Wind Callibration

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Rick
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Joined: Mon Jul 02, 2012 7:42 am

Wind Callibration

Post by Rick »

Will someone please clue me into the proper protocol for and significance of wind calibration. i have followed the meager instructions and am frustrated that weird wind factors have been radically skewing my power results. Thank you!
KenS
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Re: Wind Callibration

Post by KenS »

You may need to clarify whether by "wind calibration" you mean the Wind Cal option in Newton setup or the Cal ride
If you've done a proper Cal ride you should not be getting weird wind factors.
That includes letting Newton settle to ambient temperature then do a Wind Cal in a sheltered location with no wind.
You only need to do a subsequent Wind Cal if the temperature has changed a lot since the last one.

Might be worth posting a ride file here that illustrates the skewed results you are getting for the gurus to look at.
-- Ken
JulianBoulter
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Re: Wind Callibration

Post by JulianBoulter »

Hi guys,

Don't know if this was ever answered so reviving the thread. I understand that a wind cal should rarely be performed but I would like to understand how to do one anyway.

What am I looking for as the numbers change and what is it actually doing? i.e. is it applying the wind scaling factor from the profile or is it actually calculating a new wind scaling factor on the fly?

Thanks

Julian
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Russ
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Re: Wind Callibration

Post by Russ »

Hello JulianBoulter,

The wind cal function sets or calibrates the wind sensor to zero (or near zero) during a no wind condition.
A large temperature change may cause a drift in that calibration. It is not necessary for it to settle exactly on zero. You should also give it a little time to settle. I usually cup my hand over the port even if inside due to the high sensitivity to slight drafts.

I usually don't even bother with doing a wind cal for a large temp change, this time of year (spring/fall) but maybe once in winter and once in summer (maybe a bit more). But I use Issac route/wind cal functions on most rides to correct any shift. I guess my point is that even a 20 degree swing doesn't (on my unit) cause a large power difference.

Of course if you are going out on a new cal ride, you need to do both a tilt and wind cal before hand close to the time of the cal ride.

Regards,
Russ
JulianBoulter
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Re: Wind Callibration

Post by JulianBoulter »

Great, got it. Thanks As always Russ
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racerfern
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Re: Wind Callibration

Post by racerfern »

Hey Julian,

There are actually two "wind" settings.
1) Wind scaling: Is the average wind between riding into a headwind and riding along in the same wind but as a tailwind. Obviously the wind has to "flow" around your body in both directions. Wind scaling is established on a cal ride and "zeros" out the wind as you do an out/back. It is best to do this when the wind is nearly as calm as possible so gusts don't skew the results. If I have to do a cal ride to create a new profile I do it before 5AM before the winds pick up in my neck of the woods.

2) Wind offset is the change in wind "pressure" based on temp, humidity, elevation, etc. Nowadays, this is almost automatic and as Russ said you only have to zero out the wind offset a couple of times a year at the most. I live in a relatively mild climate and I haven't done a zeroing for a wind offset in almost a year. I just get on and ride. People who obsess over the wind offset are actually making their Newton re-learn things. "Clip in and ride" is my motto.
Fernando
JulianBoulter
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Re: Wind Callibration

Post by JulianBoulter »

Thanks Fernando
racerfern wrote: Wind scaling is established on a cal ride and "zeros" out the wind as you do an out/back
Can we explore this a bit further, by zero you mean establish an offset right? I always though wind scaling was about calibrating the wind sensor based on the Newton's location on the bike but are we saying that it is related to the riders position and particular clothing too? i.e. the wind's affect on the rider?
Velocomp
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Re: Wind Callibration

Post by Velocomp »

The Cal Ride is used to calibrate the tilt sensor and the wind sensor.

The tilt sensor is calibrated by comparing the readings of the elevation sensor to the accelerometer. On an out and back ride both sensors should record the same slopes. The "tilt offset" adjusts the accelerometer reading so that this condition is true.

The wind sensor is calibrated by comparing the readings of the speed sensor and the wind sensor. On an out and back ride, the average wind speed should equal the average bike speed. The "wind scaling factor" (not the wind offset) is adjusted so that this condition is true.
John Hamann
JulianBoulter
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Re: Wind Callibration

Post by JulianBoulter »

Thanks John, I guess what i would like to understand is why is wind scaling even necessary given factory calibration? i.e is it establishing the wind specific to the position of the Newton on a given bike, is it calibrating the speed sensor against a particular speed sensor necessary due to sensor variation? etc. I read a post somewhere that suggested that the wind scaling is affected by things like an aero helmet, so is it related to the aerodynamics of the rider?
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Russ
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Re: Wind Callibration

Post by Russ »

JulianBoulter,

I can answer this one for John. The windscaling is needed because the pressure of air that the wind port 'sees' from where it is mounted on the bike is quite variable. You have probably seen a picture of something in a wind tunnel with smoke injected to show the air flow. The envelope of air flow shape is different for every setup and position, the position of the iBike in that envelope makes it's actual pressure reading have an offset from 'pure air' flow. Think of ten feet out in front of the bike where the air is doing it's own thing then as the bike arrives at the section of air, for example, it is probably compressed somewhat in the flow. So perhaps this picture will make clear the need for a correction factor that the factory can not possibly foretell.

This is why the remote wind sensor is helpful for time trial bike setups. It is used to place the sampling port out in front of the area where the hands are changing the envelope shape.

Russ
JulianBoulter
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Re: Wind Callibration

Post by JulianBoulter »

Thanks Russ, this is exactly the kind of background I was looking for, is it possible to use this information in the calculation of Cda at all?

On the subject of the RWS I have just installed one on my race bike with clip on tri bars. The idea is to keep the Newton on the stem but plugged into the RWS and to create 2 profiles, one with the clip ons and one without, will let you know how I get on.

Cheers

Julian
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Russ
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Re: Wind Callibration

Post by Russ »

Hi JulianBoulter,

You are welcome, far as it went :=)
As to "is it possible to use this information in the calculation of Cda at all?"
If you mean by 'this' as the windscaling values, I am sure the layman's answer is no and probably Velocomp can't either :-)
So keep in mind that with the aero bar profile and the other, keep apples to apples , so to speak. Only work with one setup and profile at a time for any dynamic CdA comparisons, the variable may just keep adding up!

Russ
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