power meter accuracy

[karlboss]

Hi guys,
Does anyone have values for accuracy of the major power meters going around. In an ideal world it would be presented as a table, with manufacturer claimed accuracy, and measured accuracy by an independent party. I just want the numbers.

karl

Numbers i have
claimed measured
powertap +/-1.5%
SRM pro +/-2%
SRM science +/-0.5%
quarq +/- 2%
ergomo +/-0.5%
polar +/-10%inst 2.5 avg
ibike ?

have i missed any?

 

[elapid]

You seem to have all the accuracies well summarized. There may be a difference in some of the PowerTap models, with bigger ranges in the cheaper models? The accuracy is probably not as important in terms of raw power measurements. The accuracy is important in terms of reliability in being able to compare your power outputs from ride to ride. I think SRM, PowerTap and Quark are all reliable, Ergomo and Polar have some issues, and iBike can be unreliable.

 

[nightfend]

It's not really accuracy that matters anyway, it's consistency of the readings on a daily basis.

Comparing your power readings with other riders is pointless.

 

[ElChingon]

Comparing your power readings with other riders is pointless.

Yet is done forever! You could calibrate a power meter incorrectly and record earth shattering numbers, heck you'd expect a ProTour contract, but one proper calibration and its back to mere mortal numbers

 

[Black Dog]

The only thing that matters is the consistency from ride to ride so that you can chart your progress. Comparing to other riders is not effective unless all the meters are running from the same baseline. That being said, well calibrated meters can allow comparison between riders. To calculate my power without a meter I just multiply my mass in grams by the speed that I am riding + the year that I am riding in...

 

[St. Elia]

Well, I have an ibike and I get odd numbers sometimes, like really high numbers or a lot of 0's at other times. But, it gives me a general Idea about what sort of watts I'm producing and it is good enough to base my workouts on. Having said that if I were going to do it again I would have bought a powertap, no questions.

An Australian Mag called ride did a review of all the power meters that you have listed and basically supported what you have listed. They used a calabrated SRM as the base and tested every thing against it. The powertap was almost dead on, the polar was the worst and the ibike a little bit better and close to the ergomo. The powertap was almost indistinguishable to the srm and at thousands less!!

Hope that helps, sorry I gave away the mag to a friend trying to convince him to buy a Powertap

 

[karlboss]

thanks guys. i think i'll see how i get by with a heart rate monitor for a season and if i show required commitment, get something with reasonable accuracy.

 

[davidg]

Well, I have an ibike and I get odd numbers sometimes, like really high numbers or a lot of 0's at other times.

You sound surprised. How good is it on the ergo?

I have a PT and it compares well with any SRM's I have used and as you say, a fraction of the price.

 

[St. Elia]

You sound surprised. How good is it on the ergo?

I have a PT and it compares well with any SRM's I have used and as you say, a fraction of the price.

Don't know what you mean by ergo?

The thing is the ibike does work as it gives you a ball park figure and it is super light and can be transferred between bikes, which for me is important. If you have one bike and want to get a power meter I would get a cheaper PT for sure.

For the original poster, trust me if you are unsure how committed to training you are and want to make the most of your training, get a power meter. For me it has changed the way I train and I no longer over train and know exactly how hard to train for intervals. Also I can tell how much I have improved either within the season or from one year to the next. I am happy to say that I have an extra 20 watts this year and i would know that with a HR monitor. Get a few books and you will be convinced. Start training with power and you will wonder why you wasted your time all those years

 

[James Jordan]

Well, I have an ibike and I get odd numbers sometimes, like really high numbers or a lot of 0's at other times. But, it gives me a general Idea about what sort of watts I'm producing and it is good enough to base my workouts on. Having said that if I were going to do it again I would have bought a powertap, no questions.

An Australian Mag called ride did a review of all the power meters that you have listed and basically supported what you have listed. They used a calabrated SRM as the base and tested every thing against it. The powertap was almost dead on, the polar was the worst and the ibike a little bit better and close to the ergomo. The powertap was almost indistinguishable to the srm and at thousands less!!

Hope that helps, sorry I gave away the mag to a friend trying to convince him to buy a Powertap

The mag in question is called RIDE and they did the test here in Canberra. They also made a major mistake with their testing protocols. Firstly they did not weight the chain but used the manufacturers ave weight. Dura Ace chains can be plus or minus 15g from this value and it will though off the readings. Secondly they did not measure the chain stay correctly, which again will through off the readings.

I have two Polar power units and have put both up against a power tap wheel and found them to within 5-6 watts. Polar units do have three problems, but are all easy to manage. They are really fussy with batteries. The only ones that I have managed to get a ongoing reliability with are Energizer Lithium. Also the chain speed sensor on the rear derailleur is susceptible to getting guncked up and needs to be cleaned regularly. Lastly then tend to be unreliable when used with trainers. Both of mine tend to read 50-60 watts low with lots of fluctuation, but as I hate using a trainer this does not bother me much.

I will admit that I would love a SRM, but the cost is prohibitive. The Powertap just not cost effective as I would need to get 4 hubs to cover all my wheels. Plus there is no one who can service them her in Australia.

 

[davidg]

Don't know what you mean by ergo?

Sorry, static trainer, mag trainer etc