Average Ground Wind Effect

[5am]

Something that's been on my mind since the introduction of ibike 2.0 software is the "average ground wind" figure when I analyze a ride file. On a ride yesterday, for example, the wind was blowing steady 10-13 mph with periodic gusts to 19 mph from WNW and swinging to NNW. My ride was along an out and back route generally running westward outbound and eastward inbound. Classic strong headwind out and tailwind back though the wind was much reduced by the time I made my turn for the inbound portion and it didn't feel like much of a tailwind (though that is often hard to gauge).

On download and analysis, the avg. ground wind was shown as -1.1 (with a wind offset figure of 0.0). Can someone explain how this -1.1 figure was derived? and what relation does it have to the wind offset? (Changing one figure in the window appears to affect the other.) Is it simply headwind - tailwind? (Presumably, the figure would be close to 0 assuming given my west/east route so I'm not entirely sure why I'd get a negative figure.) Changing the ground figure even to as little as +1 in the avg. ground wind window (a change of +1.9, which also changes the wind offset figure to -1.1) has a BIG effect on the overall aero figure in the power calculation - about an 11% increase in the power average for the ride. And of course, if I were to change the avg. ground wind figure to close to the actual average wind I experienced outbound (say a steady 11 mph for argument's sake), my overall power average figure for the ride jumps 70%+.

In any case, I'm not all certain now what the avg. ground wind figure is telling me or how I should consider it and (because there's window allowing me to change the figure) when and under what circumstances I might want to change either ground wind or wind offset figures in analyzing a ride file. As always, any help appreciated.

[5am]

Anybody?

[racerfern]

Two things:

#1: When I clicked on the forum at 7:25 Sunday morning, this message was listed as new since my last visit. However you posted this message a couple of days ago and I have been on a number of times since then. Admin should check this out.

#2: Were you on a road with constant traffic? Was the wind really more of a cross-wind? More importantly; Was the ride alone or were you riding with someone else? And finally; Under what conditions did you set your wind offset? Final question; Have you done this ride before and if so how did the power output compare to other times with similar conditions?

[5am]

Two things:

#1: When I clicked on the forum at 7:25 Sunday morning, this message was listed as new since my last visit. However you posted this message a couple of days ago and I have been on a number of times since then. Admin should check this out.

#2: Were you on a road with constant traffic? Was the wind really more of a cross-wind? More importantly; Was the ride alone or were you riding with someone else? And finally; Under what conditions did you set your wind offset? Final question; Have you done this ride before and if so how did the power output compare to other times with similar conditions?

Let's see. I was on both road and paved bike trail. Probably 60% trail and 40% road. Traffic was pretty spare on the roads. Ride was solo. Wind offset was set to 0 before the ride as per my usual pre-ride ibike preparation. I've done this ride many, many times before and the power output versus similar rides was hard to judge because of the old winter bugaboo with the ibike. Temps were in the low 40's, high 30's and after 30 minutes or so my readings became pretty low and stayed that way although for a winter ride the final average reading was pretty typical. Running the ride file through post ride analysis in ibike software didn't raise the the overall power average much more than a few points

[gray8110]

#1: When I clicked on the forum at 7:25 Sunday morning, this message was listed as new since my last visit. However you posted this message a couple of days ago and I have been on a number of times since then. Admin should check this out.

I'm missing something here - 5am had a second post at 7:49 PST Saturday evening - which would make this a new post to you unless you had visited and read this post between then and Sunday morning.

Just a clarification regarding the forum icons - the red topic icon -- -- indicates an unread post. The forum cache resets periodically, but generally, if you haven't read a post, that icon will be shown. These aren't just entries since your last visit, they are unread posts. It is also worth pointing out that this information is stored in cookies on your local machine so if you have cookies disabled or reset them occasionally, the unread post data may be inaccurate.

[racerfern]

I'm missing something here - 5am had a second post at 7:49 PST Saturday evening - which would make this a new post to you unless you had visited and read this post between then and Sunday morning.

I mean the first post, not the post that said "Anybody". I was on numerous times on Friday and the first post did not show (at least for me) until the second post that said "Anybody?" showed up almost 24 hours later.

As far as the ground wind... I too have seen numbers that tend to be negative even though I'm convinced I zeroed out correctly and I rode out and back. It seems that the headwind direction numbers (riding alone) tend to fluctuate down a lot more than the equivalent tailwind numbers tend to fluctuate up. In my case these last few weeks have seen huge temperate, wind and barometric changes in SoCal and this may have a lot to do with it. I wish I had more to contribute other than confirming.

[gray8110]

I mean the first post, not the post that said "Anybody". I was on numerous times on Friday and the first post did not show (at least for me) until the second post that said "Anybody?" showed up almost 24 hours later.

Wow! That is an almost unverifiable problem - by that, I mean it will be very difficult to troubleshoot. I looked at the forum database, the topic was posted at 9:19pm server time and had multiple views that evening. I can also see that the post was sent to my RSS reader at 10:19 PST and I marked the post as read in the RSS reader the next morning. I'll keep an eye out for posts that aren't appearing but it is hard to recognize a problem in these cases.

[travispape]

Something that's been on my mind since the introduction of ibike 2.0 software is the "average ground wind" figure when I analyze a ride file. On a ride yesterday, for example, the wind was blowing steady 10-13 mph with periodic gusts to 19 mph from WNW and swinging to NNW. My ride was along an out and back route generally running westward outbound and eastward inbound. Classic strong headwind out and tailwind back though the wind was much reduced by the time I made my turn for the inbound portion and it didn't feel like much of a tailwind (though that is often hard to gauge).

On download and analysis, the avg. ground wind was shown as -1.1 (with a wind offset figure of 0.0). Can someone explain how this -1.1 figure was derived? and what relation does it have to the wind offset? (Changing one figure in the window appears to affect the other.) Is it simply headwind - tailwind? (Presumably, the figure would be close to 0 assuming given my west/east route so I'm not entirely sure why I'd get a negative figure.) Changing the ground figure even to as little as +1 in the avg. ground wind window (a change of +1.9, which also changes the wind offset figure to -1.1) has a BIG effect on the overall aero figure in the power calculation - about an 11% increase in the power average for the ride. And of course, if I were to change the avg. ground wind figure to close to the actual average wind I experienced outbound (say a steady 11 mph for argument's sake), my overall power average figure for the ride jumps 70%+.

In any case, I'm not all certain now what the avg. ground wind figure is telling me or how I should consider it and (because there's window allowing me to change the figure) when and under what circumstances I might want to change either ground wind or wind offset figures in analyzing a ride file. As always, any help appreciated.

Sorry for the delay in the reply--almost all of us iBike folk had a really busy (& good) weekend.

For clarification...what you see on the iBike unit while on the road (for now) is the wind speed relative to the bike. If you ride 15 mph on a calm day, you will see a 15 mph reading on the unit. You probably already know this, but just in case.

What you see in the wind analysis window is distance-based-average wind speed minus the distance-based-average wheel speed. What that -1.1 indicates that you data was showing a 1.1 mph tailwind along the direction of your travel. (If you had a crosswind, the net wind would have been something higher than 1.1.)

By doing a distance-based average rather than a time-based average, as long as the wind conditions stay uniform during the course of the ride and the ride is an out-and-back, then the average that you should get in that box is 0 or very close to it. The distance-based average takes into account that you spend more time riding into the headwind.

So given the fact that you did an out-and-back ride and that the perception was that the wind was dying when you had the tail wind, the conservative thing for you to do would be to set that number to 0. If you want take advantage of the obervation that the wind was dying (maybe you could verify this first by looking at your weather history at weatherunderground.com), then you could set the number to something slightly larger than 0--say about 0.5 mph. That would reflect a net 0.5 mph headwind for the whole trip. (And when looking at airport wind readings remember that the wind at road level is something less than the airport reading which is much higher off the ground and away from all the trees.)

(By the way, the most likely reason that you have to make any adjustment to your wind offset is because your iBike probably wasn't cooled down to riding temperature at the time you did your wind offset. We are looking at ways to address this issue in the future.)

A couple more things to keep in mind: If you ride in a draft, then you would expect to see a negative number in the wind analysis window. Also, if your ride ends in a different place than where you began then you would not expect the distance-based-average wind to be 0.

Travis

[5am]

Thanks Travis.