Finally, the power to change the weather

Those of you reading this in the UK will, undoubtedly, have had multiple occasions in your life where you’ve wished it was possible for you to change the weather. Well, we have good news for you. For the low price of your annual myWindsock subscription you will now be granted this power. Here’s how…

  1. Open up myWindsock’s Surface platform
  2. Scroll down the panel on the left hand side of the screen
  3. Click on the “Weather Override” drop down menu option
  4. Input values to change the weather

Unfortunately, for legal reasons, we are only able to change the weather within the course simulation on myWindsock, we are not able to adjust the weather outside. That said, it’s still interesting…

You go faster when it’s hot

The human body doesn’t love hot temperatures, especially a British one. That said, there’s an offset – as the air resistance of a bicycle decreases when it warms up so you need to produce less power to go the same speed. Bare with us while we do a little bit of maths.

This expression tells us about the power needed (P_aero) to ride at a given velocity (v). You’ll notice there’s a little symbol that looks like the letter p, that’s a Greek letter called rho and in this equation it represents air density. What this tells us is the power required to ride at a specific speed, v, is directly proportional to the density of the air.

Now, air is made up of tiny little particles, mostly:

  • Nitrogen molecules ((N_2)) — 78%
  • Oxygen molecules ((O_2)) — 21%
  • Argon atoms ((Ar)) — 0.9%
  • Carbon dioxide molecules ((CO_2)) — 0.04%
  • Water vapour molecules ((H_2O)) — variable

When it gets really hot, all of these particles whizz around quite a bit faster which means in every cubic meter of air, there’s actually less particles than when they’re moving slowly. When you’re cycling, you have to push each of these particles out of the way – that pushing is the force we feel from the wind and we call it “air resistance”.

Air density is proportional to atmospheric pressure (P – not power this time) and inversely proportional to temperature. When temperature goes up, air density goes down (if all other things are fixed).

This is why you go faster when it’s hot. In real life, the temperature does impact your ability to produce power. But on myWindsock – we can just pretend that isn’t the case…

How hot does it need to be for me to break the Poggio KOM?

The Poggio di San Remo segment on Strava is held by Tadej Pogacar and Filippo Ganna who some how managed to ride up it at 39kph. Neither of them share their power data on Strava but presumably they did quite a lot of watts.

As we’ve already discussed, air resistance decreases when the temperature goes up. That means, you ride faster for the same watts. Imagine a 76kg rider on a 6.8kg bike doing 500W on this climb in a relatively aerodynamic road bike position, with a cda of 0.23 on a windless day that’s 30 degrees. This is 6.5W/kg for around 6 minutes, so pretty good but not alien level world tour numbers.

This gives us a prediction of 6 minutes and 16 seconds. A pretty good time on this segment. But what happens if we change the weather?

Getting the perfect day

We are now going to calculate the conditions required for our imaginary rider to get the KOM on this climb. We will start with the wind…

The Poggio di San Remo segment is twisty enough that if we turn the wind up too much, the headwind section slows us down more than the tailwind speeds us up…
Wind Speed (m/s)Segment Time (min:sec)
06:16
56:09
106:07
156:12
As it turns out, 10m/s is the optimal wind speed (at 30 degrees with this cda) on this climb. Any faster, and the headwind section slows us down more than the tailwind speeds us up.

We need to find 37 seconds to get that time down to 5:30. We will use our optimised wind direction and wind speed to increase the temperature until we find that extra 37 seconds.

Temp (degrees C)Segment Time (min:sec)
306:07
406:05
1006:00
Well, looks like we aren’t getting that KOM then…

It turns out, a regular human has absolutely no chance competing on the Poggio with Ganna or Pogacar. Ah well, we tried.

Change the weather here.