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jaded bitter joy crusher
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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.
 

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Simple concept with Polar CS 600 W.I.N.D. Power - the reliability of the data output is directly proportional to the data input during setup. Based on my experience with the CS600 w/power installed on a Giant TCR TT Composite, here are some things to check that will impact the power data output.

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.

Once you have checked these settings, I would suggest you consider ridng with someone who has also has a PM and periodically compare power data . Also, I have found that during training rides, power intervals with the CS600 can be easier to manage by using the 'Plan an Exercise' feature of the Polar Pro Trainer 5 software. Once you plan a power based exercise and upload to the CS600, when you activate the 'exercise' an additional screen is added that will display a countdown timer for each interval phase in the top row, a power graph in the middle row, and HR in the bottom row. Regardless of the recording interval you have set, the computer updates pretty quickly so the Power graph is a semi-real time average power graph that can be used to maintain specified power output within the specified limits for each interval phase. Finally, if you are not already using it, I think you will find that Cycling Peaks WKO 2.2 is a much better analysis tool than Polars software when it comes to reviewing power data after a training ride.
 

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jaded bitter joy crusher
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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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Check the lateral displacement of the chain over the sensor in the big chain ring and biggest rear cog - the little dot in the center of the top of the sensor is the sweet spot and if the chain is more than 25-30mm laterally from that dot, sensor output gets flaky. Also, when the chain is in the small chain ring and smallest rear cog and you hold the rear wheel to prevent it from turning, apply pressure to the crank so that the chain is taught and note the distance between the bottom of the chain and the top of the power sensor? If it is more than 2-3mm that can also effect accuracy in other gears.

Also, in the big/big combination If it is more than 2-3mm above the sensor needs to be
 
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