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PostPosted: Fri Sep 18, 2009 9:16 pm 
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The Stig wrote:
all I'm saying is that for me, I prefer measuring power at the wheel, net of any drivetrain/frictional losses...I'm looking at it from an automotive background/perspective, which I think is more accurate. Like I said...that's me. We're not quite on the same page as you're referring to raw wattage, while I prefer net wattage.


OK, but *why* do you prefer power output at the wheel? What do you mean by "more accurate"? I have a strong automotive background as well, and there are situations where I want to know power at the flywheel and others where I want to know power at the wheels. Why do you prefer power at the hub (not the wheel; you're still missing out on tire losses, of course)?

Thanks,

Jason


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Posted: Fri Sep 18, 2009 9:16 pm 


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PostPosted: Fri Sep 18, 2009 9:24 pm 
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If I'm interested in modeling bike-versus-speed, for example for doing field testing of aerodynamics, you want the power as downstream as possible, to avoid confounding effects from drivetrain loss variation.

If I'm interested in physiological condition or in physical effort or pacing, I want it at the pedal.

A real power weenie might therefore want both.

Dan

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PostPosted: Fri Sep 18, 2009 10:04 pm 
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+1 on the key factor of power measurment being repeatability.

Other than as another lockerroom 'measurment' contest, how often do you need to look at power numbers comparatively? I guess if you were travelling to a location you had never been to before and were wondering about gearing, it might be useful to have a local rider tell you 'I need x watts in 39x25 to climb that comfortably' and judge yourself accordingly.

As long as your powermeter is consistent from ride to ride, you can complete your monthly testing, create your training programme and execute properly.


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PostPosted: Fri Sep 18, 2009 11:34 pm 
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djconnel wrote:
A real power weenie might therefore want both.

Dan


And some of us do (for just those reasons).

g

p.s. i have seen some pretty measureable differences in drivetrain losses when things are optimized versus not. More than the Mr. Willett reported.


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PostPosted: Sat Sep 19, 2009 1:36 am 
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youngs_modulus wrote:
The Stig wrote:
all I'm saying is that for me, I prefer measuring power at the wheel, net of any drivetrain/frictional losses...I'm looking at it from an automotive background/perspective, which I think is more accurate. Like I said...that's me. We're not quite on the same page as you're referring to raw wattage, while I prefer net wattage.


OK, but *why* do you prefer power output at the wheel? What do you mean by "more accurate"? I have a strong automotive background as well, and there are situations where I want to know power at the flywheel and others where I want to know power at the wheels. Why do you prefer power at the hub (not the wheel; you're still missing out on tire losses, of course)?

Thanks,

Jason


I prefer power at the wheel is because I'm coming from an auto perspective, which I think is more "realistic" (excuse the term "accurate"). I think it would be fair to say that someone putting 300 watts of power at the wheel is a bit stronger than someone putting 300 watts at the pedal, wouldn't you say? I'm not taking into account other factors because that's another story. As for your last statement, the hub is the closest thing you could get to net power, unless you want to put the bike on a dyno and account for tire losses, etc... Like I said Jason, it's just me. :beerchug: Just prefer a bigger picture that's all....

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PostPosted: Sat Sep 19, 2009 2:26 am 
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bikemesenger wrote:
The Stig wrote:
3% maybe insignificant over a short distance but over long distances like stage racing, it could be mean the difference between winning and loosing...just like in motorsports, 1 or 2/10's of a second difference per lap is small, but over a race distance is significant. But that's just me....


But why does that matter if your hub based powermeter reads 3% lower then your crank based powermeter? As long as they are both reading consistently the same numbers it doesn't matter if one is reading the 3% drivetrain loss.


I'm looking at the bigger picture/equation...from an engineering point of view, you give your competition that 3% advantage, whether it be a reduction/increase in drag, downforce, top end power, mechanical grip, or anything for that matter, they will use it to their advantage and beat you with it...as the saying goes on this forum, hence it's name Weight Weenies, "every ounce counts". To a weight weenie, do you think a gram/ounce of weight here and there on their bike is insignificant? You take whatever advantage you can get, small or big, and use it to your advantage to beat your opponents. It's attention to details that will set you apart. That's why that 3% matters...Let's say you and I make 300 watts of power, you at the pedals and me at the hub, what's your conclusion? Will that 3% advantage I have matter to you? Maybe not, but it all depends on what perspective you are coming from...my 1 cent worth.... :beerchug: Nevertheless, I will say that it is the cleanest looking power meter solution I've seen... :thumbup:

Anyway, I think we might be going a bit off topic here...apologies to the thread starter...

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PostPosted: Sat Sep 19, 2009 3:03 am 
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The Stig wrote:
It's attention to details that will set you apart. That's why that 3% matters...Let's say you and I make 300 watts of power, you at the pedals and me at the hub, what's your conclusion? Will that 3% advantage I have matter to you?


This is where you lost me. If you and I both make 300 watts of power, me at the pedals and you at the hub, then you're making ~7-10 watts more than me. If we weigh the same, you're going to beat me up the hill--you make more power than I do. Conversely, if we both make 300 watts where the tire meets the road, who cares whether my powermeter calls that 310 watts and yours calls it 300 watts? The race official is going to call it a dead heat no matter where we measure our power.


The Stig wrote:
Maybe not, but it all depends on what perspective you are coming from...my 1 cent worth....



Oh hey--to each his own! Measure your power however you want...whoever trains more wins! Myself, I find posting to obscure web forums much easier than doing 3x3-minute interval sets at 105% of functional threshold power. Guess which I've spent more time on today. :) Seriously, this is a subject about which reasonable men can disagree. I was just curious about your thought process. Thanks for explaining.

Cheers,

Jason


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PostPosted: Sat Sep 19, 2009 3:08 am 
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gregclimbs wrote:
i have seen some pretty measureable differences in drivetrain losses when things are optimized versus not. More than the Mr. Willett reported.


Ooh! Care to share your data? That sounds interesting!

Cheers,

Jason


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PostPosted: Sat Sep 19, 2009 3:17 am 
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I am amazed that these net vs gross arguments do not rear their ugly head when the infallible superiority of an SRM comes up in a thread. I think people just want to throw stones at new concepts.


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PostPosted: Sat Sep 19, 2009 3:55 am 
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youngs_modulus wrote:
...why does this device have an accelerometer at all? I know in a previous post I mentioned getting cadence as a function of time, but now I'm not sure that's such a good idea. These accelerometers are going to be very small, and their natural frequency will be quite high. They'll be picking up all sorts of extraneous stuff, and you'll have to do a fair amount of signal processing to filter it out. After all that, the velocity number you get may not be any more accurate (or any higher resolution) than a simple chainstay pickup. So why include accelerometers?



Your quandry and mine may be related - I was wondering how they would filter out torque applied to the pedals when simply coasting with all (okay most) body weight on the pedals. ie. When standing out of the saddle on the pedals coasting, with the cranks at 6&9 o'clock, and you roll over a bump - what does it do with the torque from both spindles?

Perhaps the accelerometers help with filtering that 'noise'...?


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PostPosted: Sat Sep 19, 2009 4:39 am 
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I like that this system is non-intrusive and can be pretty much attached onto any bike easily. Changing out cranks for a SRM or Quarq is a pain, and changing a powertap wheel about is annoying. I look forward to buying a set of these when they become available.

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PostPosted: Sat Sep 19, 2009 4:45 am 
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vladav wrote:
Your quandry and mine may be related - I was wondering how they would filter out torque applied to the pedals when simply coasting with all (okay most) body weight on the pedals. ie. When standing out of the saddle on the pedals coasting, with the cranks at 6&9 o'clock, and you roll over a bump - what does it do with the torque from both spindles?


Power = torque × angular velocity (2 π / instantaneous cadence). If you're standing on the pedals, this will be effectively zero. If the pedals are moving a bit, the forces will be in equal and opposite directions, and you'll get a positive power on one pedal offset by a negative power on the other.

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PostPosted: Sat Sep 19, 2009 4:48 am 
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So a question I want to ask, does the preliminary info and design pass djconnel's approval? DJ, do you think this could be a winner?


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PostPosted: Sat Sep 19, 2009 5:22 am 
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tranzformer wrote:
So how does this compare to the ICYCLOPOWER: E’SY POWER? Basically same idea?

New power meter: http://www.o-synce.com/en/cyclometer-power.html
ICYCLOPOWER: E’SY POWER

ICP enable to measure the exact vertical & horizontal power the biker is using on the pedal. It‘s the only solution in the world which can be easily mount w/o complicated tools or knowledge, can be changed to any kind of bicycle in a few minutes and will be able to get:
    • an exact power measurement over the crank set angle position.(biomechanical analyzing)
    • enable to a comparison of power with each leg (performance optimization)
    • utilizate the aerodynamic drag force (to optimize to the most economic position on the bike -aerodynamic in relation to biomechanical movement) Combinable with the MACRO X series. Available mid of 2010.

Image
[/quote]

This one has me a bit more interested, as it looks like we wouldn't be limited to Speedplay pedals.

I prefer Time, myself - and I wouldn't consider switching to Speedplay just for a particular power meter.

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Posted: Sat Sep 19, 2009 5:22 am 


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PostPosted: Sat Sep 19, 2009 5:36 am 
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youngs_modulus wrote:
gregclimbs wrote:
i have seen some pretty measureable differences in drivetrain losses when things are optimized versus not. More than the Mr. Willett reported.


Ooh! Care to share your data? That sounds interesting!

Cheers,

Jason


Here is just some of it...

http://wattagetraining.com/forum/viewtopic.php?f=2&t=87

That is not a complete set of the information, but one of the ways to "optimize" the drivetrain. There are others. FWIW, the drag of the freehub on my zedtech sub9 has more friction than the rest of the drivetrain on my tt bike... spin the rear wheel on the stand and the cranks spin...

g


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