Stages Power Meter

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Re: Stages Power Meter

Postby Carrots » Wed Mar 12, 2014 9:14 am

AKO wrote:So nothing that can't be done through a Garmin 510 besides maybe firmware update?


Essentially yes (can't recall specifically probably even more on Garmin than iPhone with exception to updates).


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by BNA » Wed Mar 12, 2014 9:23 am

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Re: Stages Power Meter

Postby Xplora » Wed Mar 12, 2014 9:23 am

I thought Stages was sending messages 60 times a second, isn't it? Vs 1 a second via ANT+??
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Re: Stages Power Meter

Postby doggatas » Wed Mar 12, 2014 9:49 am

Rode with the Stages on last night. It seemed ok, the information displayed on the Garmin screen (3 sec AVG) seemed a little delayed compared to the SRM. At some stage I will put the Stages arm on the SRM crank and borrow another Garmin for 2 data streams, this will allow me to compare the data between the two devices.
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Re: Stages Power Meter

Postby george-bob » Wed Mar 12, 2014 9:52 am

doggatas wrote:Rode with the Stages on last night. It seemed ok, the information displayed on the Garmin screen (3 sec AVG) seemed a little delayed compared to the SRM. At some stage I will put the Stages arm on the SRM crank and borrow another Garmin for 2 data streams, this will allow me to compare the data between the two devices.


Yep, there is a bit of lag, about 1sec, DCrainmaker goes into a lot of detail about it. I suspect it has to do with the accelerometer-based velocity calculations, these are much more intensive than the magnets used on SRM.
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Re: Stages Power Meter

Postby doggatas » Wed Mar 12, 2014 10:08 am

Thanks for clearing that up george, much appreciated.
If I have the Stages on the SRM I should be able to approximately workout my left/right % at various power levels from the data right? Doesn't really worry me but if I can know, why wouldn't I want to know.

(yes, if I have my time again and the Stages was available I would simply have two Stages)


StgP = Stages power
SrmP = SRM Power
LLP = Left Leg Power
*Approx Right Leg Power = ARLP


LLP = StgP/2
ARLP = SrmP - LLP

*Avg right leg power at various power levels
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Re: Stages Power Meter

Postby george-bob » Wed Mar 12, 2014 12:02 pm

I doubt it TBH, the difference in power reported between power meters varies by a few watts, I suspect this difference would be enough to make the readings fairly noisy. Combine that with any left/right leg discrepancies vary through the power range (so at high power differences may be more pronounced for instance) and simply looking at average power off two different meters would probably not be much use.


This is from the DCrainmaker review:


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Re: Stages Power Meter

Postby Alex Simmons/RST » Wed Mar 12, 2014 12:11 pm

doggatas wrote:Thanks for clearing that up george, much appreciated.
If I have the Stages on the SRM I should be able to approximately workout my left/right % at various power levels from the data right? Doesn't really worry me but if I can know, why wouldn't I want to know.

(yes, if I have my time again and the Stages was available I would simply have two Stages)


StgP = Stages power
SrmP = SRM Power
LLP = Left Leg Power
*Approx Right Leg Power = ARLP


LLP = StgP/2
ARLP = SrmP - LLP

*Avg right leg power at various power levels


Only if the both meters are also accurate, or have the exact same level of inaccuracy.

e.g. let's assume (say) you are exactly 50:50 in your pedalling but the Stages read 3% higher than the SRM (say).
Hence
SrmP= StgP * 0.97

Then using your calculations:

LLP = StgP/2 = StgP x 0.50

ARLP = SrmP - LLP
= (StgP * 0.97) - (StgP * 0.50)
= StgP * (0.97 - 0.50)
= StgP * 0.47


So even though you are actually 50:50 in this example, these calculations would suggest you are 0.50/0.97 : 0.47/0.97 = 51.5% : 48.5%.

See the problem?

IOW to use a Stages along with another meter to calculate left:right power ratio, you also need to know that both meters are accurate, or have the same level of inaccuracy.
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Re: Stages Power Meter

Postby doggatas » Wed Mar 12, 2014 12:59 pm

Alex Simmons/RST wrote:IOW to use a Stages along with another meter to calculate left:right power ratio, you also need to know that both meters are accurate, or have the same level of inaccuracy.


Yep totally agree.

Accepting that the power meters are not recording at the same level of (in)accuracy, working out the constant discrepancies between the two power meters when your left/right leg power might not be 50/50 across any or all levels of exertion makes working out the discrepancy pointless as well.
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Re: Stages Power Meter

Postby Carrots » Wed Mar 12, 2014 2:10 pm

So in other news... I bought a jeep. So I'm going to need a bigger bike.

:/


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Re: Stages Power Meter

Postby doggatas » Wed Mar 12, 2014 2:46 pm

Carrots wrote:So in other news... I bought a jeep. So I'm going to need a bigger bike.

:/


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Or more bikes.....
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Re: Stages Power Meter

Postby jasonc » Wed Mar 12, 2014 2:56 pm

as long as you didn't buy a patriot or whatever the little 4 cylinder is, we're ok.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Wed Mar 12, 2014 5:36 pm

Just for fun, during my warm up for a 20-min performance test the other day, I was L52:48R at times, which is kind of amusing.

During the test I was L49:51R on average. The nature of my pedalling each side is quite different, which is to be expected*.

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That's from a Computrainer spinscan, which I'd take with a large grain of salt, and shows the proportion of total torque applied during each 15 degrees of the crank revolution for each side.

The L-R % numbers are obvious. The numbers at the top are ratio of peak to average torque, and the degrees are "average angle of attack", meaning where on average you put most force through the crank on each side, i.e. on the right it's a 92 degrees past top dead centre, and on the left it's 107 degrees past top dead centre.

But like I said, take spinscan with large grain of salt. It's a downstream measurement, meaning left and right means measurement of total force from both legs wheil either left or right crank is forward of the BB, and not each leg/crank independently.


* Keep in mind I have a left lower leg amputation and ride with a prosthetic, and on that side the pedal cleat is effectively positioned under where my ankle would have been, hence why the power is applied later, on average.
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Re: Stages Power Meter

Postby Carrots » Wed Mar 12, 2014 8:33 pm

Alex Simmons/RST wrote:* Keep in mind I have a left lower leg amputation and ride with a prosthetic, and on that side the pedal cleat is effectively positioned under where my ankle would have been, hence why the power is applied later, on average.


Interesting. One of our group is pretty much identical amputation wise. Be interesting to see his figures to see if they mirror yours based on similar style. Might have to convince him to get a PM.
The mad bugga even won a gold medal at the 84 Paralympics as a runner!


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Re: Stages Power Meter

Postby AKO » Mon Mar 17, 2014 1:21 pm

Got off night shift yesterday morning and had a sleep before throwing the stages on and found the front derailleur was seized solid. So I decided on a nice flat 18 klm out and back and put it in the large chain ring. It was interesting to see the numbers and how they fluctuate. Looking forward to doing some testing and building a training plan around it.
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Re: Stages Power Meter

Postby GAV!N » Tue Mar 25, 2014 11:02 am

Ordered mine today. 30th birthday present to myself :D
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Re: Stages Power Meter

Postby Ross » Tue Mar 25, 2014 11:30 am

Sort of related question, say you have a PM and when out training you notice a significant (>10%) imbalance of power between right and left. Can you train yourself out of this by conciously pedalling harder with the deficiant leg? Presuming both legs are injury free and the same length.
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Re: Stages Power Meter

Postby Carrots » Tue Mar 25, 2014 3:24 pm

Has anyone had/notice this happen yet on their Stages...?

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Re: Stages Power Meter

Postby Xplora » Wed Mar 26, 2014 8:16 am

Ross wrote:Sort of related question, say you have a PM and when out training you notice a significant (>10%) imbalance of power between right and left. Can you train yourself out of this by conciously pedalling harder with the deficiant leg? Presuming both legs are injury free and the same length.

You could do single leg work to balance it out, but SHOULD you? You might have an underlying pelvic tilt or any number of other weird things that your body compensates for. Might be cause to visit a fitter, but something I have concluded is that your body is very good at protecting itself from injury. You could actually be avoiding injury by favouring the right side when fatigued.

Bear in mind you spend more time off the bike than on it. I have found that the work Mr Hogg did with me seriously changed my previous balance. I notice the impact of the wedging and shimming if I take time off the bike. I have no doubt that chasing L R symmetry via muscle development would be equally confronting.
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Re: Stages Power Meter

Postby Arlberg » Thu Mar 27, 2014 6:31 am

Anyone else think the Stages may be a bit overgenerous with its power output readings when compared with other powermeters? Sometimes I wonder if I really am holding a 360W average for 9-10 minutes or so on an ascent such as Bobbin East or Pie in the Sky. When comparing my segment times/power outputs on Strava with other riders who are using powermeters, the Stages seems to read a bit higher, although of course I have no idea how accurate the powermeters of the riders I am comparing my outputs with are.
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Re: Stages Power Meter

Postby GAV!N » Thu Mar 27, 2014 7:54 am

Based on the BikeRadar review, I'd suggest yes, maybe Stages are slightly generous, but I don't think it would be a huge difference. There's also the possibility your left leg is strong, giving a high reading.

Comparing to other riders is also going to be variant on their weight and other conditions. were they in a group? Did they have a tail wind?

Obviously stages aren't going to be as accurate as SRM etc because of the left leg only being measured, but as long as it's consistent for you it should be a good training tool...
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Re: Stages Power Meter

Postby dale79 » Thu Mar 27, 2014 8:21 am

Arlberg wrote:Anyone else think the Stages may be a bit overgenerous with its power output readings when compared with other powermeters? Sometimes I wonder if I really am holding a 360W average for 9-10 minutes or so on an ascent such as Bobbin East or Pie in the Sky. When comparing my segment times/power outputs on Strava with other riders who are using powermeters, the Stages seems to read a bit higher, although of course I have no idea how accurate the powermeters of the riders I am comparing my outputs with are.


my stages is with in 1w of my wahoo kickr. that's close enough for the training I do.
my wahoo also reads with in 4w of a mates quark..

these are the exact same efforts on the wahoo when I first got it so I had the stages reporting to the garmin and wahoo reporting to trainer road

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Re: Stages Power Meter

Postby Ross » Thu Mar 27, 2014 8:40 am

Arlberg wrote:Anyone else think the Stages may be a bit overgenerous with its power output readings when compared with other powermeters? Sometimes I wonder if I really am holding a 360W average for 9-10 minutes or so on an ascent such as Bobbin East or Pie in the Sky. When comparing my segment times/power outputs on Strava with other riders who are using powermeters, the Stages seems to read a bit higher, although of course I have no idea how accurate the powermeters of the riders I am comparing my outputs with are.


Without knowing who the other riders are and their weights and as you say the accuracy of their PMs then it probably isn't a fair comparison. My understanding is a light person generally won't be putting out the same power as a heavier person even if they do the same time up a climb.

You just need the PM to give consistent readings so you can compare your workout to last week's, yesterday's and today's, rather than compare to Jimmy and John who are 20kg heavier and have Quarq and a Powertap.
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Re: Stages Power Meter

Postby boss » Thu Mar 27, 2014 11:03 am

Ross wrote:
Arlberg wrote:Anyone else think the Stages may be a bit overgenerous with its power output readings when compared with other powermeters? Sometimes I wonder if I really am holding a 360W average for 9-10 minutes or so on an ascent such as Bobbin East or Pie in the Sky. When comparing my segment times/power outputs on Strava with other riders who are using powermeters, the Stages seems to read a bit higher, although of course I have no idea how accurate the powermeters of the riders I am comparing my outputs with are.


Without knowing who the other riders are and their weights and as you say the accuracy of their PMs then it probably isn't a fair comparison. My understanding is a light person generally won't be putting out the same power as a heavier person even if they do the same time up a climb.

You just need the PM to give consistent readings so you can compare your workout to last week's, yesterday's and today's, rather than compare to Jimmy and John who are 20kg heavier and have Quarq and a Powertap.


Yeah you need to compare watts per kilogram rather than simply watts.

When comparing my watts per kilo to a friend who runs Vectors, the result is very similar.

E.g. I might put out 300w for 10 minutes up a climb, and a friend puts out 342w for the same duration. I am 70kg, he is 80kg. We both have the same w/kg (4.29 w/kg) so we finish with similar times.

This watts per kilo stuff also explains why lighter riders have a big advantage climbing. 6w/kg for 60kg whippet is 360w. 6w/kg for a 90kg gentleman is 540w.

Obviously when you are larger in stature you have a corresponding increase in muscle mass and your heart and lungs are bigger too - but the increase in power for kg isnt 1:1. i.e. 360w at 60kg is easier to hold than 540w at 90kg.
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Re: Stages Power Meter

Postby toolonglegs » Thu Mar 27, 2014 4:09 pm

Arlberg... 360w at 80kgs ( I think that's what you said roughly in another thread ) ... Nice :-) .
As long as you think your stages is giving you consistent results it doesn't really matter. If you are pushing higher and higher numbers over a short period then maybe it is starting to drift.
Is there a way to check the calibration personally on a stages?.
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Re: Stages Power Meter

Postby Tarquin » Thu Mar 27, 2014 8:02 pm

A tailwind/headwind will still affect the time and power. You can only really compare efforts done at the same time in a race or back to back repeats.

Up a 3km climb near me my best time doesn't have my highest power.

Did three back to back repeats last night, not my highest power (350w) but I need to build on my recovery between efforts.

327w, 336w and 321w respectively for each one, it's a 3.1km 7% climb so gives you a good workout!
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