Shimano R9100-P Powermeter

Discuss light weight issues concerning road bikes & parts.
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mds
Posts: 199
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by mds

PinaF8 wrote:Good stuff!

I wouldn’t even bother trying to get Strava to do anything as they are not great at translating these data. I prefer to use golden cheetah as it is a free and a very robust software. However, you do have to your homework in order to understand the available data. If I were you I would use a computer that will show dual leg output.

Have fun with your new toy.


Thanks. PC8 can display a power balance field via a custom screen setup. I do see power balance data for this ride in TrainingPeaks.

Update: regarding the Strava "spike" issue, the ride's TrainingPeaks power plots do not have spikes. So IMO the issue is more likely a Stava analysis/plotting bug.
2009 Look 595


PinaF8
Posts: 188
Joined: Mon Jan 23, 2017 8:05 am

by PinaF8

mds wrote:
PinaF8 wrote:Good stuff!

I wouldn’t even bother trying to get Strava to do anything as they are not great at translating these data. I prefer to use golden cheetah as it is a free and a very robust software. However, you do have to your homework in order to understand the available data. If I were you I would use a computer that will show dual leg output.

Have fun with your new toy.


Thanks. PC8 can display a power balance field via a custom screen setup. I do see power balance data for this ride in TrainingPeaks.

Update: regarding the Strava "spike" issue, the ride's TrainingPeaks power plots do not have spikes. So IMO the issue is more likely a Stava analysis/plotting bug.


Let me get this right, does shimano power meter connect as a single power meter for both legs or do you have to connect the left and the right into the computer?
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mds
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by mds

PinaF8 wrote:Let me get this right, does shimano power meter connect as a single power meter for both legs or do you have to connect the left and the right into the computer?


R9100-P connects as a single power meter to PC8.

With TrainingPeaks app, I see a unique power balance entry (eg 53.1/46.9%) in each and every data sample recorded during the ride.

My guess: R9100-P measures left and right power independently, and effectively sends both "total power" as well as "power balance" in the ANT+ protocol.

The head unit can display either or both, or I suppose alternatively multiply the percentages and display left and right separately.
2009 Look 595

BdaGhisallo
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by BdaGhisallo

mds wrote:
PinaF8 wrote:Let me get this right, does shimano power meter connect as a single power meter for both legs or do you have to connect the left and the right into the computer?


R9100-P connects as a single power meter to PC8.

With TrainingPeaks app, I see a unique power balance entry (eg 53.1/46.9%) in each and every data sample recorded during the ride.

My guess: R9100-P measures left and right power independently, and effectively sends both "total power" as well as "power balance" in the ANT+ protocol.

The head unit can display either or both, or I suppose alternatively multiply the percentages and display left and right separately.


Interesting.

PinaF8
Posts: 188
Joined: Mon Jan 23, 2017 8:05 am

by PinaF8

mds wrote:
PinaF8 wrote:Let me get this right, does shimano power meter connect as a single power meter for both legs or do you have to connect the left and the right into the computer?


R9100-P connects as a single power meter to PC8.

With TrainingPeaks app, I see a unique power balance entry (eg 53.1/46.9%) in each and every data sample recorded during the ride.

My guess: R9100-P measures left and right power independently, and effectively sends both "total power" as well as "power balance" in the ANT+ protocol.

The head unit can display either or both, or I suppose alternatively multiply the percentages and display left and right separately.


Power meter is a dummy sensor and it will not calculate anything. Your PC8 is only picking up one sensor. At this time SRM does not believe in having dual leg readings. What you are seeing in your power balance is just an estimate and not actual values. I could be wrong but this is how I am understanding.
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mds
Posts: 199
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Location: California

by mds

PinaF8 wrote:Power meter is a dummy sensor and it will not calculate anything. Your PC8 is only picking up one sensor. At this time SRM does not believe in having dual leg readings. What you are seeing in your power balance is just an estimate and not actual values. I could be wrong but this is how I am understanding.


Maybe a misunderstanding? I have a Shimano power meter on my bike now, the SRM is in a box awaiting sale.

The Shimano has a sensor mounted on each crank arm. IMO the Shimano doesn't need to estimate anything, it has real left/right data.
2009 Look 595

PinaF8
Posts: 188
Joined: Mon Jan 23, 2017 8:05 am

by PinaF8

mds wrote:
PinaF8 wrote:Power meter is a dummy sensor and it will not calculate anything. Your PC8 is only picking up one sensor. At this time SRM does not believe in having dual leg readings. What you are seeing in your power balance is just an estimate and not actual values. I could be wrong but this is how I am understanding.


Maybe a misunderstanding? I have a Shimano power meter on my bike now, the SRM is in a box awaiting sale.

The Shimano has a sensor mounted on each crank arm. IMO the Shimano doesn't need to estimate anything, it has real left/right data.



Perhaps, but the PC8 is only picking up one from the two sensors.
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mds
Posts: 199
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by mds

PinaF8 wrote:Perhaps, but the PC8 is only picking up one from the two sensors.


Perhaps, but I suppose differently.

Shimano effectively provides PC8 with "total power" and "power balance". PC8 effectively records both. I see this data in the log.

I assume "power balance" is real, for obvious reasons.

Note: On Shimano the two sensors and control box are connected via wires through the spindle. Unlike Pioneer.
2009 Look 595

ipenguinking
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by ipenguinking

I'm getting mine next Tuesday. Anything I need to pay attention when installing? I read thru the manual and process looks very simple.

mds
Posts: 199
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by mds

ipenguinking wrote:I'm getting mine next Tuesday. Anything I need to pay attention when installing? I read thru the manual and process looks very simple.


Yes simple.

Don't forget to install the magnet first. :oops: Can't really be done accurately after the DS crank is in place.
2009 Look 595

PinaF8
Posts: 188
Joined: Mon Jan 23, 2017 8:05 am

by PinaF8

mds wrote:
PinaF8 wrote:Power meter is a dummy sensor and it will not calculate anything. Your PC8 is only picking up one sensor. At this time SRM does not believe in having dual leg readings. What you are seeing in your power balance is just an estimate and not actual values. I could be wrong but this is how I am understanding.


Maybe a misunderstanding? I have a Shimano power meter on my bike now, the SRM is in a box awaiting sale.

The Shimano has a sensor mounted on each crank arm. IMO the Shimano doesn't need to estimate anything, it has real left/right data.


Which SRM power meter do you have for sale?
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mds
Posts: 199
Joined: Sat Dec 13, 2008 6:28 pm
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by mds

PinaF8 wrote:Which SRM power meter do you have for sale?

Used SRM DA 7900 Wireless PowerMeter #19349 2012 53/39 172.5mm

Reconditioned last week Nov 3, 2017 by SRM USA, including new firmware, new battery, and calibration.

Listed on ebay.
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cunn1n9
Posts: 88
Joined: Sat Jan 15, 2011 1:24 am

by cunn1n9

PinaF8 wrote:
mds wrote:
PinaF8 wrote:Let me get this right, does shimano power meter connect as a single power meter for both legs or do you have to connect the left and the right into the computer?


R9100-P connects as a single power meter to PC8.

With TrainingPeaks app, I see a unique power balance entry (eg 53.1/46.9%) in each and every data sample recorded during the ride.

My guess: R9100-P measures left and right power independently, and effectively sends both "total power" as well as "power balance" in the ANT+ protocol.

The head unit can display either or both, or I suppose alternatively multiply the percentages and display left and right separately.


Power meter is a dummy sensor and it will not calculate anything. Your PC8 is only picking up one sensor. At this time SRM does not believe in having dual leg readings. What you are seeing in your power balance is just an estimate and not actual values. I could be wrong but this is how I am understanding.



If you have a look at the Shimano docs on this what you will find is that it works similar to other dual sided PM’s (eg Vector or Powertap p1 etc) but with one important difference. With most dual sided PMs one crank or pedal is the slave (usually the left side) and it transmits to the master (usually the right side). This is then combined and sent as a single data stream to the head unit that will have the following day items in it: total power, Power balance l/r, torque effectiveness l/r. Shimano has direct linked via a wire the two sides together so it eliminates one wireless transmission thus making it less likely to have errors (eg my old vectors use to loose the L side sometimes). On the Shimano the L and R data for the above data items are combined and sent as a single stream. If your srm head unit can display l/r balance and l/r torque effectiveness then you should get that data. I never look at it while riding.

I just upgraded to the Shimano from Stages so that I would have the complete picture of my power rather than the assumption of L=R. I am actually 48/52 according to the Shimano (overall ride average). Thing I notice from the Shimano is very stable cadence due to magnet that works down to very low cadence. The Stages was flaky below 32 rpm due to its sample rate (64 samples/sec). If you understand the maths behind this you will know why 32 is the limit for the Stages.

I also see much faster pickup of power changes on the Shimano also and I would think this is due to much more accurate cadence detection.


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CallumRD1
Posts: 83
Joined: Mon Apr 03, 2017 2:54 pm

by CallumRD1

cunn1n9 wrote:[snip]

I just upgraded to the Shimano from Stages so that I would have the complete picture of my power rather than the assumption of L=R. I am actually 48/52 according to the Shimano (overall ride average). Thing I notice from the Shimano is very stable cadence due to magnet that works down to very low cadence. The Stages was flaky below 32 rpm due to its sample rate (64 samples/sec). If you understand the maths behind this you will know why 32 is the limit for the Stages.

[snip]


I'll bite. Why is 32 rpm the lower limit for the stages? At that cadence the powermeter is sampling at 120 samples/revolution of the crank.


youngs_modulus
Posts: 512
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Location: Madison, WI USA

by youngs_modulus

I'd like to know the same thing. Why is the sample rate the problem? Are you suggesting some sort of aliasing? That should be less of a problem as cadence declines, not more of one.

I'd have expected the issue to be that the Stages accelerometer-based cadence sensor became inaccurate when faced with the small radial acceleration that comes at 32 RPM.

And finally: were you pedaling with a cadence below 32 RPM very often? If so, why?

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