The Powermeter Thread

[CoachFergie]

David Bowden is a NZ Engineer and Coach who is doing some excellent commentary on power analysis and aerodynamics (much of which is based on power meter data) and reporting on his blog...

http://speedtheory.co.nz/monitoring-training-effect/

http://speedtheory.co.nz/tour-de-france-observations-from-stages-4-5/

 

[Ripper]

Does anyone read what I write (or write about)?

Mostly, no.

 

[FrankDay]

Mostly, no.

I get that. I guess the real question is why someone would respond to a post that they haven't taken the care to even read, let alone, understand?

 

[Ripper]

I get that. I guess the real question is why someone would respond to a post that they haven't taken the care to even read, let alone, understand?

Depends on which post and who you are talking about.

 

[sciguy]

Looks like the long wait is about over - Garmin Vector

It's taken a good bit longer than expected by some but it finally looks as if the Vector is about to launch.

https://groups.google.com/forum/?fromgroups#!topic/wattage/DKHhRzfvgHw

Now if it's both accurate as well as durable it will be a great tool for many.

Hugh

 

[FrankDay]

It's taken a good bit longer than expected by some but it finally looks as if the Vector is about to launch.

https://groups.google.com/forum/?fromgroups#!topic/wattage/DKHhRzfvgHw

Now if it's both accurate as well as durable it will be a great tool for many.

Hugh

I think it will depend upon what software works with the system. Simply giving R/L power will be a small advance. Giving information about pedaling technique will be a huge advance. Looks like there will be several of these coming to the market about the same time. If they are all reasonably accurate and reliable then software will be the big difference between them.

 

[sciguy]

I think it will depend upon what software works with the system. Simply giving R/L power will be a small advance. Giving information about pedaling technique will be a huge advance.

I agree that right left balance is not particularly important but have a distinct feeling that we will soon find that monitoring pedaling technique isn't either.

Looks like there will be several of these coming to the market about the same time. If they are all reasonably accurate and reliable then software will be the big difference between them.

What would those several be? The Look pedals have seemed to be a real compromise. They are fussy to install, are limited to cranks from 170 to 177.5mm so you can't go with the shorter cranks you love and they only work with Look's proprietary computer head. Brim Brothers cleat based system still seems to be pie in the sky. The Icrank isn't a pedal based system so one's ability to swap between bikes is compromised. You can easily bring the Garmin pedals on vacation via your carry on luggage and have power available on a variety of bikes at your destination.

Looks like a lot of potential up side to the Garmin system to me if they are both accurate as well as durable.

YMMV,

Hugh

 

[CoachFergie]

Just a reminder that the intent of this thread is to discuss the racing and training with a meter that measure's power. Other threads are available to discuss pedalling technique.

 

[CoachFergie]

It's taken a good bit longer than expected by some but it finally looks as if the Vector is about to launch.

https://groups.google.com/forum/?fromgroups#!topic/wattage/DKHhRzfvgHw

Now if it's both accurate as well as durable it will be a great tool for many.

Hugh

I hope it is a more robust system than it looks. Also that it is easier to set up and align than the Polar pedal based system. At least we can assume it will be ANT+ compatible unlike Polar which is based on the WIND system which limits you to only Polar components and has very limited recording capacity.

 

[sciguy]

I hope it is a more robust system than it looks. Also that it is easier to set up and align than the Polar pedal based system.

As I understand things from a reliable source, it's much easier. The pedal itself does not need to be in a specific orientation as it is able to find its orientation.

At least we can assume it will be ANT+ compatible unlike Polar which is based on the WIND system which limits you to only Polar components and has very limited recording capacity.

Yes it is ANT+ based and therefore should be able to be used with a wide assortment of head units with more coming on a near monthly basis.

The sending pod is actually more protected than you might think from the picture. I could see it being harmed in a pile up of bikes but you'd need to work pretty hard to stuff it up otherwise.

At the very least I think it has the potential to fill a niche in the power meter market that has yet to be well filled. If it's accurate and robust it will be a competitive force with the heft of Garmin behind it.

YMMV,

Hugh

 

[FrankDay]

I hope it is a more robust system than it looks. Also that it is easier to set up and align than the Polar pedal based system. At least we can assume it will be ANT+ compatible unlike Polar which is based on the WIND system which limits you to only Polar components and has very limited recording capacity.

My question has to do with how it compensates for different crank lengths. This will be a big deal for those trying to do crank length experimenting if there is not a good compensation.

 

[sciguy]

My question has to do with how it compensates for different crank lengths. This will be a big deal for those trying to do crank length experimenting if there is not a good compensation.

Frank,

The math needed is incredibly simple. What's more surprising to me is that Look didn't bother to set their units up to accommodate a wider range of cranks lengths.

Hugh

 

[FrankDay]

Frank,

The math needed is incredibly simple. What's more surprising to me is that Look didn't bother to set their units up to accommodate a wider range of cranks lengths.

Hugh

The math is incredibly simple but, me thinks, incorporating it into the software isn't quite so simple. For instance, somehow either the Garmin pedals (or the iCranks, or any other crank/pedal/shoe) based system has to know what the crank length is to calculate the proper power. In general the rider doesn't communicate with these units and the pick-ups do not have an input for crank length. How many users will input the data even if there is a way? This was an issue with the iCranks I noticed in that they were calibrated for 172.5mm. Any other crank length resulted in an off-set (compared to the velotron) and the degree of offset varied with the variance. When I was using a Garmin headset on the road and 145mm iCranks I knew that the power I was generating was really about 20% greater than the power I was seeing displayed based upon my testing. It would be a more difficult problem if the rider was riding two different crank lengths because of a leg length discrepancy or injury.

 

[sciguy]

The math is incredibly simple but, me thinks, incorporating it into the software isn't quite so simple. For instance, somehow either the Garmin pedals (or the iCranks, or any other crank/pedal/shoe) based system has to know what the crank length is to calculate the proper power. In general the rider doesn't communicate with these units and the pick-ups do not have an input for crank length. How many users will input the data even if there is a way? This was an issue with the iCranks I noticed in that they were calibrated for 172.5mm. Any other crank length resulted in an off-set (compared to the velotron) and the degree of offset varied with the variance. When I was using a Garmin headset on the road and 145mm iCranks I knew that the power I was generating was really about 20% greater than the power I was seeing displayed based upon my testing. It would be a more difficult problem if the rider was riding two different crank lengths because of a leg length discrepancy or injury.

I'd have to expect that Garmin has already reworked their firmware for the Edge 500 and other more recent head units so that this will just be an easy update once the Vector units are available for sale.

How many users will input the data even if there is a way?

If it's as simple as all the other inputs to a Garmin 500, I'd guess 95% of the people bothering to buy these would do it and the other 5% would get their 8 year old grand child to do it for them. Have you got grand children Frank?

YMMV,

Hugh

 

[FrankDay]

I'd have to expect that Garmin has already reworked their firmware for the Edge 500 and other more recent head units so that this this will just be an easy update once the Vector units are available for sale.

I have an edge 500 and while it sees two power meters (when present) it does not have any inputs to accommodate different calibration for crank length. I would be surprised if they included that right out of the barn.

If it's as simple as all the other inputs to a Garmin 500, I'd guess 95% of the people bothering to buy these would do it and the other 5% would get their 8 year old grand child to do it for them. Have you got grand children Frank?

YMMV,

Hugh

We will see. My guess is this will be the biggest source of inaccuracy with these products.

 

[CoachFergie]

Mountain out of a molehill. Garmin have responded very quickly to rider input and seeing it's their product will have no issues adding crank length to the head unit inputs.

That's good news Hugh, that it is more robust than it looks. Any piece of equipment can't claim to be fully crash proof unless you want a 15kg race bike.

 

[sciguy]

When I was using a Garmin headset on the road and 145mm iCranks I knew that the power I was generating was really about 20% greater than the power I was seeing displayed based upon my testing. /QUOTE]

Just for clarification, did you actually run 145mm Icranks on the Velotron while also reading the power output as displayed on the Garmin head unit to come up with this 20% value?

Are you running a Powertap rear wheel in tandem with the Icranks so you can compare to something that's actually validated on the road? Some of the recently introduced power meters have looked pretty good when used on a trainer but not nearly as good on the road.........thinking the initial release of Stages and Rotor.

Hugh

 

[FrankDay]

When I was using a Garmin headset on the road and 145mm iCranks I knew that the power I was generating was really about 20% greater than the power I was seeing displayed based upon my testing.

Just for clarification, did you actually run 145mm Icranks on the Velotron while also reading the power output as displayed on the Garmin head unit to come up with this 20% value?

Yes. I did it for a variety of lengths going from 145 to 182.5. I put the Velotron in ergometer mode at a set power and the Garmin on 30s average to get the variance. I assumed the 172.5 reading was "correct" as I was told that the device was calibrated to that length and is supposed to be as accurate as the SRM. It did read about 10 watts higher at this length than the Velotron as the iCranks measure before chain and bearing losses. Anyhow, assuming the chain losses were constant I got a very nice curve showing the cranks gave too high an output beyond 172.5 and too low below 172.5.

You can see it is not quite a straight line as the strain gauges are not at the base of the crank arm so this expected.You can see I saw about 92 watts at 145mm compared to 110 watts when set at 172.5mm, about 18 watts or 20% low.(edit: for some reason I am not able to post pictures so I will post a link to the graph results. http://tinypic.com/r/2dlniux/5

Are you running a Powertap rear wheel in tandem with the Icranks so you can compare to something that's actually validated on the road? Some of the recently introduced power meters have looked pretty good when used on a trainer but not nearly as good on the road.........thinking the initial release of Stages and Rotor.

Hugh

No, this was all Velotron. I don't own a PowerTap. However, I saw nothing to make me think calibration changed on the road.

 

[CoachFergie]

Int J Sports Med. 2006 Jun;27(6):444-7.

Ergometer error and biological variation in power output in a performance test with three cycle ergometers.

Paton CD, Hopkins WG.

Abstract

When physical performance is monitored with an ergometer, random error arising from the ergometer combines with biological variation from the subject to limit the precision of estimation of performance changes. We report here the contributions of ergometer error and biological variation to the error of measurement in a performance test with two popular cycle ergometers (air-braked Kingcycle, mobile SRM crankset) and a relatively new inexpensive mobile ergometer (PowerTap hub). Eleven well-trained male cyclists performed a familiarization trial followed by three 5-min time trials within 2 wk on a racing cycle fitted with the SRM and PowerTap and mounted on the Kingcycle. Mean power output in each trial was recorded with all ergometers simultaneously. A novel analysis using mixed modelling of log-transformed mean power provided estimates of the standard error of measurement as a coefficient of variation and its components arising from the ergometer and the cyclists. The usual errors of measurement were: Kingcycle 2.2 %, PowerTap 1.5 %, and SRM 1.6 % (90 % confidence limits +/- 1.3). The components of these errors arising purely from the ergometers and the cyclists were: Kingcycle 1.8 %, PowerTap 0.9 %, SRM 1.1 %, and cyclists 1.2 % (+/- 1.5). Thus, ergometer errors and biological variation made substantial contributions to the usual error of measurement. Use of the best ergometers and of test protocols that reduce biological variation would improve monitoring of the small changes that matter to elite athletes.

 

[FrankDay]

Int J Sports Med. 2006 Jun;27(6):444-7.

Ergometer error and biological variation in power output in a performance test with three cycle ergometers.

Paton CD, Hopkins WG.

Abstract

When physical performance is monitored with an ergometer, random error arising from the ergometer combines with biological variation from the subject to limit the precision of estimation of performance changes. We report here the contributions of ergometer error and biological variation to the error of measurement in a performance test with two popular cycle ergometers (air-braked Kingcycle, mobile SRM crankset) and a relatively new inexpensive mobile ergometer (PowerTap hub). Eleven well-trained male cyclists performed a familiarization trial followed by three 5-min time trials within 2 wk on a racing cycle fitted with the SRM and PowerTap and mounted on the Kingcycle. Mean power output in each trial was recorded with all ergometers simultaneously. A novel analysis using mixed modelling of log-transformed mean power provided estimates of the standard error of measurement as a coefficient of variation and its components arising from the ergometer and the cyclists. The usual errors of measurement were: Kingcycle 2.2 %, PowerTap 1.5 %, and SRM 1.6 % (90 % confidence limits +/- 1.3). The components of these errors arising purely from the ergometers and the cyclists were: Kingcycle 1.8 %, PowerTap 0.9 %, SRM 1.1 %, and cyclists 1.2 % (+/- 1.5). Thus, ergometer errors and biological variation made substantial contributions to the usual error of measurement. Use of the best ergometers and of test protocols that reduce biological variation would improve monitoring of the small changes that matter to elite athletes.

I guess I don't quite understand the usefulness of this study or what the researchers were trying to do. As if researchers didn't already know that they should use reliable measuring equipment and good test protocols. Of course, because of such issues is the reason statistics were "invented" to help sort out the wheat from the chaff when data isn't "perfect". I did find it interesting that somehow the PowerTap tested more reliable than the "gold standard" SRM, for what it is worth (not much, me thinks).

 

[coapman]

I did find it interesting that somehow the PowerTap tested more reliable than the "gold standard" SRM, for what it is worth (not much, me thinks).

I know nothing about the workings of powermeters etc, will all PowerTaps give the exact same result ?

 

[FrankDay]

I know nothing about the workings of powermeters etc, will all PowerTaps give the exact same result ?

No, although, for all practical purposes, they will all be good enough.

 

[FrankDay]

Well, it looks like Vector has finally made it to market, although I am not sure what that the user will get anything more than true left right power and the ability to switch between bikes reasonably easily for their $1700.

http://sites.garmin.com/vector/

I will get a set and put them through their paces (looking at accuracy, compared to Velotron, and comparing them to our own, soon to be available (I hope) iCranks).

 

[sciguy]

Ray put up a really nice quick review after having a set for 24 hours. They look pretty nice at first blush.

http://www.dcrainmaker.com/2013/08/hands-on-garmin-vector.html

It looks as if there is way more planned than just right left power from these too.
They will work with cranks from 110mm to 220mm so that sure is a plus for crank length experimenters.

Hugh

 

[FrankDay]

They will work with cranks from 110mm to 220mm so that sure is a plus for crank length experimenters.

Hugh

Several years ago when these were announced at Interbike I excitedly contacted Clark Foy and told him he needed to incorporate the ability to use various crank lengths including very short cranks. He apparently listened to me (although I think a few may end up going shorter than 110), and to others I suppose. Right now the ability of the PM is not much of an advance. It looks like they are planning more, according to DCrainmaker, but until they incorporate the ability to actually measure technique I think these will only constitute a small advance over ordinary PM's. I look forward to trying them.