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Minor Polar Power Issue

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Minor Polar Power Issue

Old 02-23-06, 09:13 PM
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mloywhite
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Minor Polar Power Issue

I got a great deal on a Polar Power meter, and already had an S725, so I thought I'd give it a shot. I got it setup without any trouble at all, and have tested it twice on a trainer, with very very consistent results. One problem, is an inconsistent reading on the same two rear sprockets, regardless of whether on the large or small front ring. I have a Campy Centaur 34/50 compact, with a 12-25 cassette. On the 4th largest sprocket on the rear (i.e. three shifts from the biggest, going down), I get a reading of about 50 watts higher than any of the others, when keeping speed consistent. When I shift to the next harder/smaller sprocket, it drops almost back to the same reading as before, and on the next and all other sprockets, big or little front ring, it stays consistent.

I have the main sensor as parallel and clost to the chain as possible when on the 34/12 combination, which seems to be the idea from everything I have read. Any suggestions would be appreciated.
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Old 02-23-06, 09:21 PM
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DrWJODonnell
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I have found the PPM when properly calibrated to be an accurate (if somewhat ugly) way to calculate power (particularly for average power). However, even with a shimano setup, the power output, though it does not actually change, can have false readings from one gear to the next. I do not know of any way to correct this.
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Old 02-24-06, 06:59 PM
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I tried it outdoors for a set of long slow hill repeats, about two minutes to the top, at 12 mph, in all gears, and it did not have the anomalous readings on the two gears. Thanks for the input.
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