Aero Tech #2 — How Fast is your Track?
The track cyclist’s biggest enemy isn’t always other riders while out on the boards. Aside from a necessary mental strength to power through, the greatest battle to overcome is air resistance. At a speed of 50 km/h (31mph), about 90% of the riders power output is used to overcome the force of air upon the rider.
Over a series of blog posts, I will break down track cycling aerodynamics and respond to my research with a series of innovative concepts and product designs.
In this post, I will discuss air pressure and the resistance it can cause on a track cyclist. I will explain the impact of temperature and altitude in relation to air pressure and provide you with a tool to assess the conditions of your local velodrome yourself.
People have often confused an indoor velodrome to be a purpose-built closed in cycling track without any air to slow you down. Well in fact this is wrong. It goes against the laws of physics and would be incapable of supporting human life. A place without air - known as a vacuum is like outer space, an expanse of not much. An indoor velodrome on the contrary is built in a way to consistently maximise the efficiency of the cyclist, but indeed, there are still forces trying to slow you down.
Indoor velodromes are built eliminate natures variables such as wind, rain humidity and temperature. Air-conditioning can maintain a stable temperature all year around, but closing in a velodrome from the outdoors doesn’t always affect the variable of air pressure.
There are 2 main elemental variables that can change how fast a velodrome is on any given day:
Air pressure is the weight of air pressing down on the earth, or how I like to describe it, is the density of air molecules in a given volume of space. The lower the air pressure, the fewer molecules banging into (and resisting) whatever is moving through it.
Air pressure can change based on temperature, humidity weather conditions, and altitude. A velodrome at sea level will be slower than a velodrome at a higher altitude. The Mexico City velodrome at 2230m above sea level can give an advantage of about 2.5kmph just from having a lower air pressure.
Even if indoors with a controlled temperature, A velodrome at sea level may be quicker on a stormy day than a nice and sunny day as the air pressure is lower.
Temperature is much easier to control than air pressure. We control air temperature every day using heaters, or refrigerators to regulate and control heat in a space.
Air temperature is proportional to the kinetic energy generated between vibrating air particles. When air pressure drops so does the temperature. There is more resistance in the air with lower temperatures.
Thermal vibration of molecules. The vibration increases with temperature. Image Source: https://en.wikipedia.org/wiki/Temperature.
When we combine a low air pressure (caused by a high altitude or an environmental weather change) combined with a high temperature, we can reduce the friction air plays on the cyclist. Indoor velodromes around the world are generally kept at around 25 degrees. This temperature is considered optimum as higher temperatures can impact the riders ability to intake oxygen or overheat - limiting performance.
Measure Your Velodromes Air Pressure at Home
A great app we use at Velobike is called AutoDens. The app is available on Apple mobile devices for free on the app store.
AutoDens calculates air density live from over 40,000 airports all around the world. Any given day (or time of day) may have a different air density value based on the temperature and dewpoint variables. The higher this ‘Density Altitude’ value, the thinner the air is and the faster you will go.
Screenshot from the AutoDens App.
To view a current air density, Simply select an airport nearest to your velodrome to get an assessment of the local conditions. You can manually adjust the numbers if you have more accurate temperature data from the velodrome such as an indoor velodrome temperature. Have a play around, notice the ‘Density Altitude’ value and the ‘Air Density’ volume will change with a change in the variables.