- Sep 29, 2012
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Krebs cycle said:lol someone doesn't know the difference between joules and calories
Fail.
I am sure if you ask around, someone can explain it to you.
Krebs cycle said:lol someone doesn't know the difference between joules and calories
Fail.
biker jk said:Ten Dam said there was a headwind, as did the commentators (Phil and Paul). I suggest we add 0.5W/kg to the estimates.
Alex Simmons/RST said:I suggest noting what I wrote.
Alex Simmons/RST said:Greg Henderson tweeted he had a strong tailwind for the climb.
Assuming that's the case, I suggest dropping estimated W/kg numbers by at least 0.5W/kg, if not more.
Alex Simmons/RST said:Phil and Paul can't even get the rider's names right, let alone what the wind is doing. Only time I heard them talk about the wind was in reference to the final hundred metres.
The fact that we have such varied reports simply means that such estimates will have quite large errors in their calculation.
I looked back on video of the Armstrong/Pantani Ventoux ascent, and it seemed to be quite strong headwind for large sections, could be easily a 1W/kg difference for same time depending on the wind.
biker jk said:Ten Dam said there was a headwind, as did the commentators (Phil and Paul). I suggest we add 0.5W/kg to the estimates.
biker jk said:Ten Dam said there was a headwind, as did the commentators (Phil and Paul).
karlboss said:Whilst quoting my estimate you wrote this.
If you don't mean in response to my estimate, why quote me?
Alex Simmons/RST said:I was referring you to where I said "Assuming that's the case,...", meaning we can't really and coupled with power from speed estimation based on a windy climb is folly, or comes with largish error bars.
The fact that we have a power file (assuming it's correct as well) from a rider that was ~20-minutes slower and finished with a group of 10 riders may help to get us to narrow the error bars a bit but I think there are still too many unknown variables to be pinning a number that precise.
karlboss said:Do you know what the error bars are in this type of estimation?
Alex Simmons/RST said:2.5m/s is not a particularly strong wind. On the Beaufort scale that's rated only as a light breeze, only 2 out of 12 on the wind scale.
Le breton said:To feel a 2.5 m/s wind at bike level, the wind 10 meters higher must be blowing at about 5 m/s.
Vehicles on the side of the road, plus spectators lined up all the way up the climb tend to shield the cyclists considerably, further reducing the apparent wind felt on the bike.
What I don't have a good feel for is the advantage drawn from the intermittent presence of (sometimes many) motorbikes a short distance ahead of the leaders, plus cars/ motorcycles overtaking the racers. They must superimpose a constant uphill draft, but I don't know how strong it's likely to be depending on circumstances.
karlboss said:Original data is irizar's SRM, so no adjustment needed using this method at least for Irizar. Are you saying linearly interpolating from this data I should knock off .5 as there was a tailwind? That seems odd. That would imply it affected Froome but not Irizar
karlboss said:Ventoux:
Irizar from SRM 324W at 76kg 15.67kph
Froome 22.86kph
Assuming power to weight is directly proportional (324/76)/(15.67/22.86)=5.95Wkg
Take from it what you will, I'm not claiming any sort of accuracy with this method, I already know of a number of them.
Ferrari said:Now, assuming the aerodynamic efficiency to be equal for all riders (something that IS NOT...), considering the square speeds, the difference in power would be represented as follows:
Froome: 54.0 Km / h - 2916 (v2)
Porte: 52.3 - 2738, -6.5%
Mollema: 51.3 - 2635]
http://www.53x12.com/do/show?page=indepth.view&id=138
Alex Simmons/RST said:Greg Henderson tweeted he had a strong tailwind for the climb.
karlboss said:
Alex Simmons/RST said:
acoggan said:Note the date of that blog entry.
Bumeington said:Where did you get the speed numbers from? I make it Irizar finishes at +19:20, so with Froome at 59:00 for the entire ascent, and I'd go with a power of 1.25 in the proportionality to get 6.08W/kg for Froome. With a direct proportionality it would only be 5.66W/kg.
Also, (324/76)/(15.67/22.86) = 6.22 W/kg
Eshnar said:Power to weight is not directly proportional, not even power to speed is...
Alex Simmons/RST said:I'm not sure we can really say to be honest, since there are unknowns with the errors as well.
The same site seemed to confuse the impact of an error in CdA (which would have a relatively small, albeit not insignificant, impact on estimation of power from VAM) with an error in the wind velocity assumption (which would be a very significant source of error in estimated power from VAM).
Like I've shown before with ADH climbing times, you can have a spread of 1W/kg in an estimation of power from VAM with only a marginal wind variance of +/- 2.5m/s.
2.5m/s is not a particularly strong wind. On the Beaufort scale that's rated only as a light breeze, only 2 out of 12 on the wind scale.
Wind matters a lot when determining power from speed, or speed from power, no matter the gradient.
An error in wind assumption can lead to a large error in either speed or power derived from the other.
Put it this way, if you can see flags fluttering on a mountain, forget about doing VAM to W/kg calculations.
I highly doubt that (though I don't have data so I can't say I'm sure).karlboss said:Correct, but uphill they should be close.
Tyler'sTwin said:
131313 said:I can't see the link, but I'm glad to see at least one person is asking the right question.
All of this "wind speed", "power calculation" stuff is complete nonsense. Unless there's a rider in that front group with known weight and a well-calibrated power meter (two very big "ifs"), determining w/kg is going to be fraught with enough error that it's completely useless to make any determinations regarding doping. This is particularly true on a climb like Ventoux that has high, variable winds and is exposed. Plus, strategy and race situation always play a part.
The real question is "how much more power did Froome have to put out compared to the other guys". If Ferrari's calculations are correct, then the answer is "a lot". Enough of a difference to be plenty suspicious, particularly given Froome's pedigree. >10% over the next non-Sky rider isn't exactly "marginal", it's the advantage you'd get with a very well-orchestrated doping program.
Eshnar said:I highly doubt that (though I don't have data so I can't say I'm sure).
Power is directly proportional to weight only in vacuum, but air drag accounts for a consistent part of a real power output, and it is not related to weight at all.
For istance, if I take for true froome's average speed of 22.86 kph (--> 6.35 m/s) above posted, the power output due to weight-lifting only is simply (roughly, assuming the average gradient as 7%) Pw=0.07*69*9.8*6.35=300 W
which is quite low, hence all the remaining power Froome produced (how much? 100 - 150 W ) is due to drag resistance (for the most part) and therefore not proportional to weight.
131313 said:The real question is "how much more power did Froome have to put out compared to the other guys". If Ferrari's calculations are correct, then the answer is "a lot". Enough of a difference to be plenty suspicious, particularly given Froome's pedigree. >10% over the next non-Sky rider isn't exactly "marginal", it's the advantage you'd get with a very well-orchestrated doping program.
It was referring to the ITT, not the Ventoux stage.Alex Simmons/RST said:>10% more power than next non-Sky rider?
Quintana finished 29 seconds down on a climb that took nearly an hour. That's less than 1% difference in speed. That is most definitely not going to result in a more than 10% difference in power.
I can't see that linked website, so can't really comment or not if that's what they actually claim, but if it is, it's nonsense.