New Power meter(s) depression.

Mar 27, 17 6:52

Post #1 of 62 Views: 5906

Last year I wrote on this forum about a new Power2Max meter that was reading low, or so it seemed. My times on my TT bike were up, but my power was down. I was avg. 36-37kmh on training rides with power 15-20watts lower than the year before.

The biggest difference between 2016 and 2017 was the switch from my trusty powertap sl+ to a Power2max for the TT bike. I figured the Power2Max was reading low as al of my timing data on long climbs etc. on the road bike with the powertap sl+ seemed to suggest those numbers were accurate, especially compared to others I rode with or others on Strava.

Enter a new bike and a new powertap GS hub. Well, it looks like the Power2max was the more accurate meter, or at least the GS hub reflects numbers closer to the Power2max.

But now I am depressed and grieving the loss of 20-25 watts. I had a 1hour best power of 286 last year, and I had a major goal of reaching 300watts this year. But now it looks like my true FTP was somewhere around 260-70 and 300 is way to far out of reach.

I understand these numbers do not actually matter, overall I was the fastest I have ever been on my TT bike last year, and will hopefully be faster this year. So this post is kind of tongue in cheek. But man, 300 watt FTP was going to feel nice...

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 6:59

Post #2 of 62 Views: 5877

I feel your pain. I am recently in nearly the same situation when I updated the firmware on my Kickr. My true FTP dropped about 15 watts (276-> 261). I too had a goal of 300 watts and this will likely be out of reach now for 2017.

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 7:24

Post #3 of 62 Views: 5810

I have a friend in a similar situation. His older PT shows him 15-20w ahead of my G3. I outweigh him by about 15lbs when I'm in shape. He can only drop me on the steepest of hills. I drop him on the flats. Yep, his PM is off.

Congrats on getting faster. All the other numbers are just bench-racing.

Re: New Power meter(s) depression. [holograham] [ In reply to ]

Mar 27, 17 8:10

Post #4 of 62 Views: 5733

holograham wrote:

I feel your pain. I am recently in nearly the same situation when I updated the firmware on my Kickr. My true FTP dropped about 15 watts (276-> 261). I too had a goal of 300 watts and this will likely be out of reach now for 2017.

Lol, same here! Updated my kickr firmware for 2017 and my ftp is lower. :(

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 8:16

Post #5 of 62 Views: 5706

you cant mourn the loss of something you never really had, can you? :)

"as long as it is consistent".............meme

edit: imagine how i felt when i quickly learned to include zeros in AP :0

Last edited by: jeffp: Mar 27, 17 8:17

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 8:23

Post #6 of 62 Views: 5675

Triagain3 wrote:

Last year I wrote on this forum about a new Power2Max meter that was reading low, or so it seemed. My times on my TT bike were up, but my power was down. I was avg. 36-37kmh on training rides with power 15-20watts lower than the year before.

The biggest difference between 2016 and 2017 was the switch from my trusty powertap sl+ to a Power2max for the TT bike. I figured the Power2Max was reading low as al of my timing data on long climbs etc. on the road bike with the powertap sl+ seemed to suggest those numbers were accurate, especially compared to others I rode with or others on Strava.

Enter a new bike and a new powertap GS hub. Well, it looks like the Power2max was the more accurate meter, or at least the GS hub reflects numbers closer to the Power2max.

But now I am depressed and grieving the loss of 20-25 watts. I had a 1hour best power of 286 last year, and I had a major goal of reaching 300watts this year. But now it looks like my true FTP was somewhere around 260-70 and 300 is way to far out of reach.

I understand these numbers do not actually matter, overall I was the fastest I have ever been on my TT bike last year, and will hopefully be faster this year. So this post is kind of tongue in cheek. But man, 300 watt FTP was going to feel nice...

You know it's possible to statically check which PT is reading correctly, right?

I'm not familiar enough with P2max to know if it allows static checks...

There's no reason you should have not known earlier. Just sayin'...

http://bikeblather.blogspot.com/

Re: New Power meter(s) depression. [Tom A.] [ In reply to ]

Mar 27, 17 8:25

Post #7 of 62 Views: 5670

that's for the paranoid types :)

fyi....i dropped my hanging weight on my tile floor. that sucked

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 8:26

Post #8 of 62 Views: 5662

My first powertap hub 7 years ago was my first endeavor into power based training.

I worked my ass off, and my FTP was huge. 370 watts.

But then i went to my first olympic race, hit my numbers, and based on bestbikesplit.com, I should of been the top cyclist in the event (of course i wasnt)

Long story short, my next power meter was a quarq. Able to calibrate with their app and hanging weights

FTP went from 370 down to 285. Bestbikesplit.com started predicting my races within 10 seconds to the quarq power.

Powertap hub remains consistently 85 watts high when i ride my road bike. Still usable, i just adjust my numbers accordingly.

But a real shock to the system when that happened.

How was i supposed to know? nothing to compare against.... until the quarq.

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 8:27

Post #9 of 62 Views: 5655

And this is why precision AND accuracy matter. There's this "consistency" mantra that a lot of folks are on and mostly because they don't want to spend money on a real power meter and just want a silly stages unit or a single sided pm.

Use this as motivation to keep improving. You'll get there.

Re: New Power meter(s) depression. [randomtriguy] [ In reply to ]

Mar 27, 17 9:07

Post #10 of 62 Views: 5549

randomtriguy wrote:

My first powertap hub 7 years ago was my first endeavor into power based training.

I worked my ass off, and my FTP was huge. 370 watts.

But then i went to my first olympic race, hit my numbers, and based on bestbikesplit.com, I should of been the top cyclist in the event (of course i wasnt)

Long story short, my next power meter was a quarq. Able to calibrate with their app and hanging weights

FTP went from 370 down to 285. Bestbikesplit.com started predicting my races within 10 seconds to the quarq power.

Powertap hub remains consistently 85 watts high when i ride my road bike. Still usable, i just adjust my numbers accordingly.

But a real shock to the system when that happened.

How was i supposed to know? nothing to compare against.... until the quarq.

Incorrect. You have always been able to statically check a PT hub. Look up "Powertap stomp test".

C'mon people...NO powermeter should be put into service without at least a static torque check...and if the PM doesn't allow for that, you might want to reconsider the use of it.

http://bikeblather.blogspot.com/

Re: New Power meter(s) depression. [Tom A.] [ In reply to ]

Mar 27, 17 9:17

Post #11 of 62 Views: 5510

Yeah - I wasnt aware of it at the time -- Quarq introduced me to Qalvin and the process for calibrating and adjusting slope.

As someone new to power meters in 2010, I had no idea anything needed to be done -- powertap hub was often plugged as a "it just works" device

Looking back though -- absolutely

Re: New Power meter(s) depression. [Tom A.] [ In reply to ]

Mar 27, 17 9:28

Post #12 of 62 Views: 5461

Is there a way to calibrate a P1 Pedal to confirm accuracy?

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 9:42

Post #13 of 62 Views: 5421

Power number obsession is huge on this site.

300 watts is totally unimportant. Instead, what IS important is your power to weight ratio. For example, watts per kg body weight. (Actually watts per unit of drag is more important, but watts/kilo is a very good substitute.)

If you like to chase numbers, create a useful goal like, say, 4.5 watts per kilo of bodyweight ... or something like that appropriate for your body size.

And congrats on doing well in races, because I think that is what actually matters ...

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
--

Last edited by: DarkSpeedWorks: Mar 28, 17 8:31

Re: New Power meter(s) depression. [DarkSpeedWorks] [ In reply to ]

Mar 27, 17 9:47

Post #14 of 62 Views: 5403

DarkSpeedWorks wrote:

Power number obsession is huge on this site.

300 watts is totally unimportant. Instead, what IS important is your power to weight ratio. For example, watts per kg body weight. (Actually watts per unit of drag is more important, but watts/kilo is a very good substitute.)

If you like to chase numbers, create a useful goal like, say, 4.5 watts per kilo of bodyweight ... or something like that appropriate for your bodysize.

And congrats on doing well in races !
Because I think that is what actually matters ...

That is a good metric for pure climbing but not at all when we're talking flatter roads including those with rollers. I know many people with better W/kg than myself which I could easily drop on the flats or even short, steep hills because my absolute power is higher.

Re: New Power meter(s) depression. [Benv] [ In reply to ]

Mar 27, 17 9:51

Post #15 of 62 Views: 5390

Benv wrote:

That is a good metric for pure climbing but not at all when we're talking flatter roads including those with rollers. I know many people with better W/kg than myself which I could easily drop on the flats or even short, steep hills because my absolute power is higher.

Not sure how big you are, but I would wager a guess that most of the other people who have better watts/kg but who you can drop are also not as well set up aerodynamically (body and bike) as you are.

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
--

Re: New Power meter(s) depression. [holograham] [ In reply to ]

Mar 27, 17 10:23

Post #16 of 62 Views: 5317

holograham wrote:

Is there a way to calibrate a P1 Pedal to confirm accuracy?

I don't know...but it would be something to look into before considering them...

http://bikeblather.blogspot.com/

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 10:34

Post #17 of 62 Views: 5274

Ah yes. Why is it that recalibrating a power meter ALWAYS leads to lower numbers? :D

Re: New Power meter(s) depression. [SBRcoffee] [ In reply to ]

Mar 27, 17 10:50

Post #18 of 62 Views: 5240

SBRcoffee wrote:

holograham wrote:

I feel your pain. I am recently in nearly the same situation when I updated the firmware on my Kickr. My true FTP dropped about 15 watts (276-> 261). I too had a goal of 300 watts and this will likely be out of reach now for 2017.

Lol, same here! Updated my kickr firmware for 2017 and my ftp is lower. :(

I love having a proper power meter on my bike.

But these first few months with it trying to close the kickr to power meter FTP gap have been brutal.. really brutal.

Re: New Power meter(s) depression. [DarkSpeedWorks] [ In reply to ]

Mar 27, 17 10:55

Post #19 of 62 Views: 5210

The number of watts is still important since that is one of two inputs for the power to weight ratio...

https://twitter.com/mungub

Re: New Power meter(s) depression. [SteveM] [ In reply to ]

Mar 27, 17 10:55

Post #20 of 62 Views: 5207

Glad I have P1 pedals; I can take my whatever number from one bike to the next one and they will be exactly the same.

The entire event (IM) is like "death by 1000 cuts" and the best race is minimizing all those cuts and losing less blood than the other guy. - Dev

Re: New Power meter(s) depression. [LuisDF] [ In reply to ]

Mar 27, 17 11:15

Post #21 of 62 Views: 5159

LuisDF wrote:

Glad I have P1 pedals; I can take my whatever number from one bike to the next one and they will be exactly the same.

I've read enough bad things about those to keep me from ever buying.

The kickr is for training, not racing. As long as it is consistent. If I want a PM for racing, it's P2M.

Re: New Power meter(s) depression. [SBRcoffee] [ In reply to ]

Mar 27, 17 11:32

Post #22 of 62 Views: 5118

SBRcoffee wrote:

As long as it is consistent.

You are the problem.

Re: New Power meter(s) depression. [stevej] [ In reply to ]

Mar 27, 17 13:08

Post #23 of 62 Views: 4920

stevej wrote:

this is why precision AND accuracy matter.

And the ability to at least check the calibration yourself.

Re: New Power meter(s) depression. [Tom A.] [ In reply to ]

Mar 27, 17 13:15

Post #24 of 62 Views: 4891

Tom A. wrote:

"Powertap stomp test".

Man, that's a blast from the past (1999, to be exact).

Re: New Power meter(s) depression. [Benv] [ In reply to ]

Mar 27, 17 13:18

Post #25 of 62 Views: 4882

Benv wrote:

That is a good metric for pure climbing but not at all when we're talking flatter roads

This misconception seems just as common as the "as long as it's consistent" fallacy.

Re: New Power meter(s) depression. [mungub50] [ In reply to ]

Mar 27, 17 13:24

Post #26 of 62 Views: 3891

mungub50 wrote:

The number of watts is still important since that is one of two inputs for the power to weight ratio...

Sure, but if racing well is your goal, the super strong 180 lb guy who puts out a lot more watts than the 140 lb guy can still get his butt kicked on the flats, hills, or whereever by the 140 lb guy.

Relative power is way more important than absolute power.
And the king of all numbers for tri biking is the power-to-drag ratio.

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
--

Re: New Power meter(s) depression. [Andrew Coggan] [ In reply to ]

Mar 27, 17 13:32

Post #27 of 62 Views: 3883

Andrew Coggan wrote:

Benv wrote:

That is a good metric for pure climbing but not at all when we're talking flatter roads

This misconception seems just as common as the "as long as it's consistent" fallacy.

Can you explain, in detail, this fallacy?

Re: New Power meter(s) depression. [DarkSpeedWorks] [ In reply to ]

Mar 27, 17 13:56

Post #28 of 62 Views: 3859

Why is accuracy important? Important to predict how well you do compared to others? Or important to base of your training plan?

I always thought that consistency is all you need to train 'well'. So excuse my ignorance, but I'm trying to understand.

Last edited by: IvarAlmere: Mar 27, 17 14:03

Re: New Power meter(s) depression. [SBRcoffee] [ In reply to ]

Mar 27, 17 14:27

Post #29 of 62 Views: 3828

I got them a month after they came out and they always within a few watts of CT and quarqs (I sold the quarqs long time ago tho)

The entire event (IM) is like "death by 1000 cuts" and the best race is minimizing all those cuts and losing less blood than the other guy. - Dev

Re: New Power meter(s) depression. [DarkSpeedWorks] [ In reply to ]

Mar 27, 17 14:30

Post #30 of 62 Views: 3820

DarkSpeedWorks wrote:

mungub50 wrote:

The number of watts is still important since that is one of two inputs for the power to weight ratio...

Sure, but if racing well is your goal, the super strong 180 lb guy who puts out a lot more watts than the 140 lb guy can still get his butt kicked on the flats, hills, or whereever by the 140 lb guy.

Relative power is way more important than absolute power.
And the king of all numbers for tri biking is the power-to-drag ratio.

This

In a 10 miler u might make the skinnier guy hurt but most races are a lot longer than 10 miles and usually big guys are great for drafting after u cover their first big acceleration.

The entire event (IM) is like "death by 1000 cuts" and the best race is minimizing all those cuts and losing less blood than the other guy. - Dev

Re: New Power meter(s) depression. [SBRcoffee] [ In reply to ]

Mar 27, 17 14:33

Post #31 of 62 Views: 3815

I have both p1 and power2max ng and power2max reads 4w higher than p1. Before I had a power2max classic and that one was about 2w plus/minus don't remember which.

SBRcoffee wrote:

LuisDF wrote:

Glad I have P1 pedals; I can take my whatever number from one bike to the next one and they will be exactly the same.

I've read enough bad things about those to keep me from ever buying.

The kickr is for training, not racing. As long as it is consistent. If I want a PM for racing, it's P2M.

Re: New Power meter(s) depression. [sp1ke] [ In reply to ]

Mar 27, 17 14:36

Post #32 of 62 Views: 3806

sp1ke wrote:

I have both p1 and power2max ng and power2max reads 4w higher than p1. Before I had a power2max classic and that one was about 2w plus/minus don't remember which.

SBRcoffee wrote:

LuisDF wrote:

Glad I have P1 pedals; I can take my whatever number from one bike to the next one and they will be exactly the same.

I've read enough bad things about those to keep me from ever buying.

The kickr is for training, not racing. As long as it is consistent. If I want a PM for racing, it's P2M.

With regards to the P1's, I don't doubt their accuracy, I doubt their overall reliability.

Re: New Power meter(s) depression. [SBRcoffee] [ In reply to ]

Mar 27, 17 16:22

Post #33 of 62 Views: 3753

Me too :-)

SBRcoffee wrote:

sp1ke wrote:

I have both p1 and power2max ng and power2max reads 4w higher than p1. Before I had a power2max classic and that one was about 2w plus/minus don't remember which.

SBRcoffee wrote:

LuisDF wrote:

Glad I have P1 pedals; I can take my whatever number from one bike to the next one and they will be exactly the same.

I've read enough bad things about those to keep me from ever buying.

The kickr is for training, not racing. As long as it is consistent. If I want a PM for racing, it's P2M.

With regards to the P1's, I don't doubt their accuracy, I doubt their overall reliability.

Re: New Power meter(s) depression. [jeffp] [ In reply to ]

Mar 27, 17 16:41

Post #34 of 62 Views: 3739

jeffp wrote:

that's for the paranoid types :)

fyi....i dropped my hanging weight on my tile floor. that sucked

Better the tile than your toe, eh?

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 16:52

Post #35 of 62 Views: 3735

My power2max was reading 20-25 watts low as well. Low compared to other meters. The p2m was consistent though. I decided to buy the new NG and see how it goes and I can use it in all three of my bikes (BB86)

Re: New Power meter(s) depression. [BrianB] [ In reply to ]

Mar 27, 17 17:22

Post #36 of 62 Views: 3725

I did not patch it for a long time, until my labs starting to dig it larger :)

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 27, 17 18:42

Post #37 of 62 Views: 3686

Triagain3 wrote:

Andrew Coggan wrote:

Benv wrote:

That is a good metric for pure climbing but not at all when we're talking flatter roads

This misconception seems just as common as the "as long as it's consistent" fallacy.

Can you explain, in detail, this fallacy?

The fallacy is that body size (as indicated by mass) does not influence the energy cost of cycling on level terrain.

The reality is that it does, by impacting 1) aerodynamic drag, 2) rolling resistance, and 3) inertia (when speed is not constant).

Re: New Power meter(s) depression. [Tom A.] [ In reply to ]

Mar 27, 17 19:18

Post #38 of 62 Views: 3649

Tom A. wrote:

C'mon people...NO powermeter should be put into service without at least a static torque check...and if the PM doesn't allow for that, you might want to reconsider the use of it.

People buy PMs based on features, and that's a mistake. Being able to check the accuracy of your PM is like having the 9 key on a calculator. It's not a feature, it's a key.

Re: New Power meter(s) depression. [RChung] [ In reply to ]

Mar 27, 17 19:38

Post #39 of 62 Views: 3634

RChung wrote:

Tom A. wrote:

C'mon people...NO powermeter should be put into service without at least a static torque check...and if the PM doesn't allow for that, you might want to reconsider the use of it.

People buy PMs based on features, and that's a mistake. Being able to check the accuracy of your PM is like having the 9 key on a calculator. It's not a feature, it's a key.

Why is there an assumption that a static torque check will verify every calibration?

Has anyone ever put a Quarq or SRM on a dyno to see if their static calibration is in fact correct?

I have dealt with rotary torque cells that cannot be calibrated by hanging weights alone.

Re: New Power meter(s) depression. [mtbr] [ In reply to ]

Mar 27, 17 21:57

Post #40 of 62 Views: 3589

mtbr wrote:

Why is there an assumption that a static torque check will verify every calibration?

Has anyone ever put a Quarq or SRM on a dyno to see if their static calibration is in fact correct?

I have dealt with rotary torque cells that cannot be calibrated by hanging weights alone.

Hmmm. Why are you assuming that we assume that a static torque check verifies every calibration? A correct static reading of torque is a necessary but not sufficient condition for accuracy.

Re: New Power meter(s) depression. [Triagain3] [ In reply to ]

Mar 28, 17 1:08

Post #41 of 62 Views: 3544

Usually I keep track of 2 important aspects in cycling:
1) 20mins all out test (indoor + outdoor)
2) 20mins all out test on a hill of 5-7% grade

Looking at both results, I can understand very well where I am at, every season.
for the first test, i pay attention only at the average power.
for the second test, I pay attention to the VAM which correlate somehow the average power to my body weight.
you can't neglect your body weight in assessing your fitness level.

regarding powermeters accuracy/precision:
I have a Quarq and my wife has P2max
we went to test our power in a lab where we could calibrate our bikes (powermeters) to a common smart trainer.
Her P2max was about 25W lower for the whole curve 100-400W, linearly, compared to the common trainer.

We were very surprised and so we wanted to replicate it outside just roughly. we went side to side on a hill, she is 1kg more than me (let's say identical), same Cervelo S3, both 2 waterbottles, and we climbed at the same speed. 20-25W difference confirmed.

just to let you know you should never rely on web calculations (on your final bike split) or comparison between 2 cyclist with different powermeters (even the same model can give you different statistics!).

Re: New Power meter(s) depression. [RChung] [ In reply to ]

Mar 28, 17 3:08

Post #42 of 62 Views: 3493

RChung wrote:

mtbr wrote:

Why is there an assumption that a static torque check will verify every calibration?

Has anyone ever put a Quarq or SRM on a dyno to see if their static calibration is in fact correct?

I have dealt with rotary torque cells that cannot be calibrated by hanging weights alone.

Hmmm. Why are you assuming that we assume that a static torque check verifies every calibration? A correct static reading of torque is a necessary but not sufficient condition for accuracy.

I'm not trolling, I'm genuinely curious. I understand your thinking now.

Re: New Power meter(s) depression. [mtbr] [ In reply to ]

Mar 28, 17 4:10

Post #43 of 62 Views: 3454

mtbr wrote:

Has anyone ever put a Quarq or SRM on a dyno to see if their static calibration is in fact correct?

Yes. In fact, I am even last author on a peer-reviewed paper describing the results of one of many such comparisons that I have made: https://www.academia.edu/...mech_1998_14_276-291

There are other peer-reviewed papers performing similar tests.

Although static testing won't reveal all measurement errors (witness the torque spikes generated by the Quarq described here: http://www.trainingandracingwithapowermeter.com/...r-type-from.html?m=1), it is definitely the first place to start.

(Note that back in 1999 I actually relied on a dynamic test of my original PowerTap hub, describing/attempting a static check only as a backup: https://groups.google.com/...mndbKeg/fYmeQBa4ksUJ)

Last edited by: Andrew Coggan: Mar 28, 17 4:16

Re: New Power meter(s) depression. [Andrew Coggan] [ In reply to ]

Mar 28, 17 4:27

Post #44 of 62 Views: 3445

Thank you very much :)

Re: New Power meter(s) depression. [SBRcoffee] [ In reply to ]

Mar 28, 17 5:05

Post #45 of 62 Views: 3419

SBRcoffee wrote:

sp1ke wrote:

I have both p1 and power2max ng and power2max reads 4w higher than p1. Before I had a power2max classic and that one was about 2w plus/minus don't remember which.

SBRcoffee wrote:

LuisDF wrote:

Glad I have P1 pedals; I can take my whatever number from one bike to the next one and they will be exactly the same.

I've read enough bad things about those to keep me from ever buying.

The kickr is for training, not racing. As long as it is consistent. If I want a PM for racing, it's P2M.

With regards to the P1's, I don't doubt their accuracy, I doubt their overall reliability.

almost 2yrs and going strong; I even scraped the bottom of the pedals doing crits and it wasn't a problem at all.

The entire event (IM) is like "death by 1000 cuts" and the best race is minimizing all those cuts and losing less blood than the other guy. - Dev

Re: New Power meter(s) depression. [mtbr] [ In reply to ]

Mar 28, 17 5:58

Post #46 of 62 Views: 3380

mtbr wrote:

RChung wrote:

Tom A. wrote:

C'mon people...NO powermeter should be put into service without at least a static torque check...and if the PM doesn't allow for that, you might want to reconsider the use of it.

People buy PMs based on features, and that's a mistake. Being able to check the accuracy of your PM is like having the 9 key on a calculator. It's not a feature, it's a key.

Why is there an assumption that a static torque check will verify every calibration?

Has anyone ever put a Quarq or SRM on a dyno to see if their static calibration is in fact correct?

I have dealt with rotary torque cells that cannot be calibrated by hanging weights alone.

The AIS has published a number of studies comparing the outputs of SRMs, PTs, etc. with dynamic calibrations, which I'm sure you can find in a web search.

Also, take a look at a typical crank torque plot, and you'll easily see that the vast majority of the torque is applied through a fairly narrow range, so checking the torque output in that same area is going to result in a pretty good idea of how well it will be able to measure the power output of a human cyclist. Once you have that, measuring average crank rotational velocity is fairly trivial, and those are the 2 inputs to calculate power.

http://bikeblather.blogspot.com/

Re: New Power meter(s) depression. [RChung] [ In reply to ]

Mar 28, 17 6:02

Post #47 of 62 Views: 3370

RChung wrote:

mtbr wrote:

Why is there an assumption that a static torque check will verify every calibration?

Has anyone ever put a Quarq or SRM on a dyno to see if their static calibration is in fact correct?

I have dealt with rotary torque cells that cannot be calibrated by hanging weights alone.

Hmmm. Why are you assuming that we assume that a static torque check verifies every calibration? A correct static reading of torque is a necessary but not sufficient condition for accuracy.

Exactly...to get my Polar PMs reading properly, all I needed was an accurate chain mass measurement (and a "good" setup) ;-)

http://bikeblather.blogspot.com/

Re: New Power meter(s) depression. [Tom A.] [ In reply to ]

Mar 28, 17 6:05

Post #48 of 62 Views: 3363

Thank you

Re: New Power meter(s) depression. [Andrew Coggan] [ In reply to ]

Mar 28, 17 6:07

Post #49 of 62 Views: 3360

Andrew Coggan wrote:

Triagain3 wrote:

Andrew Coggan wrote:

Benv wrote:

That is a good metric for pure climbing but not at all when we're talking flatter roads

This misconception seems just as common as the "as long as it's consistent" fallacy.

Can you explain, in detail, this fallacy?

The fallacy is that body size (as indicated by mass) does not influence the energy cost of cycling on level terrain.

The reality is that it does, by impacting 1) aerodynamic drag, 2) rolling resistance, and 3) inertia (when speed is not constant).

I have no disagreement with your statement above, and I believe I understand your point properly.

However, I thought what people were saying when they said "as long as it's consistent" was the power meter needed to give the same reading (even if off by a few points from the true number) consistently in order to be useful as a tool for training. I never read this statement to imply that body size did not matter.

Would you agree or disagree that a consistent powermeter was the most important factor when using it as a training tool for the average cyclist? Or does it also have to be accurate?

Re: New Power meter(s) depression. [Tom A.] [ In reply to ]

Mar 28, 17 6:56

Post #50 of 62 Views: 3320

Tom A. wrote:

Once you have that, measuring average crank rotational velocity is fairly trivial, and those are the 2 inputs to calculate power.

Relatively trivial but not entirely. We both know of certain PMs whose cadence measurements can be noisy in certain situations. Sometimes I think manufacturers were too fast in moving away from magnets and reed switches.

Re: New Power meter(s) depression. [Plissken74] [ In reply to ]

Mar 28, 17 7:11

Post #51 of 62 Views: 1684

Plissken74 wrote:

I have a Quarq and my wife has P2max [..] 20-25W difference confirmed.

That's interesting. Have you done a static torque check with the same weights?

Re: New Power meter(s) depression. [RChung] [ In reply to ]

Mar 28, 17 8:10

Post #52 of 62 Views: 1643

RChung wrote:

Plissken74 wrote:

I have a Quarq and my wife has P2max [..] 20-25W difference confirmed.

That's interesting. Have you done a static torque check with the same weights?

Never done it. Do you think it would be beneficial also on these 2 models?

Re: New Power meter(s) depression. [Plissken74] [ In reply to ]

Mar 28, 17 9:19

Post #53 of 62 Views: 1622

It's possible and, if you already have the weights and a stable base to mount the bikes onto, it can be easier. Maybe both the smart trainer and the Quarq are off, and the P2M is right. Hanging known weights off the pedal will nail that down.

But it's good you did that hill climb.

Once you know that your PMs are right, you can use them for measuring drag.

Re: New Power meter(s) depression. [RChung] [ In reply to ]

Mar 28, 17 12:45

Post #54 of 62 Views: 1566

RChung wrote:

It's possible and, if you already have the weights and a stable base to mount the bikes onto, it can be easier. Maybe both the smart trainer and the Quarq are off, and the P2M is right. Hanging known weights off the pedal will nail that down.

But it's good you did that hill climb.

Once you know that your PMs are right, you can use them for measuring drag.

or keeping an accurate record of one's decline...

http://www.cyclecoach.com
http://www.aerocoach.com.au

Re: New Power meter(s) depression. [AlexS] [ In reply to ]

Mar 28, 17 12:47

Post #55 of 62 Views: 1562

AlexS wrote:

RChung wrote:

Once you know that your PMs are right, you can use them for measuring drag.

or keeping an accurate record of one's decline...

That too.

Re: New Power meter(s) depression. [AlexS] [ In reply to ]

Mar 28, 17 17:27

Post #56 of 62 Views: 1503

AlexS wrote:

or keeping an accurate record of one's decline...

Does it need to be an accurate record or can it just be consistent?

Re: New Power meter(s) depression. [jaretj] [ In reply to ]

Mar 28, 17 17:32

Post #57 of 62 Views: 1498

jaretj wrote:

AlexS wrote:

or keeping an accurate record of one's decline...

Does it need to be an accurate record or can it just be consistent?

Given human life span is typically longer than power meter life span, the power meters need to be accurate.

http://www.cyclecoach.com
http://www.aerocoach.com.au

Re: New Power meter(s) depression. [RChung] [ In reply to ]

Mar 28, 17 22:33

Post #58 of 62 Views: 1453

RChung wrote:

Tom A. wrote:

Once you have that, measuring average crank rotational velocity is fairly trivial, and those are the 2 inputs to calculate power.

Relatively trivial but not entirely. We both know of certain PMs whose cadence measurements can be noisy in certain situations. Sometimes I think manufacturers were too fast in moving away from magnets and reed switches.

it's a shame that taking a simple measurement once a revolution got replaced by something more complex which is then billed as a 'feature' -- yet in the real world provides less accuracy.

so many Quarq users got excited when they were finally free to ditch their (perfectly functional) magnets.

i heard a few stories of people who supposedly destroyed a derailleur when their magnet got sucked onto their chain. in the better part of a decade of riding with power on road bikes, mountain bikes and cross bikes, i've never seen this happen.

Re: New Power meter(s) depression. [tetonrider] [ In reply to ]

Mar 29, 17 5:05

Post #59 of 62 Views: 1392

tetonrider wrote:

RChung wrote:

Tom A. wrote:

Once you have that, measuring average crank rotational velocity is fairly trivial, and those are the 2 inputs to calculate power.

Relatively trivial but not entirely. We both know of certain PMs whose cadence measurements can be noisy in certain situations. Sometimes I think manufacturers were too fast in moving away from magnets and reed switches.

it's a shame that taking a simple measurement once a revolution got replaced by something more complex which is then billed as a 'feature' -- yet in the real world provides less accuracy.

so many Quarq users got excited when they were finally free to ditch their (perfectly functional) magnets.

i heard a few stories of people who supposedly destroyed a derailleur when their magnet got sucked onto their chain. in the better part of a decade of riding with power on road bikes, mountain bikes and cross bikes, i've never seen this happen.

It happened to someone I was riding with. No damage to the bike however.

I agree though. It's too bad the technological cure for poorly installed magnets was in reality more trade-off than cure

Mark E

Re: New Power meter(s) depression. [mark.ewers] [ In reply to ]

Mar 29, 17 13:25

Post #60 of 62 Views: 1335

I've had two magnets dislodge from their holding bracket and get stuck in between two of the rear cogs. No damage as they are small and just made the chain skip a bit in that gear.

The irony is they are the Quarq magnets (while I use SRMs I had some spare Quarq magnets from a time when I used to service faulty Quarqs here in Australia, before the days of SRAM), which while the design of the BB mount magnet bracket is nice and easy to fit, the glue securing the magnet onto the bracket isn't strong enough to survive a knock or being hit by a dropped chain and it could use a better magnet attachment design.

http://www.cyclecoach.com
http://www.aerocoach.com.au

Re: New Power meter(s) depression. [AlexS] [ In reply to ]

Mar 29, 17 16:49

Post #61 of 62 Views: 1298

AlexS wrote:

I've had two magnets dislodge from their holding bracket and get stuck in between two of the rear cogs. No damage as they are small and just made the chain skip a bit in that gear.

The irony is they are the Quarq magnets (while I use SRMs I had some spare Quarq magnets from a time when I used to service faulty Quarqs here in Australia, before the days of SRAM), which while the design of the BB mount magnet bracket is nice and easy to fit, the glue securing the magnet onto the bracket isn't strong enough to survive a knock or being hit by a dropped chain and it could use a better magnet attachment design.

Same, I lost three quarq magnets. The first used the provided epoxy putty and BB mount. The second used superglue to adhere the magnet to the bb mount. The third was a pre-adhered bb mount from quarq. Finally I used liberal amount of industrial hot melt to secure a magnet to the bb mount. Worked very well.

Re: New Power meter(s) depression. [Pantelones] [ In reply to ]

Mar 29, 17 17:17

Post #62 of 62 Views: 1283

Pantelones wrote:

AlexS wrote:

I've had two magnets dislodge from their holding bracket and get stuck in between two of the rear cogs. No damage as they are small and just made the chain skip a bit in that gear.

The irony is they are the Quarq magnets (while I use SRMs I had some spare Quarq magnets from a time when I used to service faulty Quarqs here in Australia, before the days of SRAM), which while the design of the BB mount magnet bracket is nice and easy to fit, the glue securing the magnet onto the bracket isn't strong enough to survive a knock or being hit by a dropped chain and it could use a better magnet attachment design.

Same, I lost three quarq magnets. The first used the provided epoxy putty and BB mount. The second used superglue to adhere the magnet to the bb mount. The third was a pre-adhered bb mount from quarq. Finally I used liberal amount of industrial hot melt to secure a magnet to the bb mount. Worked very well.

I'm planning on applying some hot glue over the magnet and see what happens if I ever drop a chain again.

http://www.cyclecoach.com
http://www.aerocoach.com.au

Our Partners

transition-DOT-area-AT-slowtwitch-DOT-com

Advertise with us

©1999-2024 Slowtwitch, Inc., and Slowtwitch.com
Reproduction of material from any Slowtwitch.com page
without written permission is strictly prohibited.