Monday, May 24, 2010

running the numbers from the Zoncolan (2010 Giro d'Italia stage 15)

Yesterday's Giro stage finished on the epic Zoncolan climb, a truly brutal slope which I've vowed to climb myself some day. If numbers alone can induce pain, these numbers surely qualify:

Zoncolan profileZoncolan profile: ouch!!!

I watched the last 50 km on (linked via CyclingFans): absolutely riveting stuff. Sure, L'Alpe d'Huez has its character and history, but the mighty Zoncolan is in a separate category of "beyond". With the pathological gearing used by riders on the stage (for example, 34-52 front with 11-29 back), riders were at least able to maintain a decent cadence, but that couldn't hide the brutality of the slopes. This hill is truly every rider for himself.

Given this, it's interesting to see what the numbers say about what transpired on the mountain. I took a few time checks from the main group (ignoring the break) starting at the 10 km to go point. The climb "officially" begins 100 meters sooner. But it didn't appear to me there was much of a grade, if any, in these first 100 meters. I estimate the pack could cover that in around 8 seconds, time which should be considered for comparing times reported for the climb.

From this pack, it was initially a war of attrition as one rider after another fell off the pace. Finally, it was just Ivan Basso, Cadel Evans, and Scarponi. Scarponi was the first to fall back, while Evans bravely struggled on, fighting to avoid showing Basso any weakness. But finally Evans, too, was gapped off, leaving Basso to solo in for his greatest victory since his two year suspension from the Puerto blood bank affair. Evans regrouped a bit, regained Basso's pace temporarily, but then lost more ground approaching the finish. Scarponi almost recaught Evans, but not quite, finishing third.

Here's my data from Evans and Basso:

kmsecsgapmetersgradekphnet kphVAMnet VAMW/kg

kmsecsgapmetersgradekphnet kphVAMnet VAMW/kg

The key numbers are probably "VAM", the rate of altitude gained between time checks ("net VAM" is the rate from the 10 km point), and "W/kg", which is my estimate of the power delivered by each rider to his pedals. To estimate this, I assume extraneous mass (bike, clothes, etc) was body mass / 8. I then assume CdA = 0.3 m² / 50 kg body mass. Further, CRR = 0.5%, mass density = 1.1 kg/m³, and drivetrain efficiency = 97% . I assume uniform grade between "time checks" (this affects only wind resistance, which is small and uncertain anyway). Daniel Coyle says in Lance Armstrong's War that a rider needs to be able to sustain 6.7 W/kg to win the Tour. During the EPO era, this has certainly been typically the case: power estimates during sustained climbs tend to be close to this. For example, Alex Simmons estimated Contador delivered 7.03 W/kg climbing Verbier during last year's Tour de France.

So first it's clear neither of these guys were climbing to that standard, which is a nice rebuttal to those who claim Basso must be back on "the program". Indeed, Gilberto Simoni, who's clearly not on the program this year, was able to climb the same hill with a VAM of 1850 m/hr in 2007, for which I'd calculated a power-to-mass ratio of 6.28 W/kg. Even that power is below the Contador/Armstrong standard of "excellence".

But these numbers also are telling tactically. It appears Evans made a mistake trying to follow Basso's unsustainable pace from 5 km to 3 km remaining. Evans would have been better off riding his own pace, then managing or even perhaps closing the gap which Basso was able to open. You can see Basso faded toward the finish; Evans, however, faded even more. Evans should have practiced the patience which won him Fleche-Wallone, where he let Contador have a gap on the final climb of Mur de Huy, only to close that gap then pass Contador for the victory. Perhaps Evans overestimated his strength.


Justin said...

Dan -- Did you see the article on cycling news where Sassi says Basso did 5.68w/kg, 395 watts for the whole ~ 40 minutes on the Zoncolan? Basso had an SRM on his bike, so presumably this was his measured power.

djconnel said...


I get 6.08 W/kg. That's very curious. I'm not sure what the cause of the discrepancy could be.

Here's Nibali's crank, which appears to in fact be an SRM (in the past racers didn't have 110 mm BCD SRMs, since they so rarely use compact gears).

EDr said...

Perhaps you included the weight of bike+clothes in that figure? Sassi didn't: 69.5 kg sounds about right for Basso.

djconnel said...

Thanks. Yes -- I assumed everything not included in "body mass" was 1/8th the total body mass. So that's 1.7 kg more than 6.8 kg for the bike alone.

maryka said...

If you add the weight of bike and clothes to the rider's weight to calculate w/kg, wouldn't that come up with a LOWER number, not a higher one? So that still doesn't explain how you got 6.08w/kg unless you drastically overestimated his watts.

395w / 69.5kg = 5.68w/kg

395w / 78kg = 5.06w/kg

78kg * 6.08w/kg = 474 w

maryka said...

Btw, it wasn't Alex Simmons but the Science in Sport guys (Jonathan Dugas and Ross Tucker) who did the Contador climbing analyis post.

djconnel said...

It depends on what side you come from. If you start with rider power and then predict speed, the heavier the bike, the lower the speed (obviously; which is why people spend $$$$ for bikes even 1 kg lighter). In the reverse direction, which is the direction of this post, if you start from speed and try and predict power (or power / rider mass), the heavier the bike, the larger the number.

So I'm assuming quite a low number for mass other than the bike and rider. It's thus possible I'm overestimating rider mass. I already assumed some deviation from the claimed rider mass of 69.5 kg due to dehydration. Maybe he was even lighter than that: 1 kg, perhaps. But there's so much uncertainty from rolling resistance and wind resistance, for example, that it's tough to draw precise conclusions.