Polar Power Question

[mloywhite]

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.

 

[Woofer]

Try repeating the test on the road outside. You will otherwise be attempting to troubleshoot the oft reported issue of problems with the Polar on a trainer. Many people have spent a lot of time on this to no resolution and some people say it works fine for them. This issue supposedly is much less but still present to a different degree outside according to people who have put another powermeter on the bike to validate their Polar setups.

 

[gvanwagner]

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.

I have found a similar problem. Only when I am in the big ring and the biggest two cogs then the readings go very high but seem to moderate to about 30 watts above actual. But it is only those two gears.

One things that you might look into doing is make your polar unit in line with the center of the cassette and a space between the front rings. That way it limits the amont of combinations that yield a big chain angle. If the unit if adjusted for a 34x12 combo then the chain angle in the largest cogs is going to be very high which cuts down on accuracy.



Greg

 

[mloywhite]

Thanks for everybody's input. I tried it outside, with a series of long slow hill repeats, at 12 mph, throughout the gears, and got no bad readings, all pretty consistent. I think I have the indoor/trainer issues like so many other people. I don't ride indoors too much, so I am not really worried about it. Thanks again for the help, Mike.

 

[Neuron]

The variation in power on the trainer is often reported with the Polar. The power I see from the big chain ring is up to 50 watts lower than similar speed and cadence in the lower chain ring. The Polar calculates power based on chain tension. The tension is determined by chain vibration (the greater the tension, the higher the chain frequency). If your variability is only with a few cogs, could you be getting an unusual vibration form those cogs?