MyWindsock?

Rob Lloyd

Rob Lloyd

Well-Known Member
Does anyone use the MyWindsock app for Strava? It seems it's primary purpose is to tell you the impact the weather had on your ride.

But, it also can tell you the CDa of you bike if you use a powermeter (and pay $10/yr for premium services - which of course I did).

I used it to calculate my mid-racers CdA at all of the 'virtual' TT's I did with Larry O since 2019 (since I installed the Powertap Pedals). My CdA varied from 0.170 to 0.192 over the last 5 weeks in 2019, and the first 6 weeks TT's into 2020. Then, suddenly from wk7, my CdA jumped ~0.03; now ranging from 0.202 to 0.237.

According to the calculator on Recumbents.com, that 'costs' almost 1mph at 230w.

What happened?

Hmm. I originally built this bike with a 'nice' (looking) aero carbon fork, but it was from China. After the 2020 Wk6 TT, I found the steer tube had been pulling out of the fork crown. It was junk. So, I swapped in a steel fork I had. Not as aero, but pretty close (I thought). I guess not.

I ordered a new carbon fork. Still from China. I hope it's better quality.

Anyone know of a good source for TT-style forks with disk brake mounts?
 
Don1

Don1

Guru
Just knowing what your cda and segment estimates is worth $10 bucks a year... my road bike cda is .340 but my recumbent cda us like .117. if you run heart rate n power every time you ride it's silly not to go premium on Strava. It unlocks fitness,fatigue levels and progress, just heaps.
 
V

vosadrian

Guru
So is the CdA of myWindsock giving comparable results to other commonly used methods (I used bikemetrix recently)? Would be worth a bit to me to have it just appear rather than have to load to a seperate app. Also, can you apply it to previous rides you have done before you get it?
 
Rob Lloyd

Rob Lloyd

Well-Known Member
Yes, you can apply it to old rides. Just load them up in MyWindosck and select the 'Send Activity Report' from the menu; it will then add the data to your Strava activity description.

Of course, you can view the data in much more detail on the MyWindsock dashboard. It will show you the calculated CdA at each point in your ride. I'm not sure how they combine that data into a single value, but it seems very reasonable to me for my bikes. It's also reasonably consistent.

My mid-racer comes back at roughly 0.20. When I raced a TT earlier this April, I wore a heavy sweatshirt (definitely not skin tight) and my CdA for that ride dropped 0.02 (to 0.22 or so). So, you can definitely 'see' the effect of even small changes to your aero profile.

I really want to take my laptop with me to the Willow TT loop and do some testing.
 
V

vosadrian

Guru
I just joined up. Seems pretty good. Getting similar CdA to what I was getting using bikemetrix but with a fraction of the effort to get it. I do seem to be getting pretty low CdA numbers (around 0.18). But I am not sure if my power meter might read low. I have a single sided Gramin Vector PM. I have a dual sided on my DF so I might swap that on. On my DF I was always very close to 50% L:R, but perhaps I am not on a bent?

Interesting that where I live went into COVID restrictions about 6 weeks ago. This changed the riding loops I have been riding since I am not allowed to ride in some areas. This also happened the same time I fitted the Brain Box to my V20. I only have a few rides with my good aero wheels (and no Brain Box) on the old loop to look at... but I was getting CdA around 0.15. So I can't really tell if the Brain Box is worse CdA than without or the roads were just faster before (more open, less hills, smoother road surface). I will have to do some testing at some point!
 
ccf

ccf

Guru
Surprisingly, it shows wind and CdA for Zwift rides. My CdA for the ride I did on the Tick Tock route of Watopia on Saturday ranged from 0.22 to 0.27. It shows wind speeds from 20.8 to 23.5 mph. I wonder where the wind "data" came from?
 
V

vosadrian

Guru
I wouls say it uses zero wind if it can't get a weather source... although doesn't Watopia have real GPS coordinates? So maybe it has data for the weather at that GPS position?
 
ccf

ccf

Guru
That must be it. From Zwiftinsider: “Watopia is located on the much smaller Vanikoro Island (also part of the Temotu Province), approximately 90 miles southeast of Lata.”

So I guess Mywindsock is using weather data from Vanikoro.
 
V

vosadrian

Guru
I think this is gooder thread as any to ask this... I find with MyWindSock that getting fairly repeatable and consistent CdA data is very easy. You don't even have to do anything... it is just there. I know that this was available using other platform with more effort for some time (years), and I am sure some riders go to the trouble to document there CdA development over time using those platforms. What does surprise me is that when I do a search for CdA analysis of various changes to a recumbent bike (like adding a tail box, going to a covered rear wheel etc.), I can't find anything. I am surprised more people have not used these tools and discussed the results on forums etc. I was just interested in seeing what other people had found so I could decide if the effort was worthwhile to attempt these improvements, but seems I will have to experiment myself.

On another note, I was curious to analyse some of my older rides with MyWindSock. I started using a power meter back in 2015 and I was fairly active in road bike racing at that time. I have always found my power meter data has read lower than others. I have always used Garmin Vector power meters. I have some solo road bike rides with CdA under 0.2 which is surprising and I can only put down to a low reading PM. But I was curious what the effective CdA was when I was in a race riding in a fast moving bunch. For me I have some races where the calculated CdA was around 0.14 which is better than my best on my V20 (around 0.15-0.16). Many people say a recumbent is quicker than a peleton... but in a large peleton where 90% of the riders are cruising with an effective CdA lower than a fast recumbent, it is going to be tough to beat them! If you have not ridden a DF in a large motivated bunch, you can't appreciate how quick you can go at fairly low effort!
 
Rob Lloyd

Rob Lloyd

Well-Known Member
Yeah, I found my CdA is pretty consistent, within a range. For some reason, the range on my mid-racer is more than on my LWB. Maybe because it's more aero (~0.2 vs 0.32 for the LWB bike). The mid-racer has been as low as 0.17, and as high has 0.23. The 'high' I can somewhat justify as clothing and experimenting with camera mounts. But, I can't justify the 'lo' reading of 0.17. There was nothing different on that ride than a similar one at 0.19 or 0.20.

I really want to get out to a test loop and try some different things. With enough runs, should be able to even do some statistical analysis and see if there really is a difference between different setups.
 
V

vosadrian

Guru
Mine are always on the low side. I put it down to my PM reading on the low side. If a PM reads 10% lower, the CdA will be 10% lower. My highest CdA reading on the V20 is 0.189 when I had the Brain box that was too high on the back and 50mm wheels. Lowest recently is 0.149 with the deep wheels and no brain box on the loop with smoothest roads... but typically more recently with that setup I hover around 0.16. I am planning to add a custom tail box (but not large like the real aero ones) and see how that effect things. Then I want to enclose the rear wheel and see what effect that has.

I suspect my true CdA readings are probably around 10% higher, as I feel my PM reads around 10% lower than others.
 
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