroke and averaging after the stroke. I read in the forums that it requires several magnets. Do some companies do that? If they do then they don't need to count for that, correct?
2- You are using errors of 2.7% for 80 rpm. Froome uses higher rpm's than that and therefore I assume that error should be smaller at higher speed (more homogeneous Torquing). Why is Brailsford using 6% correction factor?

Still don't understand with todays tools and technology that average speed for these elliptical rings cannot be measured over a crank spin. And the need to correct for that???

Thanks.

The problem is that you need to know the instantaneous speed and not the average speed because P = T x w. Power equals torque times velocity (cadence). Taking average torque times average speed is very, very different from taking 100 measurements per revolution and adding them up. This is the primary source of error. Also using magnets is awful too. Do you count the revolution at the rising edge of the signal? Trailing edge? What happens if you get "ringing"? Awful. The best way to do it would be with an optical encoder on the crank spindle.

John Swanson

Thanks for the answer.

To the bolded. Is that possible with power meters today? do some power meter have this capability?
The integration of the Torque times the angular velocity is what gives me power which equivalent to the summation. In that case we would not need a correction factor if well calibrated, right?

 

[Escarabajo]

Re:

Pretty funny to see people who have obviously never used a power meter or perhaps even trained trying to analyze power files.

The 5.7 watts/kg is what Froome's PM measured on that day. He could have ridden with an SRM and had it measure 5.9 watts/kg or a power tap and have it measure 5.5 watts/kg. There are huge variations between power meters, particularly when there is temperature variation. You have to remember power meters are primarily training tools, as a training tool the actual number isn't that important, but consistent measurement is important.

You also have to understand effect of weather on power outputs. For Froome to produce 5.7 watts/kg in super hot conditions is very impressive. The number would have been a lot higher if it was cooler.

Even then, in the grand scheme of things 6.0 watts/kg isn't as usual as it sounds. There are many regional level pros who in training can do 6.0 for 30 minutes. Of course doing it at the end of 150km stage after 10 days of racing is entirely different.

I have not used a power meter in my life. Just in the labs when I went to school of engineering.
Don't know about you but 6 watts/ kg seems very high to me. Maybe not in 30 minutes but in 40+ minutes is very high.

So in comparing the numbers is valuable qualitatively, in that case we need the complete set of data for other days with the same calibration. Otherwise why measure it. I would think it would have some value quantitatively as well. What is the point of measuring it? Especially for these pros. I understand why it would be more important for me to compare my performance from one day to another with an uncalibrated power meter or different brands (who cares), but for these guys it is paramount to have tweaked to the millimeter. Otherwise they would not know whether they are gaining an advantage or not against the opposition.

Don't need to patronize me. Thanks.

 

[Merckx index]

Re:

Even then, in the grand scheme of things 6.0 watts/kg isn't as usual as it sounds. There are many regional level pros who in training can do 6.0 for 30 minutes. Of course doing it at the end of 150km stage after 10 days of racing is entirely different.

There was a guy here a couple of years ago who claimed he could do 6.27 W/kg for I think 30 minutes. I have trouble believing this story. In Tucker’s latest blog, he points out that Pinot does 6.1 W/kg for 30 minutes. Not at the end of a long stage, this is basically his top value when he measures it on the road in a training exercise.

He has a V02max of 85, so assuming an efficiency of 23%, he can put out 89% of that for 30 minutes. That is very exceptional, yet we’re supposed to believe lots of regional pros can about match it?

Have these pros published their V02max values? Unless they are well over 80, or unless they have exceptionally high efficiencies (which are disputed by some researchers), 6.0 W/kg for 30 min. really isn’t very believable. As I pointed out upthread, most elite riders who have been studied have V02max values and efficiencies that indicate they can’t put out this much power for slightly longer periods of time.

 

[ScienceIsCool]

Re: Re:

Thanks for the answer.

To the bolded. Is that possible with power meters today? do some power meter have this capability?
The integration of the Torque times the angular velocity is what gives me power which equivalent to the summation. In that case we would not need a correction factor if well calibrated, right?

To the best of my knowledge, no power meter on the market samples angular velocity more than once or twice per revolution - so no integration and therefore some inaccuracy. To add an encoder would definitely add cost, weight, complexity as well as demand more computing resources which is probably why nobody does it. As it is right now, it can be a bit of an effort to stuff a device full of strain gauges and get meaningful data. Then you have to deal with things like vibration, temperature drift, calibration, etc, etc. Oh, and try to get the cost down to a couple hundred bucks so you can make a living at it.

Of course, this doesn't mean current power meters are useless even if they are inaccurate. Taking large time-based samples allows you to average out the data and get a pretty good picture of performance - which is why Froome *really* hates that the Ventoux data got out into the wild. Talk inaccuracies and 6% errors all you want, there's more than enough data to get a good picture of how well he's riding. And when you back that up with different methods (a la Vayer, Ferrari et al) you can have a lot of confidence in your conclusions.

Which is why Sky's "release of data" is just so much bullsh!t. Instead of feeding us the conclusions, hand over the raw data. It'll pretty much confirm that he did 6.1+ W/kg so we'll never see it.

John Swanson