CDA estimators reliable?

So I know golden cheetah, best bike split and my wind sock give cdA estimates was wondering if anyone knows how they compare to each other and to more accurate wind tunnel or velodrome testing. My wind sock gives me a 0.22 for 40k leg of Olympic tri which I did in 57 min on 239np so I think I was reasonably aero but not sure if I would get vastly different numbers with others above. I’m planning on using my wind sock to dial my aero position and gear but would feel better if it’s actually reliable.

If you are really serious about the results you should use all three. If they all agree about the relative CdA difference between a few different setups that you tested at the same place on the same day with the same power meter…well then you might just have a valid result! :smiley:

@Niscshne I’m not the best person to give advice about aero testing, but here are a few things I’ve learned.

Bring your scales. Weigh yourself between runs just to make sure that is controlled. Zero your power meter between runs. I have a 0.5% air pressure gauge that I used to normalize air pressure between runs.

The most likely thing to screw me us is Crr. You know…take off the disc wheel that’s set up to run tubeless with mfg recc’ed amount of sealant…put on the tri-spoke with latex tubes…walk away thinking the tri-spoke is the MOST AERODYNAMIC WHEEL EVER when actually it just has much better rolling resistance.

Even though myWindSock and BBS integrate weather data you are better off going out early in the morning on days when wind is less than 5mph.

Try to pick a location that naturally keeps winds constant. If you can find a loop on some dikes around a river that can be a good choice. Or a loop around some sort of small plateau. (probably an indoor velodrome is a better choice but I’ve never tried it. There might be some considerations there I’m unaware of)

Try to pick a gps setting that gives you the best location data. Error in GPS can wreck your results. Also, try to eliminate any deviation that you personally have on the route. Try to always do the same distance to w/in inches.

Ive used the chung method on golden cheetah. Im doing it on a 1.3km circuit, so that makes things a bit easier. Doesnt really matter if its accurate, so long as its precise. If you can repeat results on multiple runs with the same equipment/position then thats better than being accurate, as you can compare your change.

Generally if making a change to equipment or position its recommended to do A/B/A/B runs for the two setups so changes in conditions have less impact. This is pretty hard if its a big change, so make your own judgements.

I had all sorts of problems at first, but after getting a speed sensor on the bike it all worked much better. The GPS data was cutting corners and under-reporting distance, also reporting distance inconsistently.

Calibrate PM before each test run, keep consistent tyres/pressures and off you go


I’ve been manually matching a my windsock CdA to my power/time but I am calling it my effective CdA as I guess it would be calculated on a constant power and not easing for downhills/ bends/ traffic, it won’t handle driver train losses and I suspect that there’s tons of other variances that means it can’t be a definitive CdA.

Timely podcast topic from Scientific Triathlon (That Triathlon Show) Podcast