Stages Power Meter

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Re: Stages Power Meter

Postby dale79 » Mon Aug 12, 2013 12:11 pm

Do you think anything is going to be accurate with only 1 leg peddling?? Especially with sample rates at best 1sec.. So you get 1 sample at 200w then the next is 0 then 50 because it was at the bottom of the stroke etc.. Ie pointless data unless using both legs

im used to using equipment that samples at up to 1000 times a second for data capture. the first thing I noticed when using a quark or powertap was how slow they sample and how hard it makes it to get nice smooth data..

my data recording equipment on my race cars I sample the most simple things like ignition timing or transmission pressure etc at 20 times a second and things like engine rpm, drive shaft rpm etc are sampled at minimum 100 times a second to give accurate data,
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by BNA » Mon Aug 12, 2013 12:55 pm

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Re: Stages Power Meter

Postby dalai47 » Mon Aug 12, 2013 12:55 pm

dale79 wrote:Do you think anything is going to be accurate with only 1 leg peddling?? Especially with sample rates at best 1sec.. So you get 1 sample at 200w then the next is 0 then 50 because it was at the bottom of the stroke etc.. Ie pointless data unless using both legs


Pointless but not inaccurate... The torque sampling rate is higher at 200Hz for the SRM compared to 60Hz for the Quarq and similar for the Powertap.
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Re: Stages Power Meter

Postby dale79 » Mon Aug 12, 2013 12:56 pm

Try telling your garmin or other device to log it at 200hz or even 60hz..
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Re: Stages Power Meter

Postby dalai47 » Mon Aug 12, 2013 1:08 pm

Interval of storage on the SRM head unit can be set as low as 0.1 sec.
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Re: Stages Power Meter

Postby dale79 » Mon Aug 12, 2013 1:22 pm

dalai47 wrote:Interval of storage on the SRM head unit can be set as low as 0.1 sec.


once again comes back to this
stages DA 9000 $900USD vs SRM DA9000 with display $3895USD. so $3000USD more.
for a extra $3000 you would want to get something a little extra, but your still only recording data at .1sec which is only 10hz not 200hz
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Re: Stages Power Meter

Postby Xplora » Mon Aug 12, 2013 1:28 pm

dale79 wrote:
dalai47 wrote:Interval of storage on the SRM head unit can be set as low as 0.1 sec.


once again comes back to this
stages DA 9000 $900USD vs SRM DA9000 with display $3895USD. so $3000USD more.
for a extra $3000 you would want to get something a little extra, but your still only recording data at .1sec which is only 10hz not 200hz

And poor Takai's buggered knee is going to render 90% of his power training (TSS, CP, blah blah blah) virtually useless because he's not putting out any intervals with one leg pedalling on the bike.

Talk about SRM is pointless. SRM isn't competing with Stages, or even Quarq with the improved sampling etc. Fiat isn't competing with Ferrari even though they both make small Italian two door cars :idea: It's particularly pointless given that comparison was already ruled out of the discussion before as a basis for argument.
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Re: Stages Power Meter

Postby dalai47 » Mon Aug 12, 2013 1:46 pm

Unless you go second hand. Over the years wired units have been coming considerably down in price. Last road unit I bought (FSA K Force) cost me $630 complete a couple of years ago. I've seen SRM Pro and now even dura ace 7800 go for around the $500 mark!
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Re: Stages Power Meter

Postby dale79 » Mon Aug 12, 2013 2:19 pm

7800 awesome.. so you buy a new bike with the latest 11 speed group set and then swap out the cranks to some 6 year old ones.. sounds great,

also just been informed that the sample rate on the SRM is actually 4hz or .25 of a second.. that's 4 times a second not 200 times a second...
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Re: Stages Power Meter

Postby dalai47 » Mon Aug 12, 2013 2:57 pm

Are you sure the sample rate is 4Hz? The unit does send 4 data packets per second via Ant+

As to matching kit - I'd much rather a PM that has the accuracy to not just be a data logger used to calculate TSS...
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Re: Stages Power Meter

Postby dale79 » Mon Aug 12, 2013 3:15 pm

dalai47 wrote:Are you sure the sample rate is 4Hz? The unit does send 4 data packets per second via Ant+

As to matching kit - I'd much rather a PM that has the accuracy to not just be a data logger used to calculate TSS...



4 data packets a second is 4hz, weather it calculates a average every 1/4 second and then sends that makes no difference its still only 4 times a second,

what is actually accurate? which one is right? I have a $90,000 piece of equipment that measures power on cars, but it measures differently to the one around the corner, so which one is right and which one is wrong? with them all being with in 1-2% of each other in the reports that have been done so far that accuracy is close enough.
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Re: Stages Power Meter

Postby Xplora » Mon Aug 12, 2013 4:28 pm

dalai47 wrote:Unless you go second hand.

Cmon dude... that's just grasping at straws. You cannot buy 11 speed power meters from anyone for 500 bucks... unless you got a used Stages :roll:

Find me some used power meters that match the 11 speed gear at 500 bucks. Not everyone wants to buy clapped out second hand gear either. (TONS of people seem to be very disinterested in second hand power meters from my reading).

SRM doesn't compete with Stages. At any level. I would love it if Stages could rejig their stuff and match the 4hz sampling etc, but again... it's horses for courses. Maybe I've drunk too much coffee today, but this debate is beyond ridiculous.
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Re: Stages Power Meter

Postby dalai47 » Mon Aug 12, 2013 4:42 pm

Look, I'm not anti Stages; actually happy to see more options come to market including this one. If I didn't already have a PM, I would definitely consider the Stages unit as it ticks quite a few boxes.

All PM's have Pros and Cons - just keeping people minds open to other options available...

As to accuracy - when Alex and Robert Chung (thanks to Robert one of the firmware updates was made to fix an issue he found examining Stages data) suggest the Stages isn't accurate enough for field testing I listen to them. Having spent $$$ for time in the wind tunnel a while back, owning a PM that is deemed accurate enough to perform field testing to test position or equipment changes is invaluable.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 5:06 pm

dale79 wrote:you will establish a power profile and be able to train no problems at all, anything you can do with a powertap you can do with a stages.. despite what some people will say..

There are many things you can do with power meters and their data, and some of those things the data from a Stages will be adequate, but there are some things that require a greater level of precision and accuracy than the Stages can provide.

Please, don't make a claim from ignorance of how power meters and their data can be used.

dale79 wrote:go read DCrainmakers review, the power outputs coming from the 4 meters on his bike

One rider's data over a couple of rides does not tell me about the quality of Stages data over longer term nor the relative variances that may occur for a different rider. Although I note his recent reviews were about the Garmin Vector than the Stages.

Ray posted a little more data in last day. djconnel notes when inspecting the extra data that there is good agreement between Stages and Vector left pedal, but not as good agreement with Vector right pedal power (which is to be expected).

dale79 wrote:are with in a few % of each other which unless you are a elite pro will be good enough.. remember all you need is consistent readings, doesn't really matter if you are reading a couple of % high or low..

Again, that depends on the purposes for which you seek to use the power meter. This is really important distinction to make. Please do not make the assumption that the level of accuracy or precision which satisfies your needs, will be sufficient to satisfy everyone else's needs.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 5:06 pm

winstonw wrote:does anyone want to spell out what a non elite, non NRS cyclist is going to use a power meter for, then explain why a Stages is inadequate for the purpose?

I'll start:
At some stage I will buy and train with a power meter. I'll use it to
1. establish a power profile, then tweak my training to optimize the profile.
2. facilitate race performance by avoiding blowing up.

At my age and with my musculoskeletal history, I know the difference I can make to L/R power variation is minimal.

I'd say that for the purposes you've outlined (which are some or the least demanding applications of power meter data), a Stages (provided it meets your budget and durability/reliability requirements) will be adequate, excepting for the short duration / peak power end of your power profile (but I don't know how important such information is to you, nor whether that's an element of performance improvement in your power profile you may be seeking to specifically target).
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Re: Stages Power Meter

Postby Xplora » Mon Aug 12, 2013 5:13 pm

Reason for the short duration CP issues?
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 5:22 pm

dalai47 wrote:Interval of storage on the SRM head unit can be set as low as 0.1 sec.

Only on older SRMs using a power control IV or V can the recording rate be set as high as 10Hz.

SRMs using a PCVI or PC7 have a maximum recording rate of 2Hz.

However even that is significant when considering an application such as when testing maximal pedal force - pedal velocity capabilities, for which 2Hz is sufficient.

One cannot do such assessment with a Powertap (due to time based torque sampling and associated data aliasing, and the 1Hz recording rate), nor a Quarq (due to inconsistencies in torque sampling response in such situations, as well as the 1Hz recording rate). You certainly can't do it with a Stages. The Power2Max and Garmin Vector are yet to be tested in their capability on this front (I've asked the question), although 1Hz recording rate doesn't help when the onset of fatigue during such testing occurs after 5-6 seconds.

Again, whether such an ability to do this, or other data demanding things (e.g. aerodynamic and rolling resistance testing) is important to any individual will vary.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 5:26 pm

dalai47 wrote:As to accuracy - when Alex and Robert Chung (thanks to Robert one of the firmware updates was made to fix an issue he found examining Stages data)

Credit to Stages for fixing a problem clearly articulated by Robert's analysis, and which improved the quality of data for all Stages users.

Discredit to Stages for rubbishing Robert for doing the analysis which pointed this out this flaw to them.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 5:36 pm

dale79 wrote:
dalai47 wrote:Interval of storage on the SRM head unit can be set as low as 0.1 sec.


once again comes back to this
stages DA 9000 $900USD vs SRM DA9000 with display $3895USD. so $3000USD more.
for a extra $3000 you would want to get something a little extra, but your still only recording data at .1sec which is only 10hz not 200hz

Just a couple of corrections for the record.

If you compare prices, then don't compare one with a head unit to one without. The difference to an Aussie between a DA Stages and DA SRM will be a bit over $2k. I make no value judgement, just pointing out the over statement of SRM pricing.

There is a big difference between the torque sampling rates (typically ranging from 60 to 500Hz depending on model), and the recording rate of power data by head units (from 0.2 to 10Hz depending on model).

There are clear advantages to a higher torque sampling rate and high higher recording rates, however that in and of itself doesn't mean a meter will be more accurate. Just look a the inconsistent mess of inaccurate data that Rotor's power meter (which samples at 500Hz) is presently providing.
Last edited by Alex Simmons/RST on Mon Aug 12, 2013 5:37 pm, edited 1 time in total.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 5:37 pm

dale79 wrote:also just been informed that the sample rate on the SRM is actually 4hz or .25 of a second.. that's 4 times a second not 200 times a second...

Your informer is wrong.
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Re: Stages Power Meter

Postby dale79 » Mon Aug 12, 2013 5:43 pm

Alex Simmons/RST wrote:
dale79 wrote:you will establish a power profile and be able to train no problems at all, anything you can do with a powertap you can do with a stages.. despite what some people will say..

There are many things you can do with power meters and their data, and some of those things the data from a Stages will be adequate, but there are some things that require a greater level of precision and accuracy than the Stages can provide.

Please, don't make a claim from ignorance of how power meters and their data can be used.

dale79 wrote:go read DCrainmakers review, the power outputs coming from the 4 meters on his bike

One rider's data over a couple of rides does not tell me about the quality of Stages data over longer term nor the relative variances that may occur for a different rider. Although I note his recent reviews were about the Garmin Vector than the Stages.

Ray posted a little more data in last day. djconnel notes when inspecting the extra data that there is good agreement between Stages and Vector left pedal, but not as good agreement with Vector right pedal power (which is to be expected).

dale79 wrote:are with in a few % of each other which unless you are a elite pro will be good enough.. remember all you need is consistent readings, doesn't really matter if you are reading a couple of % high or low..

Again, that depends on the purposes for which you seek to use the power meter. This is really important distinction to make. Please do not make the assumption that the level of accuracy or precision which satisfies your needs, will be sufficient to satisfy everyone else's needs.


ok mate, go back to selling your $3000 power meters that are clearly the worlds best things and leave the people who want data for under $1000 to work out weather they like it or not, you are clearly butt hurt that these meters will take your sales and are trying to do everything you can to stop it,

people that are looking at the cheaper end of the scale do know that there are some limits to the meters and the data wont be as refined as the more costly units that's pretty normal when it comes to cheap vs exxy products..
im done here and ill keep my findings on my stages meter to my self and my mates because no matter whats posted here some people will just want to pick it to pieces because they feel the need to make the cycling world think they are the king of training and power..
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 5:50 pm

Xplora wrote:Reason for the short duration CP issues?

CP?

Critical Power? There is only one critical power and it's "for a long duration" but typically thought of as power sustainable for about an hour.

If you mean peak power testing, well it sort of depend on what you are testing for. There a difference between testing peak power simply to know what it is*, and testing the components of peak power to assessing what training is better to focus on in order to improve.

* which SRM, Quarq, Powertap are OK for, although Powertap is more prone to error for very short durations, and a Stages simply suffers from measuring one crank only and maximal effort is where such imbalances will be their greatest, and probably least consistent. I have inufficient data to properly assess Power2Max on this front.
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Re: Stages Power Meter

Postby dalai47 » Mon Aug 12, 2013 6:04 pm

That is extremely poor comment dale79. I have always found Alex has always been unbiased in his comments including about Quarqs when he wasn't selling them. He has given clear and accurate reasoning given to false statements made in this topic. Unfortunately you are not willing to see this and we will all be the poorer for it if your comments means Alex is less likely to post online and give out information freely!

You are wearing rose tinted glasses about the Stages unit since you have dropped coin on it! There are limitations with measuring power on one side. You continually ague there isn't. If you don't believe Alex, there are journal articles written on the subject supporting the issues with L/R imbalance.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 6:16 pm

dale79 wrote:ok mate, go back to selling your $3000 power meters that are clearly the worlds best things and leave the people who want data for under $1000 to work out weather they like it or not, you are clearly butt hurt that these meters will take your sales and are trying to do everything you can to stop it,

people that are looking at the cheaper end of the scale do know that there are some limits to the meters and the data wont be as refined as the more costly units that's pretty normal when it comes to cheap vs exxy products..
im done here and ill keep my findings on my stages meter to my self and my mates because no matter whats posted here some people will just want to pick it to pieces because they feel the need to make the cycling world think they are the king of training and power..

Chill dale79, not sure why you seem upset/annoyed/taking an on topic discussion so personally.

I'm completely OK with people buying whatever they like, no skin off my nose. I'm happy you are happy with your meter, that's great and I wish you well. Use it wisely and I'm sure you can improve lots and enjoy the process.

And if it isn't already obvious from my responses here, I've made it clear that (subject to reliability, durability etc since it is in its "early stages" - pardon the pun), the Stages looks a suitable option for many considering getting into power measurement, and it looks like it will satisfy the data quality requirement of many, but not all. What I am doing is help to qualify such issues so that people can make an informed choice, or would you prefer people make choices on the basis of ignorance and misinformation (some of which I have corrected in this thread)?

If you wanted to know, I'd happily point out good points and flaws with any power meter (they all have them), SRM included. But this is the Stages thread, so I see no problem in discussing matters pertaining to the Stages power meter. It is completely on-topic.
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Re: Stages Power Meter

Postby Alex Simmons/RST » Mon Aug 12, 2013 7:00 pm

Alex Simmons/RST wrote:
dale79 wrote:also just been informed that the sample rate on the SRM is actually 4hz or .25 of a second.. that's 4 times a second not 200 times a second...

Your informer is wrong.

I made an error in assuming your informer was wrong when it is your interpretation of what you were informed that's wrong.

SRMs (and most ANT+ power meters) transmit data packets to head units at 4Hz, but that is not the torque data sampling rate (200Hz for SRMs), nor the data recording rate (up to 2Hz for a Powercontrol or 1Hz for Garmin or other ANT+ head units).

Of course, SRMs calculate power based on variable duration samples that are event based*, and not time based samples (like a Powertap).

* and uses the whole number of completed crank revolutions since last reported sample.
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Re: Stages Power Meter

Postby dalai47 » Mon Aug 12, 2013 9:18 pm

@Xplora No grasping at anything. Many people opt to buy second hand - all three SRM's I own were all bought second hand. None are 'clapped out'. :roll:

As to 11 speed. My SRM Pro is 11 speed - My Stronglight chainrings are 10-11speed capable. Do you think cranksets are that discerning?
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