Wind Calibration Question

[rcmaps]

Hi, I'm a new ibike user with the latest firmware. Apologies if this has been asked before but I have searched here and read the manuals a few times but have not been able to find the answer.

It is recommended that before going out on a ride, to do a wind calibration and also to acclimatise the unit to outdoor temperature first before doing so.

How long should the unit be placed outside to acclimatise? 1 minute, 5 minutes or 10 minutes?

What is the point of acclimatising?

Secondly, could someone please explain the point of doing a wind calibration each time?

I normally perform this in the garage before pushing the bike outdoors and do it multiple times until I get 0.0 or as close as possible to this value. Should I leave the unit outside to acclimatise, put it onto the bike outdoors then do a wind calibration?

Thanks for your reply.

[dtrousdale]

How long should the unit be placed outside to acclimatise? 1 minute, 5 minutes or 10 minutes?

What is the point of acclimatising?

Secondly, could someone please explain the point of doing a wind calibration each time?

To the best of my knowledge, here are the answers to your questions:
1. 5 minutes
2. to get the temperature inside and outside the unit the same
3. because the temperature changes

[racerfern]

I shy away from using the words wind calibration. Calibration is done as part of the cal ride.

What you're doing each time before the ride is setting the wind offset which is just like setting the tare weight on a scale; zeroing it out. Wind offset is affected by weather conditions such as temperature and barometric pressure. Wind offset can also be affected by battery voltage, so a unit that just had the battery changed will display a different wind offset than an old battery everything else being equal. So doing a wind offset is like setting the elevation prior to starting a ride, it's something that should be part of your preparation process. At least it's part of my ritual.

Depending on where you live, the temperature change from inside your house to outside can be radical. That's why you put the unit outside to adjust. I live in an area with very strong sun so I see the temperature of the unit rise substantially as the day progresses. When this happens, I take the time to do another wind offset at some point along the ride. With a little vigilance you'll have reliable data and you won't be second guessing yourself or the iBike.

FYI, if during a ride I switch to the wind offset screen and see a number in the +/-3 range, I do a wind offset. If I see a number in the +/-1 range I don't even bother, I just exit the offset screen since that amount is really small.

Sorry for the long winded post but hopefully this will clear up questions about needing to do wind offsets.

[rcmaps]

Thanks racerfern and dtrousdale for the clarification.

I did not realise that temperature itself affects the wind offset. I thought the unit just measures wind speed and using the analogy of a simple thermometer measuring temperature, one wouldn't need to offset/calibrate a thermometer everytime before using it. Obviously, wind measurement is different.

If what you are suggesting is correct, ie barometric pressure also affecting wind offset and hence power readings, then presumably, it is also crucial to re-adjust the elevation prior to every ride - especially during pressure changes overnight etc. I know exactly the elevation of my house based on GPS and topo map readings, and I try to make it a point to reset this prior to the ride correctly if I'm not in too much of a hurry. One does have to perform many button presses to alter altimeter settings unlike my previous Sigma Rox9 which I can store 2 known elevation settings and just need to press two buttons simultaneously for 2 seconds to correct the current altimeter.

I'm surprised that battery voltage also affects this! We are getting into colder weather now and I have noticed that battery life can shorten considerably in colder weather. Hence I guess, frequent battery changes is also important if it drops below 2.7V or 2.8V.

I shall have to remember to leave the iBike unit outside for at least 5 minutes before going out each time.

[lo-daddy]

So doing a wind offset is like setting the elevation prior to starting a ride, it's something that should be part of your preparation process.

I had no idea I was supposed to be setting the elevation prior to every ride.

[Avanti]

Same goes, how critical is that step? I mean I know temp, has a bearing I see my offset sometimes at -12 after 15 mins into a cold ride...But Elevation, can someone explain this one for us?

[racerfern]

I'm not saying you HAVE TO set the elevation. I'm saying I do as a habit. With the latest version of iBike software you have the option to enter starting and elevations if known, so for me I go out of my way to get it right. It's not like it takes too much time.

[Avanti]

I'm not saying you HAVE TO set the elevation. I'm saying I do as a habit. With the latest version of iBike software you have the option to enter starting and elevations if known, so for me I go out of my way to get it right. It's not like it takes too much time.

Hi Fernando,

Yep I get that, but as a matter of performance or data intergrity, how critical is this step?

[racerfern]

I don't believe it actually plays into equations as you ride, it may get used in post-ride analysis however. I'll let Velocomp tell us for sure.

[rruff]

The pressure sensor is measuring dynamic pressure directly, and air density is a part of this term. This value multiplied by CdA gives you the power to overcome aero drag. To determine the wind speed, the firmware must make some assumptions about air density... which will depend on barometric pressure (measured) and temperature (measured), and humidity (not measured, but a small effect). Unless I'm missing something, an incorrect elevation would create no issues with any part of the data except the elevation itself.

[coachboyd]

correct, if your elevation is off on the iBike then the only thing it will effect is your altitude numbers (nothing with power). Your elevation profile will still be correct as will the feet of climbing, it's just when you look at the high point of your ride that number can be off.

If you are doing a ride where you finish on top of a climb of known elevation, then you may want to set the correct elevation at the start of your ride.

[rcmaps]

How long should the unit be placed outside to acclimatise? 1 minute, 5 minutes or 10 minutes?

What is the point of acclimatising?

Secondly, could someone please explain the point of doing a wind calibration each time?

To the best of my knowledge, here are the answers to your questions:
1. 5 minutes
2. to get the temperature inside and outside the unit the same
3. because the temperature changes

Actually, today I re-read all the ibike pdf documentation and in the software manual, it suggests to :-

"ride around for 10 minutes to acclimatise the ibike before doing wind calibration..."

I probably missed this the first time around as it was a heck of a lot of info to digest as a new user!

[rcmaps]

What you're doing each time before the ride is setting the wind offset which is just like setting the tare weight on a scale; zeroing it out. Wind offset is affected by weather conditions such as temperature and barometric pressure. ...
Depending on where you live, the temperature change from inside your house to outside can be radical. That's why you put the unit outside to adjust.
FYI, if during a ride I switch to the wind offset screen and see a number in the +/-3 range, I do a wind offset. If I see a number in the +/-1 range I don't even bother, I just exit the offset screen since that amount is really small.

We're into winter now in this country. On my daily commute home from work, I have the unit in the office at 24 deg C, put the unit on my bike and wheel it outside into something like 10 -14 deg C. It's not practical to leave the unit outside for 10 mins to acclimatise in this situation. Don't fancy sitting outside for 10 mins doing nothing in 10 deg C just to do a wind calibration!

Once I get home, I do a wind offset check and noticed that the offset was -4 today, the wind and temperature was relatively similar - well maybe 1 or 2 degree colder.

So the question I have is that when I download the ride, can I simply post process the data by performing "Analyze Wind" and set the "Offset Wind" by -4 in this case?

I realise it's not perfect but theoretically if ambient conditions are identical at start and end points, will this have the same effect as leaving the iBike outside to acclimatise for 10 mins before doing the wind offset prior to the ride?

Actually, I noticed by doing this, the wattage goes up to something more resembling the perceived effort but I'm unsure as I'm still new to this.

Thanks.

[racerfern]

I realise it's not perfect but theoretically if ambient conditions are identical at start and end points, will this have the same effect as leaving the iBike outside to acclimatise for 10 mins before doing the wind offset prior to the ride?

This should work OK, however it will become an issue if you're shooting for a certain wattage range during your ride since your numbers won't really be in range.

[rcmaps]

I realise it's not perfect but theoretically if ambient conditions are identical at start and end points, will this have the same effect as leaving the iBike outside to acclimatise for 10 mins before doing the wind offset prior to the ride?

This should work OK, however it will become an issue if you're shooting for a certain wattage range during your ride since your numbers won't really be in range.

Thanks racerfern.

That shouldn't be a problem as I'm not usually in training at the time and hence aiming for a target wattage zone.

[rruff]

So the question I have is that when I download the ride, can I simply post process the data by performing "Analyze Wind" and set the "Offset Wind" by -4 in this case?

I'd check to see if this is consistent... a change of -4 is pretty big for a 10-14C temperature drop.

[Avanti]

I realise it's not perfect but theoretically if ambient conditions are identical at start and end points, will this have the same effect as leaving the iBike outside to acclimatise for 10 mins before doing the wind offset prior to the ride?

This should work OK, however it will become an issue if you're shooting for a certain wattage range during your ride since your numbers won't really be in range.

Hi Fernando,

Just to take your point further. During a training ride with intervals last night I had an instance where I did the original zero offset, rode for about 15 mins checked the offset it was around - 4 so I did another offset all good and just before starting my intervals checked to make sure the offset was still ok and it was fine. Went about doing all the intervals and got some good results.
When I look at my original avg wattage its showing 262 watts for the session and when I check the analyze wind function its showing an avg ground wind of 8.4, now from what I understand if your ride is an out and back the wind offset should be close enough to zero correct? If I do this my avg drops about 80 watts out, this I actually believe to be correct...The issue though is that when I'm doing the interval I'm seeing these great numbers come up which actually afterwards aren't so great. How do I make it more accurate?

[rruff]

If the wind was consistent and your wind offset was zeroed, then your wind scaling is way off.

[racerfern]

Using your example, an average wind ground speed of 8.4 is massive. So, if this was more or less an out/back ride your wind offset was completely off or as rruff suggests, your wind scaling is way off. I assume it's your wind offset since you've got quite a few rides under your belt.

For my rides my post analysis is always within a couple of watts and I don't have any checked boxes. I input my starting and ending elevation since it can drift with barometric changes and that's it. Nothing other than error is going to magically add or remove 80 watts from a ride. You know what your numbers feel like so if the 80w lower makes sense then something's wrong in your setup for this ride and yes, 8.4mph can cause that kind of error.

[Avanti]

Using your example, an average wind ground speed of 8.4 is massive. So, if this was more or less an out/back ride your wind offset was completely off or as rruff suggests, your wind scaling is way off. I assume it's your wind offset since you've got quite a few rides under your belt.

For my rides my post analysis is always within a couple of watts and I don't have any checked boxes. I input my starting and ending elevation since it can drift with barometric changes and that's it. Nothing other than error is going to magically add or remove 80 watts from a ride. You know what your numbers feel like so if the 80w lower makes sense then something's wrong in your setup for this ride and yes, 8.4mph can cause that kind of error.

Sorry I should of put 8.4kmh, as we do things different here in the land of Oz. This equals 4mph, I'm still really struggling with this. My profile seemed all good for the last few months perceived effort as well as wattages were lining up and I was happy.
Now and I'm not sure if it's the on-set of winter here but my numbers whilst training just don't match after I have downloaded and analyzed. This morning once again on an out and back ride I was sitting in my endurance zones around 200 - 240 w. I did an offset before I went out and then again 10 mins into ride, it was a cold morning here 40 F.
My original download states 204.7 avg watts, after I analyze it as the ride finishing where it began I get 158 avg watts. This is really killing my training and making me second guess the unit constantly.
Looking at the original download I know it's not correct it pretty much has me going into a head wind the entire ride which was not the case and especially not so on an out and back ride. What I'm after is whats happened, the unit was working brilliantly I have not moved it or the handlebars, my position or gear havent changed. The only thing I can think of is temp as when I did my cal ride initially we were in summer and temp was 90F now being 40F on most mornings is this the reason?
Hoping you can help me here Fernando as you seem to be all over the behaviour of these units.

[rcmaps]

Hi Avanti
I've been having similar issues to you to lately as we get into colder weather.
Everyday last week I've been riding in somewhere between 0 - 5 deg C in the mornings.
I've left the unit outside for about 20mins to acclimatise, put it on my bike and do a wind offset.
While riding I've noticed very low power readings compared to what I experince normally. The avg for the ride on the unit is rather low. Later in the evening after downloading it and "analysing ride", the avg shoots up markedly representing a more realistic level based on my past experience riding the same route is warmer temperatures with similar wind conditions.
I'm wondering whether it's the cold weather playing havoc on the battery during the ride although I've replaced the battery recently (probably less than 10 hrs usage). On start up each time, it reports that Battery is good though.
I guess it's just something that we'll have to live through over winter months.

[Avanti]

Hi Avanti
I've been having similar issues to you to lately as we get into colder weather.
Everyday last week I've been riding in somewhere between 0 - 5 deg C in the mornings.
I've left the unit outside for about 20mins to acclimatise, put it on my bike and do a wind offset.
While riding I've noticed very low power readings compared to what I experince normally. The avg for the ride on the unit is rather low. Later in the evening after downloading it and "analysing ride", the avg shoots up markedly representing a more realistic level based on my past experience riding the same route is warmer temperatures with similar wind conditions.
I'm wondering whether it's the cold weather playing havoc on the battery during the ride although I've replaced the battery recently (probably less than 10 hrs usage). On start up each time, it reports that Battery is good though.
I guess it's just something that we'll have to live through over winter months.

Hi RC,

Interesting yours does the exact opposite that mine is, as mine is constantly over-reporting watts on the actual unit and yes my battery as well can start the ride with around 290 volts and 30 mins later be sitting on 260.

I'd imagine New Zealands weather would be very similar to Australia with it's extreme nature and I think we may of answered the question.

[Avanti]

So a question for Velocomp, if the temp variance is indeed the issue here. What can be done in the profile to adjust for a 'winter profile', I know there was talk some time ago about a guide coming out explaining step by step how to adjust profiles. Is this still in the design phase? If not is there anything I can do to correct my profile in cold weather?

[Velocomp]

Please post a ride file.

[Avanti]

I posted yesterday mornings ride file on the earlier post, cheers John.