Bicycle Power Meters + POLL

tom231

I'd like to know what people think to using power meters for training.

Has anyone got any advise for people wanting to buy one ? I know they are becoming more and more popular but still only a minority of cyclists use one. How come ? (that's what the poll is for)

Any comments / thoughts would be much appreciated.
Thanks, tom.

DaveyL

For me, they are probably a bit too pricey right now - at least the SRM, Ergomo and PowerTaps. I've promised myself one as a reward if I can drop a few more kilos though! For those who splash out 2.5k upwards for a bike, I wouldn't have thought cost was an issue. I would rather spend, say 1.5 - 2 grand on a bike plus a PowerTap than get a blingier 2.5 - 3 grand bike. I think I would get a lot of useful info out of a powermeter on the road, and it would be perfect for doing intervals on the turbo.

azzerb

A lot of people spend that much and more on wheels. I'd much rather buy a power meter than new wheels worth that much.

As said above, £2k bike + power meter is much better than a £3k bike.

I use power to train at the gym, however, I'd love to have a power meter on my bike. Maybe a future buy summer 2009.

If you lose the weight, and you can afford it, then I'd go for it, make sure you read up on the power books (to make the most of your investment) and enjoy.

Alex_Simmons/RST

I already have 3 powertaps and 2 SRMs.
and I can't ride at the moment

I can understand the cost for many would be an inhibitor but not for those that spend big $ on their bikes/wheels when it's their engine that needs work. The #1 performance enhancer is training. By a long shot.

Now you don't need a power meter to get fitter (you train well to do that) but it will sure help short cut the process of finding out the optimal way of doing so and teach you things about yourself that others have taken many years if not decades to learn.

Power meters don't suit everyone though. You do need to take some time to learn how to use them effectively and hence require a little time investment on your part (or invest in someone else to help you). No point if all you are going to use it for is an over price cyclocomputer. But now there are some great sources of info available for the price of a round of coffees. A few years back, such info was not generally available.

As a tool to enhance the athlete-coach relationship - it is simply fantastic.

Kléber

It all depends on what you want from your cycling. If you're able to train yourself properly using traditional methods like heart rate and got your weight right down and still find you're coming up a few seconds short against others, then using the PM can help you to target your workouts even more.

But you risk turning each training ride into a work session, the constant need to follow the screen makes a ride become a job.

By all means use one but I'd only recommend it once you are full able to master the theories behind power training, just buying one isn't going to make you faster.

bahzob

Have a Powertap and Ergomo. Of the two I prefer the Ergomo because its head unit has more functionality, it seems a bit more reliable and in practice its easier to use with different bikes or same bike/different wheels.

dennisn

When heart rate monitors first came out they were billed as the "Ultimate" training
tool and even the lowlyest of racers and riders were just plain foolish to ride without
one. Now it's power meters and the advert's are pretty much the same and heart monitors
have even been put down as not really useful by power meter marketing people.
So what's the next got to have, can't live without, piece of equipment we need to buy
that we can't possiblly ride or even live without???? Should be interesting.
Anyway that's my opinion.

Dennis Noward

tom231

Dennisn, i can see your point there but i also understand why power meters are very useful for training. I agree with what daveyl and azzerb say in that if you factor in the price of a power meter into the cost of a new bike its not that bad.
It seems too that just buying a power meter isn't enough, you have to learn how to train with power effectively and that can be done easily with the right guidence. I have also found that you can hire power meters for not a great cost and you could just get one for like january through to april which i assume are the only months when you would really benefit from having one. Thats what i'm thinking of doing.

DaveyL

dennisn wrote:

When heart rate monitors first came out they were billed as the "Ultimate" training
tool and even the lowlyest of racers and riders were just plain foolish to ride without
one. Now it's power meters and the advert's are pretty much the same and heart monitors
have even been put down as not really useful by power meter marketing people.
So what's the next got to have, can't live without, piece of equipment we need to buy
that we can't possiblly ride or even live without???? Should be interesting.
Anyway that's my opinion.

Dennis Noward

Probably you're partially right in terms of the marketing, but it may also reflect the level sports science was at then and now.

cervelorider

dennisn wrote:

When heart rate monitors first came out they were billed as the "Ultimate" training
tool and even the lowlyest of racers and riders were just plain foolish to ride without
one. Now it's power meters and the advert's are pretty much the same and heart monitors
have even been put down as not really useful by power meter marketing people.
So what's the next got to have, can't live without, piece of equipment we need to buy
that we can't possiblly ride or even live without???? Should be interesting.
Anyway that's my opinion.

Dennis Noward

Well, I think that surgery will play a big part, by using sensory inplants within the muscles that can then be sent to a screen, giving a breakdown of what is happening at a metabolical level within the muscle tissue.
This will run along side current power metering to give an even more accurate analysis of how training is going.
After that, there will be muscular inplants allowing individuals to upgrade their untrained, or semi-trained muscles for pro-level muscle groups and so on, and so on.

I'm already signed up with SRM, along side a select few who have given consent to be guinea pigs in testing some of the ideas that I've outlined above.......

Watch this space

Mike Willcox

cervelorider wrote:

dennisn wrote:

When heart rate monitors first came out they were billed as the "Ultimate" training
tool and even the lowlyest of racers and riders were just plain foolish to ride without
one. Now it's power meters and the advert's are pretty much the same and heart monitors
have even been put down as not really useful by power meter marketing people.
So what's the next got to have, can't live without, piece of equipment we need to buy
that we can't possiblly ride or even live without???? Should be interesting.
Anyway that's my opinion.

Dennis Noward

Well, I think that surgery will play a big part, by using sensory inplants within the muscles that can then be sent to a screen, giving a breakdown of what is happening at a metabolical level within the muscle tissue.

Watch this space

I've got one of those already. In fact i've had it for years. It's called Perceived Exertion.The screen is in my eyes and when I get to peak power it glows like a red mist

dennisn

cervelorider wrote:

dennisn wrote:

When heart rate monitors first came out they were billed as the "Ultimate" training
tool and even the lowlyest of racers and riders were just plain foolish to ride without
one. Now it's power meters and the advert's are pretty much the same and heart monitors
have even been put down as not really useful by power meter marketing people.
So what's the next got to have, can't live without, piece of equipment we need to buy
that we can't possiblly ride or even live without???? Should be interesting.
Anyway that's my opinion.

Dennis Noward

Well, I think that surgery will play a big part, by using sensory inplants within the muscles that can then be sent to a screen, giving a breakdown of what is happening at a metabolical level within the muscle tissue.
This will run along side current power metering to give an even more accurate analysis of how training is going.
After that, there will be muscular inplants allowing individuals to upgrade their untrained, or semi-trained muscles for pro-level muscle groups and so on, and so on.

I'm already signed up with SRM, along side a select few who have given consent to be guinea pigs in testing some of the ideas that I've outlined above.......

Watch this space

Can you get me signed up. Maybe they need an older guy like me. In any case not much
is helping me now. So what have I got to loose???
Dennis Noward

Alex_Simmons/RST

Kléber wrote:

But you risk turning each training ride into a work session, the constant need to follow the screen makes a ride become a job.

Or alternatively, it can tell you which rides you enjoy doing are useful training, and which are not (and so you can adjust accordingly) depending on your goals. There is no need to follow the screen constantly.

Kléber wrote:

By all means use one but I'd only recommend it once you are full able to master the theories behind power training,

You don't need to master the theories, in the same way you don't need to be an expert in physiology to become a good bike rider. But the more knowledge you gain, the greater value you can gain from the tool. There are sensible training practices that power meter data will help ensure you are following.

Kléber wrote:

just buying one isn't going to make you faster.

"The PowerTap is a tool, not a bolt on motor " - Chris Mayhew

The power meter is a bit of a truth meter and some people don't like the truth.

Kléber

Alex_Simmons/RST wrote:

You don't need to master the theories, in the same way you don't need to be an expert in physiology to become a good bike rider. But the more knowledge you gain, the greater value you can gain from the tool. There are sensible training practices that power meter data will help ensure you are following.

I agree but many dash to buy one and then don't understand them. It's a tool and a complicated one as it's not understanding what the screen says that matters, it's what's happening to your body that counts. So no need for a sports science doctorate but I'd recommend reading plenty of forums for information for power and being familiar with the training principles here before you buy the kit.

Alex_Simmons/RST

Or spend about the same as 3 cups of coffee on the book "Training and Racing with a Power Meter" by Allen & Coggan and that'll cover just about all that any power newbie will need and more. It provides basic no nonsense info for the pre-power user through to more esoteric info for the experienced user.

But a good start are the power training forums and this site:
http://www.trainwithpower.net/
which is loaded with lots of good links and plenty of free info.

Training with power based principles does not require a power meter. It is just good sensible training specific to the rider's goal(s) of the sort that I'm sure Mike advocates (despite his aversion to the tool). However having a PM will ensure that you are actually following those sensible principles. It is quite amazing how far away from good training many get and how much they learn once they have a PM and see what's really been going on.

synchronicity

I'd like to suggest other poll options:
- I can't be bothered.
- something that's not needed for people training but not racing.
- they add complexity to the bike

I'd tick all 3. Previously I owned a power meter with the S710. I found after the initial "Gee whiz, look at all the readouts" phase, I just didn't enjoy riding anymore & I became a slave to the hrm.

Oh yeah, and it didn't help when I was overtaken by a guy who didn't even have a speedometer. These days I ride a bike without anything on the handlebars. I'm still not any fitter though.

tom231

So i agree with most people on here when they say that power meters are a very useful training aid once you know how to use one, but which power meter to get ?

I've found loads of info on the main few (SRM, Ergomo and PowerTaps) but does anyone know how Polar's Power Output Sensor works ? Does it have strain gauges that measure the strain across the chainstay or what ?

Alex_Simmons/RST

tom231 wrote:

So i agree with most people on here when they say that power meters are a very useful training aid once you know how to use one, but which power meter to get ?

I've found loads of info on the main few (SRM, Ergomo and PowerTaps) but does anyone know how Polar's Power Output Sensor works ? Does it have strain gauges that measure the strain across the chainstay or what ?

The Polar measures the speed of the chain (using optical sensors at the dereilleur) and the vibration frequency of the chain under load (think of a guitar string analogy) with a sensor mounted on the chainstay.

The greater the tension on the chain, the higher the frequency (e.g. tuning your guitar). If you know the weight of the chain and its length (i.e. the chain stay), then along with the chain speed you can infer the power since power (W) = chain tension (N) x chain velocity (m/s).

It's quite a clever solution but is not suitable for everyone (as are all PMs). It does require some care in installation and set up and very often they don't work on turbo trainers as the trainer vibrations mess up the frequency of signal picked up by the chain stay sensor.

Older polars recorded with a 5 sec sample rate. The newer model records with a 1 sec sample rate but has limited memory capacity which means that it'll only store 2 hours or so of data at 1 sec sampling before it reverts back to 5 sec rate.

I prefer my clients to use PTs or SRMs but have clients with all the systems mentioned.

ergomos have some great features, especially with their CPU, but the one "feature" that lets them down the most is the inability to check its calibration independently. IOW you need to use another power meter (PT or SRM) to validate the ergomo's accuracy. They also only actually measure the power of the left leg and double that. That for example would be completely useless for someone like me who now has a significant leg imbalance.

bahzob

Alex_Simmons/RST wrote:

tom231 wrote:

ergomos have some great features, especially with their CPU, but the one "feature" that lets them down the most is the inability to check its calibration independently. IOW you need to use another power meter (PT or SRM) to validate the ergomo's accuracy.

? Never heard that before. I have an Ergomo and it came with an independent (German testing lab, which IMO means its probably pretty trustworthy), individual certificate of calibration comparing its readings (at 100W, 525W and 1000W) with a standard test device (got nothing like this with my Powertap). Accordingly I was more inclined to test my Powertaps accuracy with the Ergomo, not the other way round. Can you explain a bit more on why I should trust the Powertap and not the Ergomo?

Also quick rant on head units. Powertaps wireless one costs £195 (so dont drop it like I did). For this price you only get 3 display figures, no simultaneous display of actual and average watts (the Ergomo has this and for my money this makes it a better buy) and a useful design feature that requires you to use both hands to set intervals/refind your Ptap after a stop (and in the latter case will delete all your ride data if you press the same buttons too long).

Also both Ptap and Ergomo dont have the ability to set power target training zones, a standard feature (for HR natch) on HR computers for years.

Alex_Simmons/RST

The ergomo might have been accurate when installed on their test rig but they are very sensitive to installation in the field and as such the power readings once installed on your bike may be perfect or maybe considerably out. A poorly faced bottom bracket, the sensor not being absolutely correctly aligned and so on can easily throw them off.

The problem is that there is no way to check the calibration of an ergomo once it's installed on your bike. The user is left in the dark as to whether or not the unit is providing accurate data and whether the calibration number once installed is correct or needs tweaking. You have to compare it to another known and calibration checked power meter or ergometer (which is exactly what ergomo do).

For instance, I have a client with an ergomo and a calibration checked powertap. The 'mo reads15% low, even though the factory calibration settings were used. He is no mechanical dill either and knows how to set things up on bikes.

Now the usual argument is - "as long as it's consistent then it'll show my relative fitness changes etc", which is completely true, until you need to upgrade, change meters etc. Then what?

Alex_Simmons/RST

bahzob wrote:

I have an Ergomo and it came with an independent (German testing lab, which IMO means its probably pretty trustworthy), individual certificate of calibration comparing its readings (at 100W, 525W and 1000W) with a standard test device (got nothing like this with my Powertap).

Just because it's German you trust it? :shock:

How independent is that lab? Presumably they are paid by ergomo. :?:

At least with a Powertap and an SRM you can conduct a calibration check yourself to know whether or not the unit is within tolerances once it's on your bike. With an SRM you can then change the calibration setting yourself if required. If a PT is outside of tolerance, then it has to be sent back to Saris for recalibration (or replacement).

Jeff Jones

I have an Ergomo so this is an excellent excuse for my 'low' power readings ;-)

But I'll be able to test it against a PT soon, and I have a feeling it will be fairly close.

Alex_Simmons/RST

Jeff Jones wrote:

I have an Ergomo so this is an excellent excuse for my 'low' power readings ;-)

But I'll be able to test it against a PT soon, and I have a feeling it will be fairly close.

And then what creative excuse will you come up with

I have another 'mo using client and while he is confident it reads correctly (it is certainly consistent), for his size his CdA as calculated using his power meter data is exceptionally low (< 0.2). Now it's possible it may be correct but it's a little red flag for me.

There are many, many happy 'mo users out there though!

bahzob

Alex_Simmons/RST wrote:

bahzob wrote:

I have an Ergomo and it came with an independent (German testing lab, which IMO means its probably pretty trustworthy), individual certificate of calibration comparing its readings (at 100W, 525W and 1000W) with a standard test device (got nothing like this with my Powertap).

Just because it's German you trust it? :shock:

How independent is that lab? Presumably they are paid by ergomo. :?:

At least with a Powertap and an SRM you can conduct a calibration check yourself to know whether or not the unit is within tolerances once it's on your bike. With an SRM you can then change the calibration setting yourself if required. If a PT is outside of tolerance, then it has to be sent back to Saris for recalibration (or replacement).

Just for the record the certificate that comes with the Ergomo is issued by an accredited lab and I am sure they are independent. I mentioned that they are German simply because the country has a well justified reputation for engineering excellence and a lab based there should be trusted to carry out tests reliably and independently (no I am not German nor work for Ergomo)

One output of the test is a unit specific offset value that needs to be checked following installation (and ideally before each ride). This checking procedure seems very similar to the Powertap process and not sure how the Powertap is better in this respect. But happy to be corrected.

All this said I am interested in this feedback and since I have both a Powertap and Ergomo will carry out at test at some point to see how they compare, if I can come up with a valid protocol (since the reason for getting the Ergomo in the first place was to use with bikes that could not take the Powertap wheel.)

bahzob

Seems already been a test Ergomo vs Powertap done by Hunter Allen and written up by a third party here:

http://mywebpage.netscape.com/rechung/wattage/ergomo/ergomo-pt.html

Concluded that the two were consistent.

BTW Same source also has results of a separate test comparing Powertap/SRM/Polar when all three mounted on same bike.

http://mywebpage.netscape.com/rechung/wattage/rosetta/rosetta.html

cervelorider

I do like the idea of having constant power and average power - re ergomo.

As for german engineering, the SRM protocol for calibrating slope on ther PM's is about as basic as it gets, in contrast to the price you pay for the whole system.
IIRC, Bob Tobin has created a far more accurate system for calibrating the SRM slope.

All the PM systems have glitches, and there are good and bad points to all of them, just give it a few years and everyone will have one - even Mike and Ruth

Jeff Jones

Alex_Simmons/RST wrote:

Jeff Jones wrote:

I have an Ergomo so this is an excellent excuse for my 'low' power readings ;-)

But I'll be able to test it against a PT soon, and I have a feeling it will be fairly close.

And then what creative excuse will you come up with

Don't worry, I'm a bike rider and can always come up with an excuse ;-)

The current one is "I am lazy and need to do some lactate tolerance training" which should last me a month or two.

bahzob

Elswhere on this forum
http://www.bikeradar.com/forum/viewtopic.php?p=14777396#14777396

points to an article in a German cycling magazine (in English) that gives an example of why they can usually be trusted to be thorough when it comes to testing

http://www.conti-tyres.co.uk/conticycle/road_tyres/attack%20force/Resistance%20Fighters.pdf

Hopefully same source may do a test on power meters soon.

Alex_Simmons/RST

bahzob wrote:

All this said I am interested in this feedback and since I have both a Powertap and Ergomo will carry out at test at some point to see how they compare, if I can come up with a valid protocol (since the reason for getting the Ergomo in the first place was to use with bikes that could not take the Powertap wheel.)

Well you are well placed to have confidence in your ergomo's readings since there is no way to check the calibration of an ergomo without reference to another meter:

i. Validate the PT using the testing protocol, see here:
http://www.midweekclub.ca/powerFAQ.htm#Q23
I would do this over a couple of gear combinations and both cranks.

ii. As long as the PT meets spec, then compare it to the ergomo readings. A few road rides and a session on a turbo at various wattages should be enough. The ergomo should read a little higher than the PT (~2%) to account for drivetrain losses.

However, if you have any leg imbalances, then it may show up as the ergomo only reads left leg and doubles that. One way to check it is to pedal with your left leg only on a trainer. The ergomo should be exactly double the PT reading. However, leg "imbalances" are not necessarily properly identified with isolated leg pedalling.

If the ergomo is out then you have two options AFAIK:

I. adjust the slope value (K-factor).
adjusting the K-factor may however mean the readings are close at one power level but not at others. (If this is required I'd suggest getting them to be consistent at race wattages)

II. adjust the angle of the bottom bracket sensor wires (say between 8 to 10 o'clock)


Comparing point to point data from each PM is not straightforward though as:
a) each PM uses different data sampling intervals and both are subject to aliasing* of power data (the ergomo actually suffers a little more from this effect than the powertap but it exisits in both)
b) timing synch offsets can readily occur in the data (e.g. the recording does not start at precisely the same time and stoppages are handled differently)


* aliasing: http://en.wikipedia.org/wiki/Aliasing
essentially the tendency for the recorded / displayed power data to be a lot choppier than it really is, since the torque sampling is conducted over a fixed time interval - each interval contains a different (fractional) number of pedal strokes which means one interval might have three torque peaks and the next interval might only have two torque peaks. It makes the recorded power look choppy. It all evens out over time of course. SRM doesn't have an aliasing effect as its torque samples are averaged over a whole pedal stroke.

bahzob

Thanks for above. Has got me intrigued. So since I had a turbo session planned last night I amended it a bit to carry out a rough and ready comparison of Powertap vs Ergomo. Did 3x40 minute sessions each comprising
- 100W-270W ramp increasing 10W/minute (= my rest>endurance>tempo zone)
- 3 mins at 270W
- 4x5 minutes 1-260W, 2-250W, 3-240W, 4-250W.
(Chose these values as using Ergomo on fixed so used for endurance/tempo so its the range I am most concerned about being correct.)

First and last intervals done using Roubai/Powertap, middle with Langster/Ergomo

I assumed if power same for all 3 intervals then HR and RPE should also be comparable. Obviously monitored RPE but deliberately kept HR hidden so it would have no influence. On the Roubaix I used a low gear so cadence in same 70-100rpm range as the Langster.

Lots of things could be done to make this more scientific but results seemed to show my Powertap and Ergomo pretty much the same. Kept power constant (TSSs were 42.4, 42.6 and 43.2, power 226W/226W/228W), first Powertap and Ergomo intervals were pretty much identical in terms of HR and RPE, last Powertap felt a bit harder and had higher HR (and a much less smooth power line) but by then getting a bit warm. HR affected by having an interval starting 10bpm higher than first 2.

(see below for WKO graph)
http://bp3.blogger.com/_HA3t_DGwgjw/SAB4hpSPeII/AAAAAAAAAP4/1bz_fZcFSlc/s1600-h/ptapvergomo.jpg

Alex_Simmons/RST

Interesting - can't put 'em on same bike? I think you said one is on a fixed gear bike?

Anyway, they seem to be in reasonable alignment, which is good .

My eye balling shows HR was a bit lower (say 5 bpm) on ergomo for same power as the 1st PT effort? I wouldn't quite expect that.

How did turbo speeds compare?