Mid-Ride Wind Cal with RWS

[pjboyle]

Would it be considered acceptable to seal off the inlet end of the RWS lightly with a finger tip to do a Wind Cal at a mid-ride stop? This time of year we can get fairly large temperature gains during a morning or late afternoon ride of a couple of hours and if I think of it I will sometimes do a wind cal. I know it is discouraged to directly seal off the wind sensor port on the head unit, but it would seem to me that the RWS adds enough volume to the system that putting a finger over it in this way would have negligible effect on the pressure of the trapped air.

PJBoyle

[racerfern]

I still wouldn't seal it off. I think you should cup your hand closely around the opening and hit the center button.

[Russ]

The little hole underneath behind the wind port is part of the deal. So the objective, I think, would be to let the pressure equalize between the two, so sealing off one defeats the purpose.

Someone suggested, I think it was, a freezer bag that crunches up in the pocket to nearly nothing. I use a zip lock and hold it over the whole ibike assembly while zeroing wind.

I think the bag idea is superior to the cupping if it is windy but cupping is the current Velocomp official recommendation.

Russ

[pjboyle]

I understand the reasons for not pressing a finger into the wind port directly on the iBike. It is sensitive enough and the volume of trapped air is small enough that you could inadvertently create a small amount of pressure that the sensor would read during the cal button press. Early on the Velocomp video on how to calibrate it showed the hand cup method for this. Later this was disavowed as in windy conditions the cupped hand can either direct wind into the port or create other anomalies at the mouth of the port (turbulence). I also prefer the plastic bag method if in a pinch out on the road (sometimes I have ot eat my fig newtons early if I need to do a cal!). Better is inside the car or garage prior to starting out.

I think the RWS is a different case as the system air volume is increased by a huge factor when you add that tubing, and gently covering the end with your finger tip should have really neglible effect on pressure, since you can't make a significant change to the trapped air volume. Thanks for the answers. I was just curious to see if Velocomp would endorse this method. I've been doing it when the need arises and seen no ill effect. I prefer it to the cupping method and I don't always have a bag handy.

PJBoyle

[racerfern]

The little hole underneath behind the wind port is part of the deal.

IIRC, the little hole underneath has nothing to do with wind scaling or wind offset. I believe this is how the barometric sensor measures barometric pressure to determine altitude.

It's easy enough to put the RWS on in your house and zero the offset. Then cover the end with your finger and see if the offset changes. On my system with a RWS tube about 12 inches long the offset changes dramatically one second after I put my index finger over the end. It goes from zero to over 45. Perhaps covering with a porous cloth would work.

[Velocomp]

We recommend against blocking the wind port by placing any finger on the port's surface, whether the port itself or the funnel of the RWS.

Blocking the wind port will create additional pressure in the wind port cavity, causing the wind sensor to detect a false zero reading.

In fact, experienced iBike owners may notice that holding the Cal Wind center button for too long will cause a non-zero result. That's because the force of your fing, held on the center button, will pressurize the iBike's innards a little bit.

It's that sensitive!

When I'm outdoors and in windy conditions I will cup my hand carefully over the wind port (or the RWS). I'll try to get out of the wind as much as possible; if I can't do that then I will face in to the wind, which minimizes the possibility of my hand acting as a wind scoop.

The small hole at the bottom is for barometric pressure readings. This is how the iBike measures elevation changes.