Chasing good data

Chasing good data

Postby turbomentor on Sun Jan 11, 2009 11:26 am

I've been riding with iAero GIII for the last month. Pretty satisfied so far albeit with some reservations about the devices quirks which I am learning about. I'm in a bit of a learning curve now and could use any assistance anyone can offer here.

I find myself "chasing" good real time data while riding. Before I continue, although no expert, I have assiduously read what you smart folks have put here on the forums, not to mention the owners manual. I have delved into the IB3 software and am learning how to use it. I'm a careful user of my device and pretty well think I know how to set it up and use it daily. So there is that. Not saying I'm an expert of course, but maybe better than a novice!

Anyway, I just recently received a DFPM (PT to be exact) and have been wanting to incorporate it into my rides particularly for cDA info. Well the PT is not (yet) ANT+ sport so that's out for now. What I have been trying to do is to dial in the two PMs so that OUT THE DOOR they both read pretty consistently and pretty closely. This will give me confidence in any cDA #s I come up with later on and allow me to make changes to my setup. Primarily I ride triathlons but am using my road bike at the moment for most of my training.

So Thursday I had a not so good ride in comparing the two PMs. PT was reading significantly different than the iAero for the whole ride. Frustrating. After making a post, I looked at my wind scaling factor as the ambient wind was not reading "0". So did the calculation provided to me and changed the wind scaling # in the iBike profile. So on my ride yesterday, the ambient wind was in fact 0. Hooray! Yet the two PMs still differed significantly! I made a tweak to the cRR and that made the two graphs align well and also caused the Pavg to be within about 6w of each other...totally acceptable in my mind. Yet I didn't like that I had to do all that tweaking POST RIDE...I am looking for good data while riding. I do a lot of interval riding and it does me no good to have the iAero either over or under report my wattage while riding intervals...I need to be within a fairly narrow range on the watts and I need to see that while I'm riding.

So after making a tweak to the cRR I decided to add that updated number to my iBike profile for today's ride. Today's ride was the EXACT SAME course as yesterday's, in nearly identical weather. The only difference was that I did a different set of intervals. Yesterday was 1x12 and 2x15, today was 2x15.

So for the entire ride today, I could easily tell the iAero was WAY under reporting wattage (so I used the PT CPU on my ride to ride my intervals). Came back an downloaded both files. Lo and behold, the ambient wind was -1.3 for today's ride! And the average wattage was wayyy lower then the PT file indicated, not to mention my intervals were way lower than what the PT file indicates. According to the PT file, my first int was ~237w and my second was ~225w (goal was 225-237w). According to IB, first int was 195w and second int was 190w...a major major difference.

Before you give advice, here are some backgrounds to eliminate easy stuff:
1. 7 coastdowns and a flat 4 mile cal ride. Original cRR was computed as .062 which seems a bit high. Orig wind scaling factor was something like 2.85 I think. I changed it to the current value of 2.565 after reviewing a few ride files where the ambient wind was not 0.
2. A wind offset is performed prior to every ride.
3. I do NOT do a tilt cal prior to every ride.
4. Indoor temp was within 7 deg of outdoor temp prior to riding. In any case, I am happy to ignore first 10 mins worth of data as it is my warmup.

So here is the crux: I really think that the IB is a pretty cool device and has a lot going for it. Not being a GI or GII user, I can't comment on the upgrade to GIII but the tilt functions and the stability of the mount and the device in general seem pretty good to me. My major complaint at this point is REPEATABILITY. I guess in the end it does not really matter if the iAero mirrors the PT because if all I ever had was the iAero it would be all I know. However, I am seeing in comparison to the PT that it is not putting out the same data day to day...and that is not good. If my ambient wind was 0 yesterday, for today's ride on the same course it should also be zero! So somewhere along the line something isn't quite "right".

I'm hoping that some smart folks can give me some ideas so I can stop chasing good data, or using the IB software to obtain good data...I need to be certain that the IB is reliable enough to give me solid data in real time and that the data I'm seeing day to day is accurate enough for me to use in the training environment I ride in.

I am attaching the Powertap CSV file and today's ride file if anyone wants to monkey around with them. Again, I can go into IB and get the two ride files to marry up; what I'm looking for is a solution that will allow me to do this OUT THE DOOR each and every day and not have to rely on the IB software to do it post ride.

Thanks!
Attachments
iBike_01_11_2009_0738_22_Miles.csv
iBike ride file (unedited)
(933.52 KiB) Downloaded 106 times
1_11 powertap.csv
Powertap ride file
(139.07 KiB) Downloaded 97 times
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Re: Chasing good data

Postby coachboyd on Sun Jan 11, 2009 11:37 am

The easy solution is going to be to do another calibration ride. Make sure your power tap records the data as well. Reset it when you start your cal ride, and stop it from recording when you finish so you only have the 4 miles on the power tap.

When you get home you can go to the profiles, and import the power tap csv file (obviously you are going to want to download the power tap into device agent and save the csv file). This will match your aero and friction numbers to the power tap power, and given the wind scaling and riding tilt you will have a profile.

I can take a look at the files, but it will have to be this afternoon. I am about to head out for a ride myself.
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Re: Chasing good data

Postby Velocomp on Sun Jan 11, 2009 11:51 am

Where is your iBike mounted on your bicycle? Stem or handlebar? If on the handlebars, where?
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Re: Chasing good data

Postby Velocomp on Sun Jan 11, 2009 11:53 am

Something definitely weird is going on with your setup.

I too did a ride this AM, with a CinQo as my DFPM. I am getting great results, with high consistency.
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iBike_01_11_2009_0928_8_Miles__solo.csv
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Re: Chasing good data

Postby turbomentor on Sun Jan 11, 2009 2:34 pm

coachboyd wrote:The easy solution is going to be to do another calibration ride. Make sure your power tap records the data as well. Reset it when you start your cal ride, and stop it from recording when you finish so you only have the 4 miles on the power tap.

When you get home you can go to the profiles, and import the power tap csv file (obviously you are going to want to download the power tap into device agent and save the csv file). This will match your aero and friction numbers to the power tap power, and given the wind scaling and riding tilt you will have a profile.

Thanks for the info Coach Boyd. I'll do another cal ride tomorrow. Import the PT CSV file into the cal ride? I know how to import the PT CSV file into a ride file but not the cal ride file. Can you expand on what you are saying...I will do this cal ride tomorrow.

coachboyd wrote:I can take a look at the files, but it will have to be this afternoon. I am about to head out for a ride myself.


I would appreciate it if you could give me any kind of feedback onn my files. It would be very helpful. I can see that with the right setup, the IB can be as good as a PT...what am I doing so wrong on my setup? :) Frustrating.

Note that this will be my second cal ride for this iAero. This cal ride included 7 coastdowns and a 4 mile out and back on a flat road with a very light wind that was all crosswind (wind was from the E, ride was N then S). I tried to be very careful about the cal ride!

It sounds like you are saying "use the PT data as 'absolute' to come up with solid #s for cDA and cRR". While I agree this will probably work, I am thinking that the iAero is designed to be set up without the use of a DFPM? I think the idea is that it can replace a DFPM and you shouldn't need a DFPM to set it up properly.
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Re: Chasing good data

Postby turbomentor on Sun Jan 11, 2009 2:48 pm

Velocomp wrote:Where is your iBike mounted on your bicycle? Stem or handlebar? If on the handlebars, where?


Handlebars. I primarily ride in the drops but on my rest intervals I am riding on the hoods. I did my coast downs and my cal ride 100% in the drops.

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Re: Chasing good data

Postby turbomentor on Sun Jan 11, 2009 2:56 pm

Velocomp wrote:Something definitely weird is going on with your setup.


OK. Any suggestions on fixing the problem? :) I'm open to coming to the shop to show you my coast downs/cal ride technique to see if I am really doing something "off".

Velocomp wrote:I too did a ride this AM, with a CinQo as my DFPM. I am getting great results, with high consistency.


It looks as though your results are pretty good, with an R^2 value of .667. Was that "untweaked" data or did you have to mess with wind scaling, cRR etc?
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Re: Chasing good data

Postby coachboyd on Sun Jan 11, 2009 4:49 pm

OK,

When I took your profile and switched the numbers back to the original numbers you had before you changed them, the data looks a LOT better. As explained in another thread, the average ground wind speed does not and SHOULD not always equal 0 on a looped ride. There are too many variables for average ground wind to be zero.

If you change the numbers on your profile back to what you had when you did coastdowns and the 4 mile ride, you should get much better results. If you would like to do another calibration ride using the power tap data, here is what you can do.

Get to the point where you are going to do your calibration ride. Check your tilt and wind just to be sure they are good.
Clear out the data on the power tap (do a trip reset). Go into the setup screen on the iBike and do a cal ride
When you finish your cal ride on the iBike, take the power tap off the mount so it no longer records power

When you get home, download your power tap first (you should only have the 4 mile file on there). Save the csv file somewhere that you can easily find it.
In the iBike software, hit profiles and download coastdowns and cal ride. It will start downloading the cal ride
Then hit the tab that says "iBike +DFPM". You can look for your power tap csv file and it will read and sync the speed data to get good power comparison.
This will give you aero and friction values based on the power tap watts. Given the wind scaling and riding tilt from the cal ride, you will have the cda and crr and a full profile that you can send to your iBike.
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Re: Chasing good data

Postby turbomentor on Sun Jan 11, 2009 5:34 pm

I will do precisely what you recommend Coach Boyd, and thanks for the input. I very much appreciate your time.
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