Switching profile to the same profile changes result

[wellmt]

I've noticed something odd. I have a downloaded a ride from the iBike unit into the software. I can see the profile that was in the iBike at the time in the left pane/Analysis Status.

If I then use the menu item Tools->Switch Profile after the ride, and select the same profile - the result is different by about 4-5 watts. (The Aero and Fric are the same of course)

Why is this?

[racerfern]

Check in the preferences setting if you have the "Auto Fine Tune Data" checked. If so, upon initial download, the data automatically gets fine tuned. However upon switching to the same profile it's as if you have temporarily shut off the fine tuning. You would technically have to click on Analyze Power after switching profiles. That should yield the same result. Also, make sure you have the same weight in both. That can make a minor difference.

[wellmt]

No I don't have fine tuning turned on, and the total weight is the same (79.8kg)

The weird thing is, if I pick a ride done a couple of weeks ago with this same profile and switch profile to the same profile, nothing changes. If I do this to last nights ride for example, it was a couple of watts out.

[racerfern]

OK, another possibility:

Depending on your fric and aero numbers they could appear to be the same, yet be different. Both these numbers only display 3 digits to the right of the decimal point. However, Ive used the 4th digit. For example an aero of .2514 will display as .251 yet they yield ever so slightly different CdA numbers. If you were to go to .2516 the unit would display .252 but it woundn't be exactly the same as .252. You may have extracted a profile, or made a slight adjustment.

To get both back to the same, try exporting the profile on the computer to save a copy, then remove it from iB3. Now extract the profile from the ride file.

[coachboyd]

It could be that each profile also has tilt information inside of it. So on the bike when you have done your tilt calibration that info gets stored on the bike for the first five minutes and then the tilt correction goes into play.

On the software the tilt correction can happen immediately, plus if your stored tilt value is slightly different, this will also cause the watts to be slightly different. You can go to tools->analyze power and that should make it the same throughout the ride except the first five minutes could be different than what you saw on the ride.

[wellmt]

Thanks guys. Coachboyd, I think you've got it:

This profile used to match my DFPM exactly, now it does except for the first 5 mins. The question is how can I keep this profile, which is perfect but fix this problem with the tilt?

This probably relates to my other question here by the way: http://www.ibikeforum.com/viewtopic.php?f=4&t=1112

Edit: Not so sure now, I just chopped the first 5 mins from my latest ride file and then tried to apply the same profile and the figures were still out by 5 watts, so Racerfern might also have a point.

[coachboyd]

If you do the tilt calibration at the start of the ride it basically calibrates a voltage of the accelerometer (Travis explained this to me how it worked). The tilt cal number that you see in the profile is stored in the unit and it makes it so when you do a trip reset it reverts back to the original setting that is calibrated to the voltage.

Basically, if you have a spot in your garage that is -.3% and you do your tilt cal there it will use the voltage of the accelerometer to say that is -.3%. If you switch profiles to a different stored tilt calibration it could say that area is +1.6% (example). The tilt correction will kick in after 5 minutes and you'll have good results, but if you do a trip reset it will revert back to the stored voltage of the accelerometer.

I think if you do a tilt calibration before your ride, then after downloading and everything go to profiles->edit profiles. Select the profile that is in your unit, go to advanced profile settings, get tilt from iBike, then send that profile back to your iBike you should be good.

[wellmt]

Thanks again Coachboyd. I'll give it go and go from there.

[wellmt]

Forgot to say, using get tilt from iBike worked perfectly as suggested. Thanks.

[bjrmd]

Hi
Could you please review the exact steps to get the corrected tilt (after the ride is done) into the ibike so the first part of the ride is calibrated. I tried the above but there was no effect--first part of ride was still off calibration.

[wellmt]

I did this*

1. Make sure the profile you want is in the iBike and selected
2. Do a tilt calibration
3. Do a wind calibration
4. Go and ride your bike as normal
5. Download the ride in iBike3
6. Go into Profiles->Edit profiles. Select the profile that is in your unit, go to advanced profile settings, press the "get tilt from iBike" button. Save the profile. (It's not possible to tell anything has changed since the values won't alter)
7. Using iBike3, send that updated profile back to your iBike.

The next ride your data should be good in the first 5 minutes too.

* my memory is rubbish so this may not entirely be correct and I don't have the software to hand.

[coachboyd]

Hi
Could you please review the exact steps to get the corrected tilt (after the ride is done) into the ibike so the first part of the ride is calibrated. I tried the above but there was no effect--first part of ride was still off calibration.

All you should have to do is a tilt calibration before you ride.

I usually do about 1 tilt calibration per week.

[wellmt]

Coachboyd is right of course. That will fix the tilt problem.

The problem will still reoccur if you send a happen to send the profile from the software back to your iBike again, unless you update the profile stored in the software with the procedure above (or you do another tilt cal).