How should you measure your CdA?

Triple Danish time trial Champion, Martin Toft Madsen talks about test protocols that yield more speed

Martin Toft Madsen is a triple Danish time trial Champion and holds the Danish hour record. Aside from his exceptional athleticism, he is known for an obsession with data, training and details - a focus that has earned an enviable palmarès which he continues to build, targeting National TT and possible Olympic titles in 2020.

Why does he train with Notio? What protocols does he use to measure CdA? We spoke with the engineer and athlete recently to find out. 

How often do you use Notio in your training? 

During the season, I’m using the Notio three or four times a month. That’s on the high end for a casual user. But at my level, it’s harder to find gains.  

What’s your testing protocol on training days? 

Notio will show you some easy opportunities to ride faster with consistent use. The first thing to do is decide what you want to test. Is it helmets? Is it bars? Is it skin suits?

From there, you need to be organized and get the necessary tools needed for your test laps. Items that are harder and more difficult to test - adjustments that take 15 minutes to tweak, for example - I tend to test over and over so that the data is sound, and I get an accurate picture of my CdA in a single session, even if that means doing 8-10 laps with that set up.   

If it’s a helmet test, for example, one versus the other, I’ll plan generally for six laps to compare - three with the first configuration, three laps with the second configuration. When that's done, I go back to the baseline set up and do a few more laps to make sure I’m testing to the last watt and to also determine conclusively that the measurements are sound.

From there I take the mean data from the test laps and account for standard deviation to see how all the data lines up and what set up had which CdA values.

Where do you train with the device? 

I use an old closed airfield without any cars for testing. I don’t have to worry about breaking and I’m totally undisturbed. I’ll do 2.7km laps and repeat as many times as possible depending on what I’m testing to make sure I get good data. I’ll generally do at least 6 laps with a specific configuration; more if it’s a position change that’s more time consuming so I don’t have to repeat that test on multiple days.  

How do you know your data is accurate?  

The key word with accuracy is repeats. You want to measure a configuration as many times as your schedule allows. When I start measuring, I’ll sometimes do twenty laps, 6-7 laps at a time with a specific configuration. Then I’ll go and look at the average and standard deviation to see where there might be room for improvement.

Generally I would say it takes a couple days of use before you really understand the Notio, accuracy and what you’re doing. Repeated use establishes trust in the device and your protocol which then lets you trust the data.  

How do you recommend starting out with the Notio? 

When you first use the device, take time to get to know it. You need to make testing systematic, so that when or if something goes wrong, you can spot the error. There’s no substitute for a good and standard protocol.  

What I sometimes do is test one thing 20 times, just to get some data. Then you can go from there, looking at if gains of 5 watts or more are enough or you want to dig more. It’s very much an iterative process. If all 20 laps are close within a couple watts, you can probably get away with a single measurement in subsequent tests. If there’s a greater deviation, you can start by establishing your own protocol to see what future changes might help.