1) How do you know any piece of measuring equipment is consistent?

2) How often do people have 2 PM's? It certainly occurs, and no doubt occurs at a much higher percentage here on ST, but to think this is a huge concern for most triathletes and cyclists is a bit overblown, IMO.

3) Again, how many people, in the triathlon and cycling population, spend time figuring out what their drag parameters?

As for myopic, I'd say your last two points are exactly that. Focusing on two, small percentages and extrapolating those requirements to the population overall.

And I've been using a PM since PT hubs had ugly yellow caps, so I am hardly "new" to them. For the vast majority of people that use them, consistency is indeed more more important obtaining objective standards (which are largly meaningless to the user anyway.).

YMMV....which is fine.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

"People who are new to PMs often make the "precision is more important than accuracy" claim. That's myopic."

I work in a metrology/calibration/product testing field and I couldn't agree more about the precision and accuracy statement. The word "precision" is very often missused here.

jaretj

 So a watt may be more or less then a watt just as long as the power mtr is consistent . You are good with that !


Thom

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Slowtwitch bitchist place on planet earth

By checking them.

I specifically and purposefully didn't say you had to have both PM's at the same time. At some point everyone's PM needs replacement. If they're not consistent how will you treat your historical data?

That they don't when it's so easy to do so is their choice.

Ah. OK, I stand corrected. Some people who are old to using PMs are myopic, too.

Nevermind. I just went back and read the OP and your first responses are absolutely correct. I read more into the post and thought he was looking for justification for choosing between the two types of systems.

For the record, though, my previous responses assumed a "known" state of properly functioning and calibrated systems according to the manufacturer's specs. Barring that known state, you are correct and all bets are off regarding what we're seeing on the display.

While your retorts were quite "clever" (or not), you did not really answer the questions, did you?

Later....

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

This word, variable, I do not believe it means what you think it means...

(just busting your stones, I understand your point very clearly)

Tom, you and Robert have both made this distinction. I don't think I completely get it, but maybe I do. The crank based systems measure at the "engine" so drive train variences are precluded from interfering. Simple enough. Why is a PT superior for field (load) testing? Suppose I'm comparing 2 positions. With the PT, I should be measuring the load, with a crank system I should be measuring the load plus drive train losses. The only way I see it mattering is if the drive losses vary depending on speed and gearing used. Or maybe, if drive loss is relatively constant (ie always approximately 10 watts instead of 1% of power, just to make up numbers as examples).

Well, that's exactly it: drive losses do vary with the chainring/cog combination being used. Here's a little discussion we had over on that uncensored forum:
http://www.wattagetraining.com/...pic.php?f=2&t=87

Here's a plot from that thread. The bottom panel tells you that the difference between the PT and the SRM varied with chainring and cog. BTW, that was a frankencassette: the cogs were placed so the chainline from the front to rear was mostly eliminated as a source of the variation.

Hmmm. Sometimes people can't tell the difference between getting an answer and understanding the answer they got. Evidently it's not a function of the length of time they've been using a power meter.

Yup....and sometimes people can tell when they are dealing with someone whose only goal is to prove how "smart" they are rather than engage in a discussion.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

The 10W was the result of the combination of a slightly misaligned hanger AND a bent pulley cage. I realigned the hanger and mounted a different rear derailleur and the losses got down to the 1-2W range.

BTW, I found the losses tended to be more of a fixed number rather than a percentage.

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http://bikeblather.blogspot.com/

1. Robert is not smart. He has seen smart people and he's not one of them.
2. The discussion is above you. Robert has some patience with that. Some.

Don't you need relatively windless conditions to do accurate drag tests? I virtually always have wind where I ride.

Yeah, I've been pretty lucky in the situations I've fallen into. I've known some pretty sharp folks.

Well, either calm conditions or else a way to measure the wind.

I've known guys who've gone out at midnight in mid-winter in order to find sheltered roads with no traffic. Brrrr. I don't have that much commitment. I have gone out just before dawn but that's mostly cuz I get up early anyway.