In our second part of our aeroCAST series, we will show you how to you use our aeroCAST tool to calculate your CdA. I will use my race of this year’s Challenge Roth as the baseline for the calculation, the historic weather data, my powerdata and my racetime to make a reverse calculation of the average CdA I had during the specified Challenge event. After you’ve registered yourself on our website, you can log into the modul in our aeroDATA page.


aeroCAST basic data

By clicking the aeroCAST button, you are forwarded to the aeroCAST startpage. What you see are the initial values. In the next step, I need to enter the weather date from July 9th, 2017. Personally, I like to use, a US website which gives me a good wind diagram about the entire day for US competitions, which can be very handy for Kona for example. As an alternative, I also like to look at a second page, in my example


weather data

weather data


I used the data from Weather Underground for my calculations. I converted the air pressure into hPa and the wind direction into degrees. Since the wind was moving between SSW and WSW, I chose SW which is 225 degrees. Of course, you can play a little bit around with the angles in the calculation. I decided to use 220 degrees, 14 km/h as wind speed and used 1012 hPa for the air pressure value. In the next step, I need to use the race data I tracked with my Garmin, which is a little more accurate through the auto stop function. My average power was 240 watts and my bike split according to Garmin was 4:43:12. Since you cannot enter the time in aeroCAST, I am writing the time down on a piece of paper for now. The coefficient of rolling resistance (crr) will remain as it is. Now, the total system weight is missing, which means the weight of my bike, my nutrition and myself. In my case this means 73kg for me and 10kg for my bike and nutrition. All these values are now put into aeroCAST via the switches. I leave the value for driveloss at the default value.


aeroCAST basic data

The last thing missing is the wind resistance, the CdA. I start with a value of 0,26 qdm or 26 aeroPOINTS and choose Challenge Roth as race course via the drop down menu. One more click on run and I see the calculation.

aeroCAST diagrams

Next, I scroll down until I reach the diagram for the CdA values. Since my time was 4:43:12, I look at which values is closest to my time. In most cases you have to play a little bit with the CdA value and restart the calculation. In my example I was pretty lucky with my initial value since I only missed it by 1 aeroPOINT. Therefore my CdA was 0,27 qdm or 27 aeroPOINTS.
Now, we will take a look at the question, on how to use aeroCAST to become a faster you. Therefore, I will do a calculation of the race with my newly calculated CdA.

aeroCAST basic data

By pressing run, I receive the new calculation with my first three graphs and start this time with the power diagram.

aeroCAST power diagram

According to the diagram I can see that to be 10 minutes faster, which means getting close to the 4:30 hrs mark, I would have to push 265 watts, taking into account my current wind resistance. The second diagram shows the time in relation to the system weight.

aeroCAST weight diagram

The first sight already lets me know, that 1kg less in weight and some savings on the setup would give me a maximum of two minutes in time savings. My setup however, was pretty much stripped, since I was racing with one bottle of nutrition concentrate and one aerobottle for fluids. But I will come to the subjects bottles at a later stage in another post. Therefore, not too much room for improvement with the weight. Lastly, I will take a look at the CdA diagram.

aeroCAST CdA diagram

This one shows my time in relation to the wind resistance. If I move to the left on the graph, I can easily see, that with my current aerodynamic value and my average power, I could be somewhere between 4:30 and 4:33 hrs, without training more and investing a lot in equipment. I do not want to state, that there will not be any investment, however I want to show you that it does not always have to be the most expensive equipment. Please keep in mind that the human body makes up between 70 and 80 % of the wind resistance, and here you can save most time without even spending money.

In the next posts, we will show you how this works, how you can save money and still become faster.