Effect of Cross Winds

[ldmitruk]

Hi,

in post http://www.ibikeforum.com/viewtopic.php ... wind#p5115 R Mc mentions iAero's can under report when riding in cross winds. I was out last night on an east west out and back ride with constant north cross wind on a fairly level road. I noticed my power levels seemed low compared to the amount of effort I was putting in. Is there a way to compensate for the low power reading in these situations? I'll try to post screen shot of the data later today.

Cheers!

[ldmitruk]

Hi,
Here's some screen captures.

First up show the wind direction as determined using Sports Tracks

WindDirection.jpg (99.09 KiB) Viewed 5853 times

Here's the wind analysis from my iBike Aero which looks O.K. to me.

WindAnalysis.jpg (149.79 KiB) Viewed 5852 times

And a detail of an 3 minute interval

poweranalysis.jpg (100.47 KiB) Viewed 5853 times

What it felt like was happening was the amount effort I was exerting was going up as I maintained my speed but the wattage was not following suit, in fact the wattage seemed to be decreasing more than it should have. So is an expected effect from a strong crosswind?

Cheers!

[roadrash]

How did you actually feel at the end of the ride? More or less fatigued than usual?

I went on a 20 mile trip out and back last week with a 15-20 mph, 90 degree constant crosswind the entire ride. I'll have to say that even though the overall effort seemed greater, I was really no more fatigued when I got back than usual. I wonder if it's because the added effort was in negotiating the cross wind (keeping my bike on the shoulder, managing gusts, etc.), not in extra power to the pedals. If you think about a sailboat traveling perpendicular to the wind, the wind actually makes it go faster than any other orientation to the wind. I wonder if the same principles somehow holds for a biker riding perpendicular to the wind. This is a totally novice guess and I may very likely be completely wrong, but I'm such a newby at this that I don't mind having my idea shot down quickly by those who know much more than I do.

Thanks for sharing your experience. I look forward to seeing what others think.

Cheers

[ldmitruk]

It wasn't so much the end of the ride, but the effort during the intervals. For maintaining a average wattage of less than 200 watts for 3 minutes I was really bagged at the end of each interval. That being said, I did feel that I had worked very hard at the end of the ride. And looking at the relation of the amount of wind to the amount of power it appears to me the wind is increasing while the wheel speed is fairly steady.

[rruff]

Unless the wind shifted radically, then the iBike was obviously under-reporting your wind speed. Are you using the latest firmware? When was the last time you checked your wind scaling?

[Russ]

If this winds up a double post, sorry. I tried to post this observation about the time rruf posted and it seems mine got eaten by the bit bucket.

I see a variation of wind direction recorded of from 340 to 043 with 017 being the average.
Thus I would expect, since your direction of travel was due E/W at least an occasional head wind.
Since I NEVER see even an occasional head wind, this makes me suspect your wind offset or calibration or both.

Regards,
Russ

[ldmitruk]

The average wind direction is a bit deceiving. I checked along the full course and the wind was mainly from the north. In terms of firm ware the unit has 3.10 and I set the offset just before I started the ride. I'm beginning to think I might have to redo my coast downs.

[rruff]

If your wind scaling is off, then you need to redo the cal ride. Coastdowns would not be necessary.