Calibration with a DFPM

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benlane
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Calibration with a DFPM

Post by benlane » Fri Nov 20, 2009 6:59 am

One of the ongoing issues I have had is getting meaning ful profiles set up. I have had an ibike for 3 years and currently on GenIII.

I have followed the set up and calibration process to the letter, doing more coast downs and calibration rides than you can shake a stick at. I always need the tweaking skills of Boyd though to sort things out.

If I were to get the use of a power tap wheel, my understanding is that I can run both the ibike and powertap, can I calibrate the Ibike for all my bike set up's? Granted the rear wheel will change when I don't use the borrowed powertap.

I have collected a large amount of data using my No. 1 race bike over the last 9 months on Gen III, but want to move back onto my winter training bike and am concerned that re-creating a new profile on a different bike will cause me problems e.g. if the profile creation is not spot on, then what I am currently seeing as 200W may be 175W on the training bike.

So - in the interests of absolute parity between bikes would obtaining a power tap to calibrate help me?

Ben

travispape
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Re: Calibration with a DFPM

Post by travispape » Fri Nov 20, 2009 12:02 pm

benlane wrote:So - in the interests of absolute parity between bikes would obtaining a power tap to calibrate help me?
Probably so. One of the big benefits of calibrating with a DFPM is that you end up integrating much more data into the measurement of CdA and Crr. Coast-downs only last a few seconds, which is why it is good to do several. Also, the DFPM calibration method is more tolerant of the wind conditions--the less wind the better when doing coast-downs.

Travis

travispape
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Re: Calibration with a DFPM

Post by travispape » Sun Nov 22, 2009 6:06 pm

tommyturbo wrote:Travis,

I have friends with Powertaps, but have never really thought about borrowing one for calibration. Can this method be used with an iPro, or only an iAero?
It does require the iAero.

wellmt
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Re: Calibration with a DFPM

Post by wellmt » Thu Nov 26, 2009 4:20 pm

For what it's worth, I've had much better results just doing a regular iBike calibration procedure without a Powertap, but using double the distance (e.g 4 mile instead of 2 mile cal ride and then 12 x coastdowns). Then I use the Powertap to check the results.

On my summer bike I never had to tweak the profile at all. Every ride is within 2 watts average of the Powertap (usually sub 1 watt difference)
On my winter bike, I did several rides with the Powertap and iBike over varying terrain and simply tweaked the profile slightly to match.

I could never get the PT method to work (V4.00 firmware). It came out with the worst results I had seen.

So in my experience, a PT is a useful tool for checking results/tweaking but not for calibrating.

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lorduintah
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Re: Calibration with a DFPM

Post by lorduintah » Thu Nov 26, 2009 6:59 pm

The most solid calibration ride I have personally seen was an 8 mile (4/4) ride - the analysis came back as a straight line plot - usually I see plenty of bumps (deviations) from that corrected slope line. I was in a lucky place where there is no interference from traffic on a fairly calm day. The 2 mile calibrations tend to have too much noise in them for whatever reason.

I also tend to do at least 9 CDs.

Tom

sweet spot
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Re: Calibration with a DFPM

Post by sweet spot » Tue Dec 01, 2009 7:54 pm

About this eight-mile cal ride, would I simply keep riding at the end of the first mile, ignore the power meter as it flashes the 'bac' message, and continue to ride for three miles before turning around?

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lorduintah
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Re: Calibration with a DFPM

Post by lorduintah » Tue Dec 01, 2009 10:07 pm

Yes, whatever length you choose to ride - you can ignore the flashing, unless you slow down below 8 mph. That is the internal check for the iBike to sense a turnaround.

It does not have to be 8, but 2 is really on the short side. I just happen to have a 4 mile stretch that I can go without any stops or traffic.

Tom

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