Norwegian National TT Championships and Aerodynamics

- Guest blog by Reidar Borgersen

The recent Norwegian TT Championships saw a new national record set, along with several more of the fastest times ever recorded at this event. What’s behind this new level of performance?

Tobias Svendsen Foss set a Norwegian record of 56:54.5, at an average speed of 52.7km/h. Søren Wærenskjold was not far behind at 58:13.3, while Andreas Leknessund (who held the previous Norwegian record) took the bronze with 59:20.5.

What I think is almost as impressive is how close the rest of the field was. Daniel Årnes and Asbjørn Slagtern Fjellvåg at 59:24 and 59:30 respectively rounded out the top five, meaning all five held speeds of above 50km/h. A little farther down the list, Eirik Lunder took 10^th with 1.00.50 and Syver Wærsted took 20^th with 1.02.00 - in other words, an average speed of 48.3 km/h.

So what made this year’s results head and shoulders above previous years? Have the riders gotten that much stronger?

We can see many of the athletes who competed in the National Championships in this Strava segment – so we can get a look at the watts they’re posting. Foss and Leknessund have not shared their watts on Strava, while Søren Wærenskjold has claimed 430w to the magazine Landevei . The fourth and fifth placed riders at Nationals, Årnes and Fjellvåg, show 402w and 383w respectively, Fløtten 358w, and Lunder 378w. These are strong, but far from superhuman wattage values.

So if it’s not increased power output, what’s making everyone faster?

CdA

To ride faster, there are three forces we have to fight against: gravity, rolling resistance and air resistance. On a flat course like at the National Championships, the air resistance is by far the biggest competitor. We measure air resistance with CdA. Typical figures for a road cyclist are around 0.30, while an elite racer ends up around 0.18-0.23 (lower numbers are better).

To get accurate CdA values we used to have to go to a wind tunnel, which not many people have access to. Gradually, several other methods have been developed to estimate CdA quite accurately. A CFD analysis calculates CdA using data modeling, and is something our partner sykkeltilpasning.no does through STAC. There are also methods to estimate CdA using a calculation involving power output, mass, speed, air pressure, and altitude profile. All of these measurements are available through on-bike powermeters, speed sensors, a pitot tube and a barometer or GPS. We don’t have rolling resistance, but it is independent of speed, so with a standardized estimate we can calculate CdA quite accurately. All these variables can be easily controlled in a velodrome, but in stable weather you can also calculate this accurately on the road. In recent years, we have seen a number of devices that make it easier to calculate CdA accurately even without perfect weather conditions. At Storeskiva we use Notio for this.

We can also use calculators like Mywindsock or Bestbikesplit to analyze the CdA. Let's take some examples from the Nationals riders and estimate their CdA (you’ll see me there at #19!).

Speed ​​and calculated CdA from Bestbikesplit

So we have three athletes who had about the same watts, weigh approximately the same, but ended up in 6th, 19th and 49th place. That seems a little unfair, isn't it? It becomes very clear that CdA has major consequences for an athlete's speed. 

Let’s take a look at what would it take for me to get ahead of Tobias Foss:

To calculate this, we can load the TT route into Bestbikesplit and plot my numbers. With a CdA of 0.203 I would have to push 439w, i.e., 82w more than I currently do, to beat Foss. There are definitely some cyclists in the world who can hold 439w for 57 minutes, but I’m unfortunately not one of them. Should I try to beat Foss by only reducing CdA, then I have to go down to 0.155. At 184cm and 80kg, that’s also highly unlikely. But if we try something in between, reducing my CdA to 0.185 and increasing my watts to 407w, then we have numbers that could be achievable for a mere mortal.

At the age of 41, I will probably not increase my watts by 50 over the next year, but I will help others get more speed. Together with Petter at sykkeltilpasning.no , we at Storeskiva can help you with training, positioning, measuring CdA through CFD, or test you with Notio out on the road.