08 July 2015

The Gorilla Gets #2 in TERRIBLE Weather!

Modeling the Tour de France is for me as much fun as watching it.  Using the laws of physics, real-world models for cyclists and their equipment, and models for complicated terrain, I feel like a giddy kid (a MUST feeling for a scientist!) when we hit stages within a few percent.  There are, however, stages for which I know our predictions won't be great.  Northern France and its weather have hit us pretty hard in past few years, leading to prediction errors around 7% - 8%.  That happened again today, and I knew it from the moment the race started.  Below are some screen captures I put together into a single image (click on the image for a larger view).
The above images came after an early crash.  You'll see flags in the first image revealing treacherous crosswinds that reached 35 kph (22 mph).  The bottom image shows Teams Sky and BMC getting pelted with rain.  Weather made racing so bad that there were no chase cyclists; teams simply stayed bunched together.  Crosswinds and rain were responsible for splitting the peloton in two, and for the big crash, shown below, that happened with about 25 km (16 mi) left in the stage (click on the image for a larger view).
Knowing that we were going to be too fast, I was hoping for a great sprint into Amiens, but riders had to contend with a 25-kph (15.5-mph) headwind, as shown below (click on the image for a larger view).
I grabbed that screen capture with about 10.4 km (6.46 mi) left.  Look at that French flag!

The last kilometer did provide a fantastic sprint.  Because the bad weather meant no one could break away until very close to the finish, all the best sprinters were vying for the win.  André Greipel prevailed and got his second stage win of this year's Tour de France (click on the image for a larger view).
Below is a comparison between the actual winning time and our prediction.
  • Stage 5:  4h 39' 00" (actual), 4h 19' 08" (prediction), 19' 52" fast (-7.12% error)
I can live with a 7% error, given today's weather, and the error is in the right direction.  It's not an excuse to note that we can't predict the weather.  Greipel's average speed is given below.
  • Stage 5:  11.32 m/s (40.75 kph or 25.32 mph)
For all the bad weather, today's stage did get viewers to think a bit about the past.  Riding through areas where fierce and bloody fighting took place during World War I, including the Battle of the Somme, cyclists passed several memorials and cemeteries.  Seeing so many graves of so many heroes was truly sobering.  That riders from countries at war with each a century ago are shoulder to shoulder in a bicycle race is wonderful.  It's too bad there are places in the world today where groups are killing and oppressing people.  Let's hope events like the Tour de France continue to soften hearts against hatred of people different from ourselves.

Stage 6 begins in the commune of Abbeville and takes riders 191.5 km (119.0 mi) southwest along France's northern coast to Le Havre.  Our prediction for the flat stage is given below.
  • Stage 6:  4h 24' 45" (prediction)
If weather off the English Channel does to tomorrow's stage what it did today, we'll once again be too fast.  I'm hoping for great weather and fast racing!

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