Stages Power Meter
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Re: Stages Power Meter
Postby dalai47 » Wed Apr 02, 2014 11:39 am
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Re: Stages Power Meter
Postby Alex Simmons/RST » Wed Apr 02, 2014 1:07 pm
Very slightly (almost negligible) since the assumption of constant crank velocity during a pedal stroke isn't really ever the case, however it's not nearly as much of an error as what non-circular rings introduce. Certainly not enough to explain the sort of power differential many suggest they experience.boss wrote:Alex, what Xplora seemed to suggest (at least from my reading) is that power meters read high on climbs (or low on flats) regardless of q-rings or regular rings. Was this a misinterpretation?
Some years back Eric Lin did some high frequency measurements of velocity during some simulated flat and climbing. I tagged the pics for reference.
Here we can see some charts plotting the bike velocity (m/s) pseudo-sinusoidal variation while riding on the flat and on a climb (simulated). The horizontal axis is time at high sample rate - each peak and trough represents one half of a pedal stroke.
Keep in mind the shortened vertical axis is designed to highlight this variance. Plotted with axis starting at zero would see a very slightly wavy line.
We can see a maximum variance in velocity of ~0.5% on the flat:
and ~ 2% on a simulated +10% gradient:
Now that 2% variation in velocity <> 2% error in power, it will be less than that, but I'm not doing the maths right now.
Elliptical rings exacerbate this issue somewhat.
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Re: Stages Power Meter
Postby boss » Wed Apr 02, 2014 1:14 pm
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Re: Stages Power Meter
Postby Ignoto » Mon Apr 07, 2014 8:55 pm
I know the wheel magnet was used instead of the GPS on the Garmin as it provides a more accurate figure (especially if you're riding in tree coverage). So was the figure my Garmin was getting from the GPS or does Stages somehow calculate the speed you're going as well?
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Re: Stages Power Meter
Postby Ignoto » Tue Apr 08, 2014 11:24 am
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Re: Stages Power Meter
Postby GAV!N » Tue Apr 08, 2014 11:30 am
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Re: Stages Power Meter
Postby Xplora » Tue Apr 08, 2014 12:22 pm
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Re: Stages Power Meter
Postby kb » Tue Apr 08, 2014 3:14 pm
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Re: Stages Power Meter
Postby Carrots » Tue Apr 08, 2014 4:23 pm
I have two Stages on my two Giants which both have the inbuilt speed/cadence sensors in the rear stay. Given the stages measures Cadence I haven't worried about putting the magnets on the cranks arms, however still use the sensor for the speed with no issues what so ever.Ignoto wrote:So I just had a FSA meter fitted and the guys at the LBS told me they had to take the Garmin Speed/Cadence sensor off so that it wouldn't cause any interference. I figured it wouldn't be a problem as the Stages pulls the cadence anyway, but what about speed?
I know the wheel magnet was used instead of the GPS on the Garmin as it provides a more accurate figure (especially if you're riding in tree coverage). So was the figure my Garmin was getting from the GPS or does Stages somehow calculate the speed you're going as well?
Can imagine that a magnet attached to the crank arm could cause an issue given close proximity (butted against it).
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Re: Stages Power Meter
Postby you cannot be sirrus » Tue Apr 08, 2014 4:35 pm
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Re: Stages Power Meter
Postby boss » Thu Apr 10, 2014 12:14 pm
Pretty annoyed...
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Re: Stages Power Meter
Postby singlespeedscott » Thu Apr 10, 2014 12:39 pm
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Re: Stages Power Meter
Postby boss » Thu Apr 10, 2014 12:41 pm
I am about to build up a new, more or less 'dream bike' build... I am pretty lost as to what I'm going to do RE: a power meter. Dura Ace 9000 groupset with a Stages PM was pretty much the go... dunno now.singlespeedscott wrote:I have read nothing in here that would posses me to purchase a Stages power meter. They have a lot of R&D to perform IMO.
Depends how well the shop and distro deal with this issue now. I am half expecting to get a lecture about riding in the rain...
Might get some vector pedals but that will mean new pedals for all my other road bikes (switch to keo cleat).
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Re: Stages Power Meter
Postby singlespeedscott » Thu Apr 10, 2014 12:51 pm
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Re: Stages Power Meter
Postby Jesmol » Thu Apr 10, 2014 1:15 pm
Nobody has said you cant....singlespeedscott wrote:What's the point of a PM you can't use in the rain.
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Re: Stages Power Meter
Postby Crawf » Thu Apr 10, 2014 1:22 pm
Does chew through batteries, the last one lasted a month but that was a big month, I ordered a large dealextreme CR2032 batch for chump change so not bothered.
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Re: Stages Power Meter
Postby boss » Thu Apr 10, 2014 2:55 pm
Nobody has said that, in fact the Stages website says otherwise (see below)... but the fact of the matter is that when you ride in the rain (or on a wet road), the battery goes dead within a few days.Jesmol wrote:Nobody has said you cant....singlespeedscott wrote:What's the point of a PM you can't use in the rain.
I'm not one to stop riding when it rains, and I want power data for all my rides.
The battery is supposed to last 200 hours according to Stages. I haven't even got anywhere near 100 hours in 6 months of ownership. Nowhere near that.
Random dead batteries for a piece of hardware your paying ~$1000 on isn't right.
The fact that they stick a bunch of Vaseline in the battery compartment would indicate they knew this was a design flaw from the beginning.
I.e.
= bulls**tStages Website wrote:It can withstand the harshest down pours and being fully submerged in a stream crossing. However, it should not be put in a high pressure situations like being directly sprayed with a pressure washer or deep sea diving mountain biking.
As much as I hate to alter the silhouette of my bikes, and as much as I don't want to switch pedals on my two other bikes, I am becoming more at peace with switching to Garmin Vector pedals.
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Re: Stages Power Meter
Postby Jesmol » Thu Apr 10, 2014 3:00 pm
I've had occasional dead batteries as well, nothing to do with water though. I ride a crapload less then you, so its not hours. I suspect the unit is at times not going to sleep , maybe its picking up my phone BT or something, or if the bike is leant against a wall on the crank arm and it senses a load.boss wrote:Nobody has said that... but the fact is that when you ride in the rain (or on a wet road), it stops working!Jesmol wrote:Nobody has said you cant....singlespeedscott wrote:What's the point of a PM you can't use in the rain.
I'm not one to stop riding when it rains, and I want power data for all my rides. As much as I hate to alter the silhouette of my bikes, and as much as I don't want to switch pedals on my two other bikes, I am becoming more at peace with switching to Garmin Vector pedals.
The battery is supposed to last 200 hours. I haven't even got anywhere near 100 hours in 6 months of ownership. Nowhere near that.
Random dead batteries for a piece of hardware your paying ~$1000 on isn't right.
Last flat battery was found on my warm up for Sundays CS out at Woodside, great fun, lucky I carry a battery at all times.
Glad to see the battery cover was fully intact when I took it off though.
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Re: Stages Power Meter
Postby boss » Thu Apr 10, 2014 3:06 pm
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Re: Stages Power Meter
Postby you cannot be sirrus » Thu Apr 10, 2014 3:40 pm
My stages has had a piece of electrical insulation tape over the battery cover from day one just in case of water ingress problems. I'm on my second battery in 5 months and changed the first one before it died because I was doing a long ride and didn't want it to die mid ride.
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Stages Power Meter
Postby dale79 » Thu Apr 10, 2014 4:08 pm
Don't buy one then, it's pretty simple, buy garmin pedals and when you knock the pods off complain in another threadsinglespeedscott wrote:I have read nothing in here that would posses me to purchase a Stages power meter. They have a lot of R&D to perform IMO.
You buy a cheap meter you will have to deal with some form of shortfall. You want perfect buy a SRM..
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Re: Stages Power Meter
Postby toolonglegs » Thu Apr 10, 2014 4:39 pm
Disposable maybe... but not cheap .
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Re: Stages Power Meter
Postby boss » Thu Apr 10, 2014 4:40 pm
All well and good to say that, and I do side with your opinion (i.e. don't buy it if you don't wanna)...dale79 wrote:Don't buy one then, it's pretty simple, buy garmin pedals and when you knock the pods off complain in another threadsinglespeedscott wrote:I have read nothing in here that would posses me to purchase a Stages power meter. They have a lot of R&D to perform IMO.
You buy a cheap meter you will have to deal with some form of shortfall. You want perfect buy a SRM..
But when I'm sitting here, looking at the Stages website claiming both that the unit is 'waterproof' and has a 200 hour run time, and all the while my unit is chewing batteries like it's going out of business...
I mean we're past the point of saying "Well, you should have spent more and bought a SRM" and we're into the territory of false advertising, deception, etc.
Or to be blunt - I'm not complaining about the accuracy of the thing. I bought a Stages and accept that there are limitations in it's design with regard to accuracy. I'm (and others are, too) complaining about something much more simple than that - the expectation that I can take it for a ride rain/hail/shine and put it aside and then take it for a ride the following day. The Stages unit that I currently own does not fulfill that basic expectation.
I'd rather control the variable (knocking off a pod) than have something that is completely out of my control (either design flaw or quality control issue - take your pick).
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Re: Stages Power Meter
Postby dale79 » Thu Apr 10, 2014 4:41 pm
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