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-   -   Power Meter (http://www.bikeforums.net/road-cycling/944595-power-meter.html)

gregf83 04-24-14 07:41 AM

Quote:

Originally Posted by Gramercy (Post 16698082)
So you have 2 powermeters on one bike? Is that possible? Or am I missing something?

Crank & hub based meters.

canam73 04-24-14 07:45 AM

Quote:

Originally Posted by Gramercy (Post 16698082)
So you have 2 powermeters on one bike? Is that possible? Or am I missing something?

Have you ever read one of DCRainmaker's reviews? This is how he rolls:

http://www.dcrainmaker.com/images/20...erobars-11.jpg

lsberrios1 04-24-14 08:07 AM

Quote:

Originally Posted by Gramercy (Post 16698082)
So you have 2 powermeters on one bike? Is that possible? Or am I missing something?

That was just a silly joke :) I run a Quarq on my Roubaix and a PT on my TCR. However, I could run both since one is crank based and the other one is a hub.

RChung 04-24-14 08:24 AM

Quote:

Originally Posted by gregf83 (Post 16698104)
I think you missed the point I made earlier. Studies have found L/R balance is not consistent. Over the short term (i.e. the duration of an interval) it probably is consistent so it would be useful for maintain a steady effort during an interval.

Depends on the type of interval you're doing. If you're doing high-intensity interval training (like, true Tabatas, which almost no one does because they hurt so much (most people who do "Tabatas" actually do modified Tabatas)) then they could very definitely show inconsistent results -- or maybe not. The research seems to show that as you get toward more FTP-like training over longer intervals bilateral asymmetry becomes more consistent because you're running up against an aerobic limitation rather than an anaerobic neuromuscular limitation. Of course, the research also shows that bilateral asymmetry can worsen as you fatigue. So the bottom line is that if all your training is sort of close to FTP (bilateral asymmetry can get worse if you're going too easy or too hard) and for not too long (bilateral asymmetry can get worse if you're fatigued) and you don't do QA analysis or drag estimation, and your cadence isn't too low or too high (bilateral asymmetry appears to be loosely related to cadence) then you're probably going to be okay with one-sided power meter.

Pro riders do huge training volume so the importance of data quality in any single training session isn't really all that important, and they usually don't use a power meter to pace their races anyway. Most of us only have a limited amount of training time, we can't (mostly) can't afford wind tunnel time, and many of us are trying to learn how to pace properly so, perhaps paradoxically, many of us need a different level of data quality from our devices. I have a buddy who, when he was a college student, used to paint houses as a summer job. He said "professional quality" paint is the lowest quality because it takes a professional to make the paint cover in one coat. Instead of painting houses, I used to work in a butcher shop. I've seen knives in peoples' kitchens much much nicer than the knives professional butchers use. I have another friend who worked as a prep cook in a fancy restaurant. The pots and pans in that restaurant were bent and beat-up.Skill and specificity of purpose can make up for a lot of deficiencies in the tools we use.

Quote:

You just might have a little more trouble measuring changes in performance.
Maybe. Maybe not.

gsa103 04-24-14 09:42 AM

Quote:

Originally Posted by TexMac (Post 16698081)
I would like to see a pro or TDF rider given a choice of Alu & Carbon which bike he/she would use for all stages. Maybe this is our next topic :)

They would all choose carbon. Assuming you had an exactly identical frames, the carbon frame would be ~200g lighter. That extra weight can be used for something like power meters, bar padding, a heavier saddle, etc. Its possible to get an Al frame under weight, its much easier with carbon, that alone will make it more desirable.

The main argument for Al frames is cost. Cost is probably the only thing about the bikes that the pro riders do not care about at all.

achoo 04-24-14 11:33 AM

Quote:

Originally Posted by jsutkeepspining (Post 16697979)
But powertap actually measures your total power, not just your right or left leg. I don't like the idea of variable leg imbalances messing with my data, especially if i'm actually paying money for the powermeter. Also, i don't think knowing your leg balance actually matters in real training. There just isn't much of a use for that type of data barring injuries.

Also, a PowerTap, SRM, or Quarq tells you no more about your left/right power balance than a Stages meter that only measures your left side power.

The only way to know is to measure both left and right power. Or left and total power. Or right and total power.

hhnngg1 04-24-14 11:49 AM

Quote:

Originally Posted by jsutkeepspining (Post 16696120)
you give someone money they will ride what every you want. They are also riding pinerellos which are typically heavier and less aerodynamic than other possible bike sponsors.

Only true to a point - in pro competition in sports, if a product is clearly penalizing you because it's underperforming, it'll get dropped pretty quickly from the pro ranks. Especially in cycling, where equipment choices can make or break.

I still think SRM will probably be better, but I've seen enough user reviews of Stages that it seems to work perfectly well, even for high level athletes.

jsutkeepspining 04-24-14 12:28 PM

Quote:

Originally Posted by achoo (Post 16698814)
Also, a PowerTap, SRM, or Quarq tells you no more about your left/right power balance than a Stages meter that only measures your left side power.

The only way to know is to measure both left and right power. Or left and total power. Or right and total power.

I know. I said that. left/right balance isn't really a useful feature. Knowing your true total power is useful, or at least more useful than just left leg power times 2.

gsa103 04-24-14 01:18 PM

Quote:

Originally Posted by achoo (Post 16698814)
Also, a PowerTap, SRM, or Quarq tells you no more about your left/right power balance than a Stages meter that only measures your left side power.

The only way to know is to measure both left and right power. Or left and total power. Or right and total power.

So the question is can you get a Stages + PowerTap for less than the cost of a Garmin Vector (probably)?

achoo 04-24-14 01:32 PM

Quote:

Originally Posted by gsa103 (Post 16699047)
So the question is can you get a Stages + PowerTap for less than the cost of a Garmin Vector (probably)?

Yeah, but then you need two head units. And some way to calibrate the measured power from the two devices. Because there will be drive train losses that the PowerTap won't measure.

It might be better to attach a Stages crank arm to an SRM or Quarq.

And then you have to combine two data files, and sychronize the individual data points.

It's probably important to also point out that the recording resolution of the head unit(s) might not be good enough to actually get a right/left power split.

Looigi 04-24-14 01:32 PM

Quote:

Originally Posted by jsutkeepspining (Post 16696120)
you give someone money they will ride what every you want. They are also riding pinerellos which are typically heavier and less aerodynamic than other possible bike sponsors.

Not entirely accurate. They won't ride something that significantly impacts their ability to get results, because it's the results that got them where they are and what they're ultimately paid for. Actually, in certain situations, you'll see pros relabeling something that works with the label of a sponsor whose product doesn't work as well for that specific purpose.

So, the Stages PM may not be best but they work well enough and they pay Sky enough for Sky to use them for the purposes we see Sky using them for.

That said, it still wouldn't be my choice. I'd go with a Powertap wheel, or if I felt flush, with Garmin Vector pedals.

TexMac 04-24-14 02:05 PM

Quote:

Originally Posted by canam73 (Post 16698127)
Have you ever read one of DCRainmaker's reviews? This is how he rolls:

http://www.dcrainmaker.com/images/20...erobars-11.jpg

I was reading his reviews the other day and guy has like 3 power meters at once. He did say the iBike power meter was as accurate as the other 3

Campag4life 04-24-14 02:35 PM

Any studies been done to determine the % difference between stages left leg power correlated to other power meters be it crank based or wheel hub?
Aside from correlation, this would statistically shake out typical difference in left and right leg power output. I have to believe most have a dominant leg and this may change actual power up or down by 5% or so. I am pretty such I am right leg dominant and if the stages is on the left leg this would account for some difference.

RChung 04-24-14 02:43 PM

Quote:

Originally Posted by Campag4life (Post 16699251)
Any studies been done to determine the % difference between stages left leg power correlated to other power meters be it crank based or wheel hub?

Depends what you mean by "studies." There have been individuals who have done rides with more than one power meter and then shared the data, but I don't know of any study with large (or even smallish) test populations. Anyway, here's one example from Ray Maker. Since Ray is just one guy, we don't know how your or anyone else's results would differ.

http://www.dcrainmaker.com/images/20...wer_curves.png

Campag4life 04-24-14 02:53 PM

Quote:

Originally Posted by RChung (Post 16699273)
Depends what you mean by "studies." There have been individuals who have done rides with more than one power meter and then shared the data, but I don't know of any study with large (or even smallish) test populations. Anyway, here's one example from Ray Maker. Since Ray is just one guy, we don't know how your or anyone else's results would differ.

http://www.dcrainmaker.com/images/20...wer_curves.png


Thanks. I'm color blind. Can you tell me which power device deviates away from the cluster for first 100 seconds? Can you comment or has there been speculation for this outliar which converges after greater time duration?

Bah Humbug 04-24-14 03:03 PM

Quote:

Originally Posted by achoo (Post 16698814)
Also, a PowerTap, SRM, or Quarq tells you no more about your left/right power balance than a Stages meter that only measures your left side power.

The only way to know is to measure both left and right power. Or left and total power. Or right and total power.

Again, why do you care about individual left/right power as opposed to total?

aggarcia 04-24-14 03:24 PM

The reviews of Stages have been very good. Team Sky would not put anything on their race bikes if it negatively affected performance. I purchased a Stages Ultegra 6700 PM back in Dec. I am not a racer, but a cyclist that likes to use modern technology and tools to improve my performance on the bike. As an IT person, I love the metrics and data available. All the different PM models give you a different power number from each other, does that make them all wrong.

For training purposes, the data must be consistent and reliable. In my several months of Stages use, the data has been very useful. The Stages fit my needs and budget. A good wheelset with a Power Tap G3 starts out of $1500 ad goes up. The test of someone’s happiness with a product is, would you buy it again or something else if doing this over again. I am so impressed with the stages product; I will be buying another one late this summer when I buy a new bike.

RChung 04-24-14 03:25 PM

Quote:

Originally Posted by Campag4life (Post 16699295)
Thanks. I'm color blind. Can you tell me which power device deviates away from the cluster for first 100 seconds? Can you comment or has there been speculation for this outliar which converges after greater time duration?

That's the Stages. For this one ride (a climb), with this one rider (Ray), the PT, Quarq, and Vector all were pretty close while the Stages was farther off. This is a maximal power curve over the average number of seconds on the x-axis, and these were *not* sprints so much as accelerations. For this ride the lines converge at the right side of the plot because you're averaging over a longer period of time so short fluctuations get averaged out. A different rider, on a different type of ride, could have a different pattern of divergence. We know that L/R balance (bilateral asymmetry) varies across individuals, by cadence, by fatigue state, and by power; that is, it's not consistent. That is, on a different ride Ray's balance may have been different -- so if you're doing tests, you'd want to be especially careful with the Stages to do the tests on the same road in possibly the same gear combos each time. OTOH, if all you do is record your TSS, the Stages is probably fine.

It's plots like this that make me think that if you need to do QA analysis, or sprint training, or drag estimation, or if you have been using a different PM for a while for structured training, the Stages probably isn't the right PM for you. However, if all you want to do is ride it's probably okay. I think the Stages can be a good gateway drug before moving on to the hard stuff.

Dunbar 04-24-14 04:08 PM

Quote:

Originally Posted by aggarcia (Post 16699374)
A good wheelset with a Power Tap G3 starts out of $1500 ad goes up.

Good custom built aluminum G3 wheel sets start at $1100-1200. Technically all you need is the rear wheel which goes for $900-1000. But I'll admit most people want their front and rear wheels to match.

hueyhoolihan 04-24-14 04:16 PM

what happens when a power meter user knows EXACTLY how much power they are putting out (if such a thing is possible), but still can't catch the commuter with the flatbar bike in front of them? :lol:

Dunbar 04-24-14 04:19 PM

Quote:

Originally Posted by hueyhoolihan (Post 16699499)
what happens when power meter user knows EXACTLY how much power they are putting out (if such a thing is possible), but still can't catch the commuter with the flatbar bike in front of them? :lol:

This is the potential down side of getting a power meter. It can confirm that you are slow/weak. And I've learned that when it comes to cycling never to judge a book by it's cover.

TrojanHorse 04-24-14 04:24 PM

Quote:

Originally Posted by hueyhoolihan (Post 16699499)
what happens when power meter user knows EXACTLY how much power they are putting out (if such a thing is possible), but still can't catch the commuter with the flatbar bike in front of them? :lol:

And I quote "I'm on a recovery ride"

:lol:

RChung 04-24-14 04:34 PM

Quote:

Originally Posted by hueyhoolihan (Post 16699499)
what happens when power meter user knows EXACTLY how much power they are putting out (if such a thing is possible), but still can't catch the commuter with the flatbar bike in front of them? :lol:

Hmmm. I wouldn't know. I haven't been in that situation since I started using a power meter.

bikepro 04-24-14 04:41 PM

Quote:

Originally Posted by Homebrew01 (Post 16696202)
This.

If I had an IBike, I would always be wondering how accurate it really is.

I bought a used wired PowerTap wheel for $250 instead.

I had a wired PowerTap and they work just fine. The only problem is you have to use a pretty basic head unit. You should be able to find a used ANT+ wireless model pretty cheap on eBay.

Dunbar 04-24-14 04:48 PM

Quote:

Originally Posted by bikepro (Post 16699585)
I had a wired PowerTap and they work just fine. The only problem is you have to use a pretty basic head unit. You should be able to find a used ANT+ wireless model pretty cheap on eBay.

With new G3 hubs going for $700 I wouldn't bother with the older wireless Powertaps at this point. There's a good chance you'll have to send it in for a repair in the near future which costs $350 plus shipping (they upgrade it to G3 internals.) From what I've read the older SL+ tends to leak over time and let moisture in.


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