Aero Testing
I think it’s clear that we’re not the strongest riders compared to our other triathlon abilities. Certainly, the bike portion is where I have most potential to improve my ironman times and bridge a little of the gap separating me from the prize-money range. While some of it certainly comes down to limited time to train, hours in the saddle that get converted into much needed watts on the pedals, repeatedly the data seems to indicate that some other competitors are much better aero than myself and Daniel. Free speed that I’m simply giving away.
While my position has certainly converged slowly over the years (see pictures), there is still work to be done. With the power meter available, one can simply go out in the field and test how fast the bike is rolling for a given power output.
2016 position.
2017 position.
2018 position.
2019 position.
2020 position.
More precisely, one does evaluate the “virtual elevation” assuming zero wind, or correcting for wind with a captor like the aerocomp or similar. On a calm day, we went out to the panzerpiste with Daniel, a flat section to avoid too much variations in speed, low wind and out-and-backs avoid unnecessary extra parameters to fit, and finally no cars avoid drafting effects. I took my new Ron Aeron X wheel, the MET Drone wide body helmet, as well as the Zipp 858 and the Giro Air Attack helmet of Daniel for the first tests. Two rounds with each setup, summarized in the table and plot below.
| Lap | Description | CdA out | CdA back | CdA avg | CdA std | Time | AvgP | NP |
|---|---|---|---|---|---|---|---|---|
| 1 | MET+disc | 0.2427 | 0.2496 | 0.246 | 0.005 | 4:57 | 308 | 310 |
| 2 | MET+disc | 0.2479 | 0.2392 | 0.244 | 0.006 | 5:01 | 298 | 302 |
| 3 | MET+858 | 0.2531 | 0.2531 | 0.253 | 0.000 | 4:59 | 310 | 310 |
| 4 | MET+858 | 0.2548 | 0.2479 | 0.251 | 0.005 | 5:00 | 304 | 305 |
| 5 | Giro+858 | 0.2766 | 0.2627 | 0.270 | 0.010 | 5:02 | 314 | 313 |
| 6 | Giro+858 | 0.2740 | 0.2661 | 0.270 | 0.006 | 5:02 | 314 | 316 |
| 7 | MET+disc | 0.2522 | 0.2427 | 0.247 | 0.007 | 4:57 | 311 | 314 |
| 8 | MET+disc-fast | 0.2488 | 0.2505 | 0.250 | 0.001 | 4:46 | 355 | 362 |
| 9 | MET+disc-hands | 0.2514 | 0.2453 | 0.248 | 0.004 | 4:58 | 309 | 308 |
Laps 1 and 2 were to test what would have been my competition setup this end of the year. Laps 3 and 4 the setup I had planned for Hamburg, before getting the disc rear wheel. Laps 5 and 6 to see whether a small round helmet would be a good option. Finally, lap 7 to verify long term drifts (such as wind picking up), lap 7 faster, with Daniel drafting not too far, and lap 8 with slightly different hand position (together above the bars instead of gripping each extension.
CdA results.
While the helmet difference is clear, and netting me somewhere around 10 W of gains (at the expense of being hotter), the wheels are much trickier to separate. The Aeron X seems to be slightly faster (2-3 W), but it could also be simply due to the different tire setup (Continental Attack + Vittoria latex tube for the 858 vs Schwalbe Pro One tubeless for the disc, both in 25 mm). Nevertheless, I feel like putting the disc wheel for competition is justified, since it’s just as fast without wind, and I expect it to sail when the wind picks up.
Obviously a CdA at 0.24-0.25 is not considered fast, not even close (and some may be the powermeter calibration, but I guess a lot can be done on the position as well). But it's a baseline to start doing some changes not just by eyeballing it, but with some reliable way to figure out whether it's worth it or not.
In Daniel’s case, the difference is even less clear, as he’s likely better hiding his head when not looking forward. This was just a first test; we’ll be sure to make some more in the next spring when the weather gets nicer again in Switzerland.
In the meantime, here’s a video of my current position, let me know if you have inputs!
