Great power, great responsibility. Less power, greater speeds

22 Jul 2015 Posted by
“With great power comes great responsibility”, the Spiderman quote invoked when Sky revealed Chris Froome’s power data from his victory in the Pyrenees last week.  Only problem – according to the data, with LESS power, came greater speeds, and something didn’t quite add up.  Or many things.

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5.78W/kg to ride away from the best, even while they ride above 5.8

Physics reared its ugly head in the Alps today, when Sky revealed that Chris Froome’s dominant ride in the Pyrenees last week was the result of an effort of 5.78 W/kg.

One small problem – other cyclists had already released their power output from that climb (to add to a growing body of this data).  And theirs is higher than Froome’s level at the dominant front end of the race, yet they rode that climb slower.  By a lot.  According to their power files, Robert Gesink produced 5.8W/kg on the very same climb (using a mass of 71kg, since three separate sources list him at 70, 71 and 72kg).  He lost 1:33 on the climb.

Then Laurens ten Dam, who publishes his power output regularly, lost 4:25, while riding at 5.5 W/kg.

So now we have the kind of problem that made me think back to my undergraduate physics courses, where eccentric lecturers would confuse us with bizarre quantum physics concepts.  In this case, you have Rider A, Froome, producing less power, but traveling faster up a mountain than Rider B.  Then there’s Rider C, Laurens ten Dam, producing 5% less power and riding 10% slower.

So, we are to believe that 5.78 W/kg goes 1:30 faster than >5.8 W/kg, and 4:25 faster than 5.5 W/kg.  One comparative value, you could debate and dismiss the accuracy of that comparison.  But here are two comparisons, plus the fact that we know from riders like Thibaut Pinot, who has published his data, that 6 W/kg for 40 min is the level at the front of the Tour, and this value of 5.78W/kg does not make sense in the known physical universe.

Consider the implication of that 5.78 W/kg value being accurate – the best climbers in the world – Contador, Nibali, van Garderen, Gesink and Quintana – were dropped, some easily, by a performance which historical data, actual data, estimates and released power from a podium finisher has shown is typically possible for around 10 – 20 riders per stage.  No way, no how.  The reality is that 5.8 W/kg gets you into the front group, it doesn’t blow the front group away.

It is thus absolutely inconceivable that a ride of that level, where Froome was supreme on the day, was only at 5.78 W/kg.

I suspect (against my inner skeptic) that part of the reason for this may be benign and innocent.  Kerrison took Froome’s measured power output of 414W, and reduced it by 6% to account for a measurement error due to asymmetric chain rings.  That brings the power down to 389W, which is then divided by Froome’s mass of 67.5 kg to give the 5.78 W/kg number.

The manufacturer claims the error is not 6%, but more likely 4%-5%, so that may account for part of it.  Then there’s Froome’s mass.  On SA TV last year, he said he raced the Tour at 64kg.  A month ago, at the time of the Dauphine, he was at 66kg (while on this subject – we’re debating power files, with all their issues and errors and room for interpretation, but we have this clandestine approach and tap-dancing and evasion around a simple thing like mass?  There is little hope for transparency).  

Anyway, had the measured power output of 414 W been reduced by 4% as per manufacturer, and then divided by 66 kg (surely you won’t race the Tour carrying 2kg more than the tune-up race?), the resultant relative power output would be 6.02 W/kg.

That’s the kind of power output that could create a 1:33 or 2:04 gap to men riding at 5.8 – 5.9W/kg.  We know this because power files from the front of the race on both days in the Pyrenees show that the top selection is riding at around 5.9 W/kg for the duration of these climbs.  The fact that the estimated power output is very close to this supports it, but if you want to dismiss the estimates, it really doesn’t matter too much, because the value is known.

I also cannot understand why Sky would not support their own data with numbers from Porte and Thomas on that same climb. Remember that Porte finished that day 0:59 behind, with Thomas 2:01 down.  Perfect, convenient time gaps, and they could have helped to shore up the data, because if Froome is at 5.78 W/kg, then those team mates should be sequentially, predictably lower (W/kg) and slower (km/h), if all were above board.

If then, the Sky position is that the estimates (and Gesink, Yates, ten Dam, and dozens of other files seen from the front of a Tour summit finish) are wrong, and that 5.78 W/kg is indeed sufficient to ride away from the best Tour field of recent years (form notwithstanding), that position would only be helped had Porte’s and Thomas’ numbers been added.  This is why comparative analysis is important.  So easy.  Yet seemingly so difficult.

What is more, neither 5.8W/kg or 6.1W/kg is ‘mutant’ or ‘extra-terrestrial’ (pick an adjective), as I explained in this article, unless of course you have a cyclist with a VO2 max of only 76 ml/kg/min, then you’d need some pretty remarkable compensatory physiology elsewhere to make it feasible.

Who knows? Ultimately, for what feels like the millionth time, the performance data cannot and will not provide PROOF of doping, or no doping.  If you’re looking at performance to reveal doping, keep looking.  You’re short dozens of pieces of this puzzle, and conceptually, all the limitations can (and are) be acknowledged.  If you are preoccupied with a single value, save the debate and dissent, there is none.

And since Sky gave a little, I hope other teams follow suit.

But the secrecy around these issues, and the confusion and obfuscation, hardly helps.  I hope the Alps provide some fireworks, and I hope more riders from the front of the race release their power output files, because the sooner 5.78W/kg is consigned to the internet junkyard, the better.

Ross

Note: An earlier version of this article included power output from Adam Yates as a comparison to the Sky value. That has been removed since the file could not be verified as being in public

This post is part of the following threads: Tour de France Analysis, Tour de France timeline – ongoing stories on this site. View the thread timelines for more context on this post.