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PostPosted: Mon Mar 02, 2009 4:35 pm 
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I am sorry, but I think that it is a joke that Shimano Di2 does not have a power meter built into it. In fact all groupsets now should be integrating power meters into the cranks and controls of the group. It is the only way the technology will evolve.
SRM is the biggest joke in the electronics world. Technology that has barely evolved over the last decade, and it costs as much if not more than when it first came out.

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Posted: Mon Mar 02, 2009 4:35 pm 


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PostPosted: Mon Mar 02, 2009 4:47 pm 
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hockinsk wrote:
but you can't buy a Powertap 'without' the display.

Yes you can.

I have recently done it


/Håkan


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PostPosted: Mon Mar 02, 2009 5:24 pm 
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I know this thread is WAY off topic, so I will add to the offtopicness...LOL :lol:

When there is talk about PMs, I always hear that one is more accurate than another. PM companies seem to bragg about accuracy more than repeatability. Seems odd.

Does it matter if it is accurate or if it is repeatable numbers? Does it matter if the PM says your FTP is 280 or 500 as long as it is always the same number associated with the same ammount of strain/work? When you guys talk about accuracy; are you talking about repeatability or accurate power numbers? From books I have read, workouts seem based off of base numbers not how close that number is to your "real" power.

Couldn't a "new" PM company cut a lot of cost buy building a meter that has repeatability but not as accurate? Or do these have to go hand in hand?


Sorry for the dumb questions?


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PostPosted: Mon Mar 02, 2009 6:18 pm 
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Needs to be both. Repeatability is fine if you are training by yourself or only using it to pace your workouts and events. But they need to be accurate to compare one athlete to another unless you want to use the same powermeter.

Plus if its repeatable then it can usually be made to also be accurate. Its simply a matter of changing some number in the equation used to calculate power till the result is both repeatable and accurate. This or something similar can already be done with several powermeters on the market if accuracy is off.


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PostPosted: Mon Mar 02, 2009 6:50 pm 
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kytyree wrote:
Needs to be both. Repeatability is fine if you are training by yourself or only using it to pace your workouts and events. But they need to be accurate to compare one athlete to another unless you want to use the same powermeter.

Plus if its repeatable then it can usually be made to also be accurate. Its simply a matter of changing some number in the equation used to calculate power till the result is both repeatable and accurate. This or something similar can already be done with several powermeters on the market if accuracy is off.


Why would you need to compare to another rider? I can make less power than a 180lb guy and go much faster because I am 158lbs. Power from one rider can be totally different than another yet they will perform the same; right? Power should only matter to that particular rider. Numbers from another mean nothing your own #s.

Maybe I need to do some more reading. :lol:


Last edited by spinwax on Mon Mar 02, 2009 6:54 pm, edited 1 time in total.

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PostPosted: Mon Mar 02, 2009 6:53 pm 
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That's why they use watts per kg as one way to compare.


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 Post subject: Re: PMs
PostPosted: Mon Mar 02, 2009 7:08 pm 
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I guess WE like to compare the numbers amongst ourselves just for fun.

It personally doesn't matter to me if my powermeter is reading high or low. As long as I can do my testing and plan my programme based upon the same readings, it is all good. Where the system accuracy IS important to me is for the readings I get BETWEEN my systems. It is no good if the readings from the Roadbikes, TT and MTB are all different, for example. What I want in a PM is enough accuracy to 'ensure' that when I calibrate my systems using identical methodology and identical weights, that they all report the same power, within a reasonable range.


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PostPosted: Mon Mar 02, 2009 7:20 pm 
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kytyree wrote:
That's why they use watts per kg as one way to compare.



Got it, thanks!!!! Makes perfect sense. I didn't even think of that. I really want a PM. Should be soon. :wink:


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PostPosted: Mon Mar 02, 2009 10:09 pm 
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2 wheels wrote:

The system could possibly be mounted between the shoe and the cleat.


To have something mounted between shoes and cleat, wouldnt it give troubles with shoes height? I mean, sometimes cyclists choose pedals cause lower the shoes height, isnt it?

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PostPosted: Mon Mar 02, 2009 10:32 pm 
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spinwax wrote:
kytyree wrote:
Needs to be both. Repeatability is fine if you are training by yourself or only using it to pace your workouts and events. But they need to be accurate to compare one athlete to another unless you want to use the same powermeter.

Plus if its repeatable then it can usually be made to also be accurate. Its simply a matter of changing some number in the equation used to calculate power till the result is both repeatable and accurate. This or something similar can already be done with several powermeters on the market if accuracy is off.


Why would you need to compare to another rider? I can make less power than a 180lb guy and go much faster because I am 158lbs. Power from one rider can be totally different than another yet they will perform the same; right? Power should only matter to that particular rider. Numbers from another mean nothing your own #s.

Maybe I need to do some more reading. :lol:


One example is if you are a coach of a team and want to compare riders so you can select the best guys for a particular event.
Or if you want to predict your CdA.

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PostPosted: Tue Mar 03, 2009 12:52 am 
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kytyree wrote:
A match will be different for everyone but it refers to a hard effort having been made. Of course that varies with individuals but each individual has different matches.


The match concept is really more subjective than quantitative. The body does not have an integral number of discrete matches, to be spent one at a time. To quantify "matches" with high precision is sort of silly.

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PostPosted: Tue Mar 03, 2009 9:45 am 
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HakanC wrote:
hockinsk wrote:
but you can't buy a Powertap 'without' the display.

Yes you can.

I have recently done it


http://www.wiggle.co.uk/c/Cycle/7/Power_Training/

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PostPosted: Wed Mar 04, 2009 8:41 pm 
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spinwax wrote:
I know this thread is WAY off topic, so I will add to the offtopicness...LOL :lol:

When there is talk about PMs, I always hear that one is more accurate than another. PM companies seem to bragg about accuracy more than repeatability. Seems odd.

Does it matter if it is accurate or if it is repeatable numbers? Does it matter if the PM says your FTP is 280 or 500 as long as it is always the same number associated with the same ammount of strain/work? When you guys talk about accuracy; are you talking about repeatability or accurate power numbers? From books I have read, workouts seem based off of base numbers not how close that number is to your "real" power.

Couldn't a "new" PM company cut a lot of cost buy building a meter that has repeatability but not as accurate? Or do these have to go hand in hand?

Sorry for the dumb questions?


When the repeatability is worse the accuracy is also. When you claim an accuracy of 2% the meter should be accurate within that 2% error margin. Only after some time (months/years?) it will need to be calibrated again.
As other said you don't want to have a calibration error in your power meter. When you switch between 2 devices/bikes it should just give the same values, otherwise it is useless for training. But calibration errors aren't difficult to solve.

@Coolhand. I never said it was easy, but a powermeter isn't rocket science for sure.


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PostPosted: Fri Sep 25, 2009 6:04 pm 
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Brim Brothers recently made a new blog entry after visiting Eurobike 2009 and it confirms that their system is cleat based: http://www.brimbrothers.com/2009/09/eurobike-2009
Quote:
Eurobike 2009

... As we talked to people at the show it became clear that there’s great interest in power measurement among equipment companies. One concept prototype of a pedal based system was on display, and rumours of other pedal based ones were circulating. Measuring in the pedal seems to be flavour of the month. The more we found out about these the more we became reassured that our cleat based system is better. All the pedal based ones will still require the cyclist to either move the pedals between bikes or buy a pair of the measurement pedals for each bike they own.

On the other hand, our system will have all the measurement in the cleat and on the shoe, so absolutely nothing will need to be moved between bikes (except you, wearing your shoes). You won’t even need a cadence detection magnet on the frame. Measuring in the cleat also avoids the problems of trying to completely seal rotating parts against moisture, and of falling accuracy as bearings wear, so we know that we won’t have those problems. We’re confident that our system will tick more boxes for you than any systems based on wheel hubs, cranksets, bottom brackets or pedals.


Another point that became apparent to us at Eurobike is that the growth of ANT+Sport as the preferred wireless standard will continue. ANT is the wireless system used by most power measurement systems, and will be used by our system. Many of the ‘conventional’ bike computer companies we talked to told us they have ANT power display devices in development, so over the next 12 months we can expect a number of new display devices capable of working with ANT compatible power measurement systems. That’s good news for you, because you’ll have more choice.

In the Brim Brothers labs things are progressing. We’ve been examining the performance of our prototype, testing and analysing its behaviour and accuracy under various conditions. We’re now designing the next prototype iteration, which we hope will be very close to the final design. This version will be used for limited road tests. By the way, we get a steady stream of offers to help with testing, but at this initial test phase we’ll just be using a very small number of local test riders. We appreciate the offers we get from all over the world to help with the testing, but we won’t be doing wider testing until we get closer to the final product.

One thing you can be sure of – we won’t be launching the product until it’s real and is ready for use. No marketing hype here.

They must refer to O-synce ICYCLOPOWER E’SY POWER which was on display at Eurobike and MetriGear Vector which is discussed in this topic viewtopic.php?t=62804.


Last edited by 2 wheels on Fri Sep 25, 2009 6:25 pm, edited 1 time in total.

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Posted: Fri Sep 25, 2009 6:04 pm 


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PostPosted: Fri Sep 25, 2009 6:24 pm 
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Actually from a Scientific perspective, there is a difference between accuracy and precision.

High accuracy, but low precision:
Image

High precision, but low accuracy:
Image

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