Displayed wind is still unstable (aka incorrect)

[Zoltan]

I made a family riding with kids at extremely low speed. Bot with my road bike equipped both with a Powertap and iBike.

It was the right time to get more familiar with displayed wind speed.

After two hours of riding it was evident that my Gen3 iAero always showed a tailwind (Abs Wind was set to YES). The minimum of it was like 4-4.5 km/h, which grew sometimes upto 14-15 km/h. No headwind at all.

I did several things to be sure that there was some real problem.

0. In stationary I blew with my mouth to the wind port to see whether the sensor was "locked". No it was not, temporarily I could get a headwind of 110-120 km/h.

1. I rode ahead to be the first of the queue to avoid any tiny drafting. Tailwind remained.

2. I manually played with CdA (my height was tested between 26 and 400 cm and my weight between some 20 and 200 kg to get extremely high and low CdAs). Still tailwind was displayed always.

3. I switched between profiles to change the wind scaling. =>Tailwind.

4. I did as much as 15-20 Wind Calc during the ride (sometimes I even did with a fake blowing to the wind port with my mouth just to see how iAero reacted to this cheat)

5. I even removed iAero from the wireless mount to hold it in my hand in front of my handlebar (levelled , pointing to the direction of the ride) to see whether it shows the same Absolute Wind as my riding speed or not. My finding was that typically the displayed Wind speed was 4-5 km/h less that the riding speed, and very rarely was wind speed very close to the riding speed.

6. I repeated all of my above tests riding into some direction and the opposite direction, too.

I guess that my testing covered all the logical approaches or simply desperate ones. The only time when I got a Headwind was blowing to the wind port heavily or in case of point 5

Is there any idea what can be the reason? Can it be a software or hardware issue? Or did I forget some simple reason when I stuck into my problem?

[Zoltan]

I improved the wind scale, and was able to ride to north getting +3 - +4 km/h, while to the south getting -3 - -4km/h. So I was happy that at least in case of my trekking bike (without a DFPM) I finished with the tough part of precise setup.

Always tailwind disappeared but I got something different, which happened in the first example, but very sporadically at that time.

OK, what I got?!

I was again cruising with my family at a range of 12-17 km/h, I was the head of the eschelon. Again I used Abs Wind YES.

iBike was showing a tailwind ranging between 3 and 8 km/h, which was in line with my feelings. Suddenly iBike showed eg. -13.8km/h while the riding speed was either exactly 13.8 km/h or just a bit different. Later this fake data has disappeared. But it came again and again in real tailwind. Never in real headwind.

I also observed that sometimes pedalling or not pedalling had some correlation with this problem. Eg. I was coasting and the wind speed flawedly equalled to the riding speed, but when I started to pedal it immediately jumped to the correct -4 km/h or some. Or just the opposite, the wind speed equalled to the riding speed when cadence was like 60-70, I stopped pedalling and wind speed changed to the correct value.

I not always got this switch on and off feeling, but it happened for 15 minutes. And came back an hour later for again 10-15 minutes.
And before I forgot let me mention the very first part of the whole ride was without this strange thing (in the headwind stretch).

I start to think that either I have a defective unit or there might be some problem with the software, which is the latest fw of Gen3 iAero. I dunno, but I cant do more to finetune iBike to get a correct wind speed. I hope that displayed wind speed is a raw data measured by iBike (apart from the question of Abs Wind YES or NO) and not something which is the result of some algorithms with the purpose of improving it. Am I right?

And the ride:

2012_10_06_1105_46_km.ibr

(426.36 KiB) Downloaded 437 times

[Zoltan]

A proof using the ibr file I attached to my previous post:

Új kép (1).jpg (152.41 KiB) Viewed 5658 times

Wind speed is set to "Relative to Bike". It is zero meaning very frequently meaning that the abs wind speed, which was a tailwind equalled to bike speed.

[KenS]

I use the Newton on my trekking bike also but since I have handlebar bags and other stuff on the handlebars I use the Remote Wind Sensor.
I also did some coast downs because I figure with the extra furniture my aero profile will be non-standard.
So now I'm pretty happy that the Newton is dialled in with this setup

I only get ABS wind equal to (negative) bike speed when I can feel no wind at all so relative wind is zero. With the GenIII I'd get the same thing when there was water in the wind port. Another reason for using the Remote Wind Sensor. With the Newton it happened a couple of times before I fitted the Remote Wind Sensor but I expected it was due to the handlebar furniture.

[Zoltan]

Thanks for giving a feedback. It was useful. Having water in the unit is almost impossible, and the only difference between the equipments I had when I properly set up the unit and those in the ride on Saturday was a big pack, but behind the saddle.

There is one gadget ion my hadlebar that might cause this problem too, but it was on my bike at the time of cal ride, coastdowns, it is my Garmin 60csx. And there is a gap between my Garmin and the handlebar mount of iBike, because there is an outer helix antenna of 60csx which may influence the wind eddies around the handlebar. But it is similar to the bowden cables and the front of road bike handlebars, they also cause vortices.