tt-postion and side wind

[tmd]

Question one.
I switch the powerpod between my roadbike and my TTbike.

I've read that the powerpod takes the first say 10 minutes to autocorrect itself. When the powerpod is on my TTbike, is it off influence that mostly the first 15min of my ride I'm not in TT-postion (riding out of the city) and only then go to TT-position and thus altering my Cda. I don't mind the powerreadings are incorrect in this section but should be correct when in TT-position.
Or does this autocorrect only occur after a bike switch?

Second question:
I live in a very flat and windy country, the Netherlands, and I've noticed on several rides that when riding roads that turn left, right, left, right. The powerreadings during the sections with severe wind from the side seem to be too high.
When riding at say 275W with wind head on, then take a slow turn the power goes to 350W when the wind comes from the side. All the while I try to maintain the same effort. I've regulary seen readings of 400W (3s smooting) and going back to about 275W when riding with head wind again.

TIA

[Velocomp]

1) Your ride position won't influence PP recalibration.

2) Please post a ride file that illustrates your observations.

[tmd]

Thanks for the quick reply.

This ride has some of these irragularities, especialy from the 50min timemark until the 1:20 timemark, it perhaps seems like an out and back ride but it's a loop mostly riden on the dutch dikes.

Guido

[Velocomp]

If the 50 min to 1:20 portion is a true loop, then it would seem that the wind speed would go from headwind to tailwind. However, that is not the case...

Your power does go up in this section, but so does your heart rate; most definitely you were working hard.

Is this file from your TT bike?

[tmd]

No the total ride is a true loop, the 0:50-1:20 section is a section heading west but meandering. So the road follows the river turning left and right but prodominently going in one direction heading west .

I'm defenitly working hard as this is a training ride at which I try to maintain a steady treshhold-pace at certain sections of my ride and this section I was pushing so I paid more attention to the powerreadings to try to maintain a constant force. And almost every time there was hard wind from the side the powerreading where higher then when there was a head-wind even so I was trying to maintain a constant force

I've noticed this on other rides as well, as far as I can recall only with strong side winds.

And this ride is with my roadbike, with the powerpod placed with the standard bracket.

[tmd]

Had another ride where there was a very distinct section with wind from the side where the power was way too high.

It's at the section 1:47-1:49. I make a left turn at 1:45:45 and go from pure head wind to pure side wind, trying to maintain the same afford, but see readings of 300+ while it should be between 200-250 as far as I think.

The road is a straight dike next to the river with no obstacles what so ever, so the wind can do it's job and the wind is blowing from my right side.


Guido

ps I've attached the original file as well as the file I already did a Route analisys on.

PPS By the way previous post was about my roud bike, this ride I did with my timetrail bike so I see the same phenomenonon on the tt-bike as well.

[Velocomp]

It would be helpful if you'd provide GPS information with your ride file, so I could see on a map what is going on...

There very clearly is a wind spike around the 1:45-1:49 mark. The higher head winds is what is causing your higher watts.

The question is: is this increased head wind "real"?

1) I find it very difficult to precisely determine the direction of ground wind when I'm on the bike.

2) "Pure" head wind means there is no component of wind perpendicular to your direction of motion. Are you 100% certain this is the case?

3) If you changed directions from "pure" headwind to "pure" side wind, then I would expect PP to show LESS wind after you make the turn into the sidewind. What you're seeing is quite different...

If you can get a weather map for your area, showing the direction of the wind at the time of your ride, that might be informative.

I honestly don't understand how PP could be showing side winds as stronger in magnitude than head winds.

If you can, try the same route again, but this time riding in the opposite direction. Let's see if we see comparable behavior when there are tail winds...

[tmd]

Thanks for your reply.

I agree with what you say, it's difficult to precisely determine the direction of the wind when on the bike, the feeling you have on the bike isn't always whats rely going on.

I made a little graphic with the relavant information. The weather data I found are from a weatherstation some 10 kilometers to the west so pretty precice. And like you said this pictures the wind not as a pure headwind and side wind alhough I still beleive it was pure side wind. Perhaps the dike I'm riding which is about 5meters high has his influence as well and 10km is far away enough to have a slightly different windsituation.

I'm not trying to bash you're product, on the contrary, I like it a lot.
But I'm tring to determine how to interpretet the values it gives me. Being it a indirect powermeter is uses some fixed assumptions which lead to a certain output, like changing my bikeposition will skew the ouput, I don't mind that as long as I have a reasonable idea of how much the influence is.
Like with this side-wind, as long as I know that with certain types of wind the reading differs a certain amount, I can can addapt too that situation and still use the data.

When I have some time I'll try to do some more testing on a fixed parcours and do it in both directions.


Greetings
Guido

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