DFPM, iaero filter, and sprints

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kylef
Posts: 25
Joined: Mon Feb 16, 2009 3:22 pm

DFPM, iaero filter, and sprints

Post by kylef »

This entire season I've not had a sprint with a peak power greater than 1000 watts. That's taking into account the cumulative data from my season so far using the iaero and srm with the iaero's filter on. I'm much more diesel than sprinter, so I've been trying to improve my sprint power with some sprint workouts. The greatest benefit my sprint power numbers have seen is turning off the iaero's filter function. The downloaded numbers break a thousand watts with ease. *sigh*

I'd been using the filter since it purportedly is a fix for the wattage spikes the SRM occasionally generates. I've not found this to be the case. Where previously a spike of 2000 watts would show up I see instead the spike rolled into subsequent samples. ie- the samples for power will be 1600, 900, 400, 20. Without the filter it's more like a single corrupt sample.

Does the filter only implement a rolling average or is there some logic in there to look for outlying power spikes? The SRM power spike situation I've noticed is when cadence is zero the first non-zero power sample may be in error. I believe this is more likely to happen if the rider backpedals a bit. It seems like could be better handled in post-processing the file at download instead of filtering the entire data stream in the iaero itself.
coachboyd
Posts: 527
Joined: Thu Mar 27, 2008 7:01 pm
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Re: DFPM, iaero filter, and sprints

Post by coachboyd »

The SRM filter that we put in place was to fix the false spikes of about 2800 watts. I have heard that with newer firmware in the SRM this hasn't been an issue anymore, but they also haven't sent me a crank to play with yet.

Keep in mind that we did this to fix one of their problems and we can't devote a ton of resources to making everybody else's products work better.

The filter that we applied is the same one that is applied to seeing iBike only watts. So whereas if you compare a DFPM to an iBike you may see the DFPM is a bit jumpier than the iBike. With the filter setting on, the two should look like they have about the same responsiveness.

Hope this helps
Boyd Johnson
http://www.boydcycling.com - high performance carbon wheels and accessories
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