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· jaded bitter joy crusher
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19,754 Posts
Discussion Starter · #1 ·
I've been training with a polar CS 600 w/power. Not that I need the power sensor (Who do I think I am? Magnus?) but the price was right, so I got it. It seems to work pretty consistently, but it also seems to seriously overstate my power output. According to this meter, I can be riding along steadily at around 75% of max HR (85% of LT) putting out 325-350 Watts. Now I know that ain't so. Multi-hour rides come out reporting average powers around 250 Watts, which also seems seriously high.

I carefully measured the weight and length of my chain and the distance from axle to BB, so I know those numbers are accurate.

So my question is, since I don't own a powertap or SRM, does anyone have suggestions for calibrating the power unit, or should I just shut up and return to my little Polar fantasy world, where I can produce 4.0 watts per kg without breaking a sweat.
 

· jaded bitter joy crusher
Joined
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19,754 Posts
Discussion Starter · #3 ·
ms6073 said:
1. Check that wheel size is accurate for your wheel/tire combination (ie 700cx20 or 700c x 23 etc).
2. When the power sensor was installed, was the chain weighed and that value input or was the stock weight used?
3. Did actaully measure the length of the installed chain or calculate it based on the value provided by Polar.
4. Triple check the drive side chain stay span length input into the unit - if any of these values are off 5-10%, they can effect power output accuracy.
I checked the wheel size by carefully measuring rollout with a steel tape on a smooth concrete surface. I was definitely better than 1 percent on this.

I carefully measured and weighed my chain using a good steel tape and a good kitchen scale (1 gram precision).

I measured the chain-stay span with better than 1 percent accuracy using a steel tape.
 
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