Erroneous power readings on Ibike

[aytchkay]

I've done several coast-downs & 4 mile rides to calibrate my Ibike. I perform tilt & wind calibrations AFTER my Ibike has reached riding temp. Two things are weird: (1) no matter how many times I set my starting elevation, it is always something different the next time I use it; (2) the power readings during my ride are about 100 watts higher than what I think they should be. I recently tested on a Computrainer to get my sustained power over 40 mins, at LT, so I have an idea of what I'm putting out.
Yet, when I analyze in the Ibike 2 software, after clicking thru various adjustments, it does finally adjust to what I believe, is the actual average power, etc., for the particular ride. But I would like to see my 'real' power on the Ibike.

I'm sure my mount is pretty tight and level - It is attached to one aero-bar using an 'accessory bar' from Profile Design, with a glued-on section of PVC pipe to equal the diameter of the mount. My bike is a carbon Kestrel Talon and I weigh 153#.

My Cda (0.334)and Crr (0.00192) don't quite come out as predicted in the manual for Ibike 2 software. I'm using firmware 1.16.

Any suggestions how to 'fine tune' my unit so I can finally just ride & train....I'm starting to get a bit frustrated with the setup after 2 months.

thanks,
howard
in Chicago

[iodaniell]

Elevation will change with the weather since the device uses a barometer. You will need to find out your elevation, and set it each time, along with the tilt and the wind offset.

Without seeing your power files (I'm sure Travis or Richard will likely ask for it to give you a definitive answer), I'd guess that perhaps you are getting a little bit of upward flex out of your aero bars, making the data look like you're climbing or your roads are causing accelerometer overload. If you did your CDs and long ride, these are the likely sources of error for that amount of excess wattage--but, I'll defer to Richard and Travis.

[travispape]

I've done several coast-downs & 4 mile rides to calibrate my Ibike. I perform tilt & wind calibrations AFTER my Ibike has reached riding temp. Two things are weird: (1) no matter how many times I set my starting elevation, it is always something different the next time I use it; (2) the power readings during my ride are about 100 watts higher than what I think they should be. I recently tested on a Computrainer to get my sustained power over 40 mins, at LT, so I have an idea of what I'm putting out.
Yet, when I analyze in the Ibike 2 software, after clicking thru various adjustments, it does finally adjust to what I believe, is the actual average power, etc., for the particular ride. But I would like to see my 'real' power on the Ibike.

I'm sure my mount is pretty tight and level - It is attached to one aero-bar using an 'accessory bar' from Profile Design, with a glued-on section of PVC pipe to equal the diameter of the mount. My bike is a carbon Kestrel Talon and I weigh 153#.

My Cda (0.334)and Crr (0.00192) don't quite come out as predicted in the manual for Ibike 2 software. I'm using firmware 1.16.

Any suggestions how to 'fine tune' my unit so I can finally just ride & train....I'm starting to get a bit frustrated with the setup after 2 months.

thanks,
howard
in Chicago

Like Isaias already mentioned, all altimeters require regular calibrations since they use the atmospheric pressure to determine elevation.

Also, I think Isaias probably already figured out the issue with your power readings, but if you send me a couple of your ride files I'll look into it: travispape at yahoo.

[aytchkay]

I'd guess that perhaps you are getting a little bit of upward flex out of your aero bars, making the data look like you're climbing or your roads are causing accelerometer overload. If you did your CDs and long ride, these are the likely sources of error for that amount of excess wattage--

I have not been using the aero bars while using & calibrating the Ibike....I'll send ride files...

thanks for your rapid response...

howard

[davidpuglia]

I would suggest not attaching your iBike to the Aero Bar - I tried that once and I found that vibration and the bar flex gave poor results. I have use the Topeak extension with good results or now I have moved to a stem mount wireless on my TT bike.

[mlennox]

I would suggest not attaching your iBike to the Aero Bar - I tried that once and I found that vibration and the bar flex gave poor results. I have use the Topeak extension with good results or now I have moved to a stem mount wireless on my TT bike.

Are you able to get clean air for the wind sensor with the iBike sitting on the stem for your TT bike? I would rather use this position than the Topeak mount hanging down off the aerobars, but I don't see how my hands on the bars wouldn't interfere with the wind measurement.

[MikeLoos]

I would suggest not attaching your iBike to the Aero Bar - I tried that once and I found that vibration and the bar flex gave poor results. I have use the Topeak extension with good results or now I have moved to a stem mount wireless on my TT bike.

David, I would love to see a picture of how you've done the stem mount. I currently use the Topeak on my Tri bike, with success, but am always looking for other ideas and alternatives. Can you post a picture of your mount? Thanks in advance.

[mlennox]

David, I would love to see a picture of how you've done the stem mount. I currently use the Topeak on my Tri bike, with success, but am always looking for other ideas and alternatives.

Me too, please post pictures David. Thanks.

[davidpuglia]

Two sets of photos to follow - I use straight bars and I ride with my hands to the side. Aero bars are not too close together and the stem mount gives the iBike some height.

David

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[davidpuglia]

You'll need to test your particular setup for wind issues - more photos enclosed.

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[davidpuglia]

top-view.jpg (6.96 KiB) Viewed 13077 times

[mlennox]

Dave, would you mind measuring the height from the top of the stem mount to the top of the aerobars, I'm just curious what the clearance is. Also do you find that you get more error in cross-winds with the iBike in this position? What about when using the bar-end shifters? It seems to me from the photos that if the air was not entering from directly straight ahead, you would get disturbance.

Thanks in advance.

[davidpuglia]

The clearance is about 1 cm - i.e. the top of the wireless mount is about 1 cm above the aero bars. The real issue is to ensure that when you twist off the iBike it clears the arm pad base. I'm not sure about the cross winds or bar end shifters. I've done some testing against a powertap but nothing extensive - results were close maybe + / - 5%. I had a Topek extender below the aero bars at one time but I couldn't see the iBike display very well. I have since moved to the stem mount. If there is some air turbulence I'm not that concerned. For this application I'd rather be able to see the iBike and I'll sacrifice some accuracy over having little or no visual feedback from the iBike.

David

[davidpuglia]

PS - my coast downs with the stem mount vs. the Topek below the aero bars indicate no difference but they were both performed on a calm day.

[mlennox]

The clearance is about 1 cm - i.e. the top of the wireless mount is about 1 cm above the aero bars. The real issue is to ensure that when you twist off the iBike it clears the arm pad base. I'm not sure about the cross winds or bar end shifters. I've done some testing against a powertap but nothing extensive - results were close maybe + / - 5%. I had a Topek extender below the aero bars at one time but I couldn't see the iBike display very well. I have since moved to the stem mount. If there is some air turbulence I'm not that concerned. For this application I'd rather be able to see the iBike and I'll sacrifice some accuracy over having little or no visual feedback from the iBike.

David

Thanks for this Dave. I managed to install it last night in this configuration. I've got the integrated stem/wing from Profile but it's a similar configuration to yours. It barely clears the armrest pads but works fine. I'll do some coast downs and see how it goes, but I'll be willing to accept a bit more error if it means not having to use the BarXtender. I had the Xtender hanging off the aerobars in front of the wing such that the iBike was sitting centred between the bars about 3 inches down (directly above the front brakes), which forced me to move my Garmin very far forward. It worked, but on less than perfect roads it vibrated a lot, plus the flex from the aerobars didn't help matters. I much prefer the iBike on the stem and the Garmin pulled back directly in front (and below) the iBike ahead of the wing. I'll drop a picture once I've got it tested.

[MikeLoos]

Certainly can't argue with success, but at first glance I would've guessed that you'd have trouble with airflow with that mount. Before I started using the Topeak, I had a different mount (FSA) that was between and below my aerobars, with about the same clearance as yours seems to have, and was never able to get the unit calibrated. Once I dropped the unit down about 3 in. and got it out of the turbulence that seemed to have been generated from my hands, it worked a *lot* better. From conversations I've had with Richard, he helped me to understand how even little air turbulence (just from hand movement) around the unit can have much larger effects than one would guess. Again, if it's working well for you, that's great. But that's what I first thought of when I saw your mount.

[davidpuglia]

Interesting that you got the FSA mount to work. That was my first try but there was too much vibration to get any accuracy. I then moved to the Topek.

[MikeLoos]

Interesting that you got the FSA mount to work. That was my first try but there was too much vibration to get any accuracy. I then moved to the Topek.

Well, technically, I never did get the FSA to work. Had to move to the Topeak to deal with the position issues, as well as likely vibration problems.

[Site_Admin]

I think you'll want to do another Profile, instead of just loading the old profile in there. I know it gets tedious, but I think I've got unique profiles for every one of the units I either own or use, and the sensors are just, well, so sensitive, that this is probably your best bet for accuracy. Try that, save the file, and then send it in an e-mail.