Power meters and crank arms
12-29-23, 11:11 AM
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AFAIK, all crank based PM's are installed on the crankarm by the maker of the PM. And AFAIK, the PM itself is just a strain gauge.
Perhaps the length does affect how much strain they detect at the particular location they are installed. However being installed by the maker, they are going to calibrate it to what ever is correct.
If you happen to have one that you install yourself, then what does the maker of the PM say about it? Or are you modifying a crank with some adapter or DIY? If so, I'd say expect your power to be incorrect.
Perhaps the length does affect how much strain they detect at the particular location they are installed. However being installed by the maker, they are going to calibrate it to what ever is correct.
If you happen to have one that you install yourself, then what does the maker of the PM say about it? Or are you modifying a crank with some adapter or DIY? If so, I'd say expect your power to be incorrect.
12-29-23, 11:56 AM
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12-29-23, 12:11 PM
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I have a Domane+ with a TQ e-assist drive. It has an integral power meter which provides readings that I find suspect. I have never used a power meter before so don't really have anything to compare it with and have not been able to find any information on their power meter. I did put 172.5mm cranks on it from the stock 175. I believe this would be a hub power meter. Thanks
12-29-23, 12:23 PM
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I have a Domane+ with a TQ e-assist drive. It has an integral power meter which provides readings that I find suspect. I have never used a power meter before so don't really have anything to compare it with and have not been able to find any information on their power meter. I did put 172.5mm cranks on it from the stock 175. I believe this would be a hub power meter. Thanks
Last edited by PeteHski; 12-29-23 at 03:23 PM.
12-29-23, 03:05 PM
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Hub Power Meter, wont care what is driving it... Human, electric, 100mm cranks. It measures power at the hub after the drivetrain has done it's stuff.
Crank Power meter, do care about crank length (but usually non-adjustable). (The new Shimano PM & Di2 even takes which chainring into account.)
Pedal Power Meters, Example Garmin Rally, You configure the pedals for the crank length in use.
My coach had concerns regarding my Stages Crank PM not matching my Wahoo Kickr Bike (hub) PM.
I borrowed a pair of Garmin Vector 3 pedals and did a comparison.
All 3 PMs were within 2-3%, plenty close enough.
Modern PMs are both precise and accurate.
Barry
Crank Power meter, do care about crank length (but usually non-adjustable). (The new Shimano PM & Di2 even takes which chainring into account.)
Pedal Power Meters, Example Garmin Rally, You configure the pedals for the crank length in use.
My coach had concerns regarding my Stages Crank PM not matching my Wahoo Kickr Bike (hub) PM.
I borrowed a pair of Garmin Vector 3 pedals and did a comparison.
All 3 PMs were within 2-3%, plenty close enough.
Modern PMs are both precise and accurate.
Barry
Last edited by Barry2; 12-29-23 at 03:16 PM.
