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-   -   Stages Track Power Meter Review (http://www.bikeforums.net/track-cycling-velodrome-racing-training-area/923063-stages-track-power-meter-review.html)

carleton 11-21-13 07:39 PM

Here's a f200m on a 250M track

http://giovannirey.blogspot.com/2009...d-numbers.html

http://i.imgur.com/kAFVMJ9.jpg

Dalai 11-22-13 04:47 AM

Quote:

Originally Posted by Impreza_aL (Post 16266385)
i'm too attached to my campy. since i don't train at the track the motivation to get one is pretty low. i would just like to see what kind of power i put out during a mass start race.

Other options except DA Impreza_aL. For road though there are quite a few options for only a fraction more than the Stages unit that I would recommend more.

Quote:

Originally Posted by carleton (Post 16266297)
I just found out that the newest SRM Powercontrol 7 head unit will record 4 times per second! That's 49 (48+1) samples for a 12" flying 200M.

But, it costs $950 :(

PC8 is due out very soon, So I am holding out for a PC7 for a recently purchased used wireless road SRM when everyone upgrades... No interest in upgrading my wired track SRM though. But I am an enduro so am fine with 0.5 second sampling.

Quinn8it 11-22-13 11:01 AM

Quote:

Originally Posted by Dalai (Post 16267987)
Other options except DA Impreza_aL. For road though there are quite a few options for only a fraction more than the Stages unit that I would recommend more.

that's a bit of an exaggeration..

yes PowerTap lowered their price and brought it into the range of Stages- but that limits you to one wheel, which is an issue if you train and race on different wheels. plus the lower priced complete wheels are not high performance and the higher end wheels are quite a bit more expensive. building the Hub on your own rim creates problems as PowerTap only accepts warranty returns on the part they sold you- so a returned Hub would have to be unlaced before sending it back.

what other options are "a fraction more"?

if you are saying there are used options- that's comparing apples to oranges..

as for the older used wired SRM units. I have one and think it is great, its on my Ergo, but SRM recently announced they are ending their service period on these units, making them a much less viable option

slindell 11-22-13 01:44 PM

Quote:

Originally Posted by Quinn8it (Post 16268871)
yes PowerTap lowered their price and brought it into the range of Stages- but that limits you to one wheel, which is an issue if you train and race on different wheels. plus the lower priced complete wheels are not high performance and the higher end wheels are quite a bit more expensive. building the Hub on your own rim creates problems as PowerTap only accepts warranty returns on the part they sold you- so a returned Hub would have to be unlaced before sending it back.

Powertap works ok if you have a wheel you like. They repair by replacing the hub internals so as long as you are willing to ship a full wheel there is no need to unlace. The new hubs look like they moved the electronics to the cap so some repairs are likely just sending the cap back.
I just use the powertap for training, racing is what it is and looking at power numbers from mass start races they are pretty close to the guess by the internal power meter.

The Stages does look like a nice simple option and fast sampling can help with accuracy. If the head unit is collecting at a different frequency it would be good to know what is being sent - average of last n samples or the last 1/64th of a second if 64 sends/sec. SRM is the last full crank revolution and I am guessing the others are similar. Rapid acceleration this can skew results a bit as it is torque * cadence as seen with non-round chainrings.
You do need to look at the auto calibration which is an issue with some head units and also where do they start reading. SRM wireless starts 30 rpm at least on the road so you miss the first couple of revs out of the blocks but this is where the faster reading might help a bit. I think Quarq and Stages are similar.

Dalai 11-22-13 02:57 PM

Not sure of pricing in the US, but Power2Max (V2 where they fixed the slope drift) is only a couple hundred more than the Stages here. The Vectors are already being discounted and is drifting closer to the $1000 mark are a couple options. Powertaps also work but like all the options has limitations.

I was including used units also... Why used not comparable? My SRM's were all bought second hand and have worked flawlessly... My latest SRM is an FSA wireless model that I bought from ebay cost US$800. Personally I'd rather used than V1 of an electronic product; every Powermeter player has had teething problems in the first round.

Interested to see a link about SRM ending their service period on the wired models as I hadn't heard that. You could still buy new the wired Track cranks with PCV so would expect them to support this? Not too fussed if they do though as battery replacements are easy enough and 99% time that is all they require when I've sent mine off for servicing.

Dalai 11-22-13 11:30 PM

Don't misunderstand me either Quinn8it. I am not anti Stages and appreciate your review - being a power junkie (now own 4 SRMs :twitchy:) I am keen to look at a Stages in the future for my MTB...

But given the suggested limitations with measuring one side only and doubling the data due to fluctuations with L/R balance across efforts and fatigue levels, one really beneficial use of a power meter is not possible; that of field testing aerodynamics. I have spent a day in the wind tunnel years ago and found the wattage savings amazing. I can't afford to go into the tunnel everytime the UCI forces us to change equipment or when I try something new with my position or equipment!

As an aside - first issue I have had with one of my wired units was on returning from the States recently was the coil broken in numerous places. Not sure how the luggage handlers managed it as the bike was well packed in the case. Local guy checked it over suggesting it was the circuit board so it was sent to NZ (we don't have a service center in Australia :notamused: ). Something not necessarily advertised as they would rather have you buy a new unit, but with some wired units they can swap in a wireless circuit board...

Quinn8it 11-23-13 12:50 AM

Quote:

Originally Posted by Dalai (Post 16270889)
Don't misunderstand me either Quinn8it. I am not anti Stages and appreciate your review - being a power junkie (now own 4 SRMs :twitchy:) I am keen to look at a Stages in the future for my MTB...

But given the suggested limitations with measuring one side only and doubling the data due to fluctuations with L/R balance across efforts and fatigue levels, one really beneficial use of a power meter is not possible; that of field testing aerodynamics. I have spent a day in the wind tunnel years ago and found the wattage savings amazing. I can't afford to go into the tunnel everytime the UCI forces us to change equipment or when I try something new with my position or equipment!

I understand that theoretically this is an inferior system- but I'm just not seeing any problem from it in real world applications

Dalai 11-23-13 08:06 AM

Quote:

Originally Posted by Quinn8it (Post 16270966)
I understand that theoretically this is an inferior system- but I'm just not seeing any problem from it in real world applications

Have you used it for anything other than just recording training? My field testing example above is one use where reliable data is required...

Quinn8it 11-23-13 10:19 AM

Quote:

Originally Posted by Dalai (Post 16271277)
Have you used it for anything other than just recording training? My field testing example above is one use where reliable data is required...

are you talking about something like Golden Cheetah AeroLab? no i have not used anything like that- but i am interested...

i do think you are making an assumption that the data from Stages is "unreliable"... im not convinced it is

Dalai 11-23-13 10:07 PM

No assumption - enough studies have shown asymmetry in power production.

http://www.ncbi.nlm.nih.gov/pubmed/17369798
http://www.ncbi.nlm.nih.gov/pubmed/10460126
http://www.ncbi.nlm.nih.gov/pubmed/21055708
http://www.ncbi.nlm.nih.gov/pubmed/979569

Everyone will have a different L-R power balance. It's also well established that asymmetry is also variable and will vary with:

-power output, absolute and/or relative
-fatigue
-cadence (or torque)
and likely a few other factors such as bicycle position, seated v standing and so on

So the Stages is a useful tool to measure power output to calculate TSS and track training progress. But due to variability in the resultant power calculated it has been commented as not accurate enough to be used in calculating CdA. Aerolab is one method (utilizing Chungs model) and Regression modeling another.

Quinn8it 11-23-13 10:33 PM

Quote:

Originally Posted by Dalai (Post 16272962)

So the Stages is a useful tool to measure power output to calculate TSS and track training progress. But due to variability in the resultant power calculated it has been commented as not accurate enough to be used in calculating CdA. Aerolab is one method (utilizing Chungs model) and Regression modeling another.

interesting!

thats too bad- i was going to try to figure out how to use aerolab and run some test..

Dalai 11-23-13 10:57 PM

Still worth trialling. I am only going on comments by Coggan and others in various forum posts about the Stages units...

Quinn8it 11-23-13 11:01 PM

yes- and i probably will.

i dont want to derail this thread- so maybe i will start another with some questions about using AeroLab..

Dalai 11-24-13 04:06 AM

In case you don't - here are a few worthwhile links to get you started.

www.timetriallingforum.co.uk/index.php?showtopic=81745

From the link above - https://www.dropbox.com/s/zwbs351x4u...ab%20V1.02.pdf

Also from AndyF who coded aerolab.

http://forum.slowtwitch.com/gforum.c...t_reply;so=ASC

carleton 11-25-13 11:52 AM

Quote:

Originally Posted by Dalai (Post 16272962)

Everyone will have a different L-R power balance. It's also well established that asymmetry is also variable and will vary with:

-power output, absolute and/or relative
-fatigue
-cadence (or torque)
and likely a few other factors such as bicycle position, seated v standing and so on

I agree.

Victoria Pendleton has a noticeable imbalance in her pedal stroke when she's coming into the final stretch of a Keirin/Sprint and she has to fight to win. She seems to muscle-over with her right leg and it makes her upper body do a rhythmic asymmetric wobble that is similar to what one would do in a one-legged drill.

You can't see it in all of her videos. Maybe she has changed it on the latter years of her career. But, I've seen it. Find a video of her having to fight to win (like coming around a fast opponent to win a keirin) and you'll see it.

JMR 11-26-13 07:37 AM

How many crank rpm do you need to reach before the Stages pm will give a reading?

I've heard that the Garmin Vector needs to be above 30 rpm... Which is not good for standing start efforts.

JMR

Brian Ratliff 11-26-13 11:34 AM

Talking about sampling rate and data transmission rate...

There are two things here. One is sampling rate. All powermeters sample at a very high rate so they get a good picture of power as the cranks go round. This is how the powertap calculates cadence, after all. When a powertap is said to record every 1.x seconds, it means there are many 10s of data points going into that recorded number. To put these numbers in perspective, at 90rpm, there is 1.5 pedal revolutions ever second. At 120rpm, there are two pedal revolutions every second. What you want recorded depends on what you are trying to measure.

If you are trying to record and keep track of average power over the whole pedal stroke (generally what most people want), then you record at a frequency less than 1 per second. That way, even at 75 or 80rpm (climbing cadence), you are getting readings that are averages throughout the entire pedal stroke and you are not recording torque pulse. If you are over 120rpm for the effort, then 0.5 seconds is appropriate, as this is probably the fastest frequency you can record power and still get an average over the pedal stroke.

Now, if you are willing to sort through the torque variation intra-pedal stroke, then you need to be recording at a much higher frequency than 2Hz (0.5 seconds per reading). You need at least, probably, 4 readings per pedal stroke to avoid serious aliasing, and probably would want several 10's of data points per pedal stroke to get really useful data. Now, the powermeter is likely already processing this, it is just a matter of recording all that data in hard memory. For a track cyclist working on standing starts, this is worth it. For a roadie or enduro, it is a lot of extra data which will burn through a lot of memory and battery life.

There is a dead zone between 1 and 4 readings per pedal stroke (at 120rpm, this would be between 0.5 and .125 seconds per reading), where the extra data you obtain is useless because of aliasing. You need at least enough data to resolve the duel torque pulses (one each leg) per crank revolution to gain anything from the extra data.

Brian Ratliff 11-26-13 11:40 AM

Quote:

Originally Posted by carleton (Post 16276792)
I agree.

Victoria Pendleton has a noticeable imbalance in her pedal stroke when she's coming into the final stretch of a Keirin/Sprint and she has to fight to win. She seems to muscle-over with her right leg and it makes her upper body do a rhythmic asymmetric wobble that is similar to what one would do in a one-legged drill.

You can't see it in all of her videos. Maybe she has changed it on the latter years of her career. But, I've seen it. Find a video of her having to fight to win (like coming around a fast opponent to win a keirin) and you'll see it.

My teammate says I do something similar; I think it is common to most sprint athletes. Watching football, you can certainly see a good number of running backs and receivers who, when they are really accelerating, have an extreme asymmetry to their stride.

Quinn8it 11-26-13 11:46 AM

Whoah!
Great stuff Brian! Thanks for that.


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