Thursday, September 8, 2011

Vuelta 2011: Cobo on the Angliru

Arguably the most epic stage of this year's Vuelta was Sunday's race to the mighty Alta d'Angliru, arguably the toughest steep climbs in professional bike racing.

Here's a profile of the climb, from Climb by Bike:

In the stage, Geox's Juan José Cobo climbed away from the group of favorites, including Team Sky's 1-2 in overall GC, Bradley Wiggins and Chris Froome. Some argued that it was a sign Cobo was dipping into the special sauce, a result too good to be true.

While I realize VAM is subject to many sources of variability and is hardly a valid test of doping, I can't resist running the numbers here. Fortunately I managed to take time splits for each of the final 10 km for Cabo or the group containing Cabo, although I had to guess a bit at 6 km to go, where Cabo was trailing Anton. I guessed that Cabo was around 5 seconds behind here, although I didn't see this explicitly on the Eurosport coverage which I was watching on the web. These times are on the crude side and each of them probably has error bars of up to 3 seconds either way, not even counting the possibility of variable delay in the video on the web channel.

Then to calculate VAMs I needed altitude data. Unfortunately the altitude data provided by or Altimetrias are provided only each km measured from a start to the climb, and since I was recording at points which were even kilometers from the race finish, I needed to interpolate. My first approach was then to tap into some data from Garmin Connect. However, the Angliru is a twisting climb, with plenty of temptation and opportunity to take wide lines through corners and even traverse (as Bradley Wiggins was seen to do). These moves result in a lengthening of the rider trajectory which causes a reduction in the apparent grade. The Vuelta distance markers are likely set under the assumption of the path a car would take. So I was back to ClimbByBike. Fortunately the Climb by bike profile seems to match up well with the Garmin data until the steep bit where, predictably, the rider chose a path to mitigate the brutal grade:


The 17.5% grade shown in the plot is only for the steepest kilometer. The climb pops over 20% on numerous occasions but only briefly. Digression: interesting comparing this to Mix Canyon Road, often considered the toughest climb within driving distance of San Francisco:

Mix Canyon

Needless to say Angliru is tougher... Anyway, back to the topic.

The Vuelta web site claimed the KOM marking the top of the climb was 600 meters from the finish. This makes sense from the timing, corresponding to Cabo riding 44 kph along this portion. It was a twisting gradual descent so 44 kph seems no more than 10% low. So I used this to align the ClimbByBike data with the course. I assumed the KOM was at what ClimbByBike considers the end of the climb. This was 550 meters after the previous km point there, so since this was 400 meters past the 1 km to go banner, I assumed an offset in even km points of 150 meters between the two data sets.


In 2008 Alberto Contador won the stage on this hill. Cozy Beehive assembled the videos of that stage, which show Contador climbed from 4 km to the finish in, to to second, the same 15:25 I calculated for Cobo this year.

Despite his amazing climbing this year, Cobo still used a 34×32 low gear, the smallest of the top riders on the climb. It's another nail in the coffin of the "tough it out" old school thinking on gearing for optimal speed on climbs.


Kevin said...

So what is your conclusion please? If he rode as fast as "Old Contador", well then that makes me wonder about cleanliness ... how about you please? Thanks.

djconnel said...

Well, of course I wonder, but I can't draw any conclusions from just this race: it's a moderate length climb with a minimum of rolling and wind resistance. Still, on day 3 of a brutal 3-day set of stages, as I said it does cause one to pause.