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Thread: Power meters

  1. #1
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    Power meters

    Have started to look at power meters for my ride and I was wondering
    which is the better way to go?

    Power cranks or hubs saw a great deal on some sram power cranks
    but have read alot about the power tap hubs. Is there a differance of is it preferance?

    the obviously all do the same thing so watt is the best way to go?

    Is power the best way to train?

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  2. #2
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    Your questions have been answered many times over, but I'll add that I have a Quarq, and I wish that I had an SRM or Powertap because the zero offset on the Quarq is flakey.
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  3. #3
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    IMO, the best powermeter is an Ant+ Powertap. Its cheap, has built in speed and cadence and you can do most of the service to it yourself. I know its heavy(er) and you can't use fancy wheels with it (unless you build it in an ENVE rim) but for most people it will be more than enough. SRMs are money pits, Quarqs are fussy (but getting better) and there is really no other reliable option.

  4. #4
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    Quote Originally Posted by kbiker3111
    Its cheap, has built in speed and cadence
    Just as a little quibble: Yes, the Powertap can transmit cadence data, but since it guesses these data from the torque fluctuations while pedaling, the cadence estimates it transmits are fairly lousy, to the point of being close to useless. Mind you, I don't think there's anything wrong with Powertaps, but having a separate cadence sensor is a good idea.

  5. #5
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    Quarq zero offset

    Can you describe what you mean by it being "flakey" ?

    Thanks
    power1369

  6. #6
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    Quarqs aren't fussy at all; and SRM's are pricey but very solid. Powertaps are by far the most service heavy PM. Saris does give good service though.
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  7. #7
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    IMO, crank based is the way to go. I love my SRM, it works perfect, I just solder in a $20 battery once a year and its ready to go. Plus, SRMs can be picked up very cheap on ebay.

    A Quarq would be nice too though, being able to swap the battery in 30 seconds would be nice versus the 30 minutes it takes to change the SRM battery

  8. #8
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    I'm Quarq user with a Garmin 500. I find it quite accurate and easy to use. Zeroing out is just pedaling backwards for 4 revolutions.
    For my next trick I will now set myself on fire!

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    I have a Quarq and love it. I don't have any zeroing problems like the other poster. Also like that don't have to send it back to the factory to replace the battery. (You have to do that with SRM.)

  10. #10
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    Quote Originally Posted by Juanmoretime
    I'm Quarq user with a Garmin 500. I find it quite accurate and easy to use. Zeroing out is just pedaling backwards for 4 revolutions.
    The issue with the Quarq's "auto zero" function is that when you turn your cranks backwards the system assumes a basic drive train efficiency. If your bike is more or less efficient than that assumed by the Quarq your power readings will be incorrect. This isnt an issue if you manually zero the system.

    I think just about any of the "big 3" power meter options are fantastic. I prefer the SRM because you can calibrate the unit using know weights without sending it back to the factory like the Quarq or PT (Quarq has an Iphone app for recalibration coming out soon)

    The major drawback with the Quarq was the need to use a Garmin as a head unit. With the new firmware updates you can use the SRM PC7 head unit. In my experience the Garmin units are terrible if you want reliable power data. They suffer from a lot of drop outs and have a tendency to delete all of your data when you push the lap button.

    Pairing a Powertap Joule with either the Quarq or SRM is another great option as long as you have a speed sensor that works 100% of the time. The Joule stops recording if you dont run a speed sensor with the system. This is not an issue with the PT hub.

    My personal favorite setup is an SRM with a PC7. Super reliable, easy to maintain.

  11. #11
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    I got my SRM off ebay a while back for a good price and love it. You don't have to send it back to get the battery replaced if you can solder in a new battery yourself (very easy since the battery in mine is just soldered to some wires so you can pull it all out).
    I think crankbased power is the best option at the moment, you can swap to a beater wheel for the trainer, decent wheels for training or race wheels and you will always be able to collect data.

  12. #12
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    Quote Originally Posted by power1369
    Can you describe what you mean by it being "flakey" ?

    Thanks
    power1369
    It seems to need re-calibration whenever there's a change in temperature, and, like Chase said, the pedaling backwards thing is not totally accurate. That means that on a 5 hour ride in Memphis' current spring weather, the temperature will go from 40-65, and I'll end up stopping to re-calibrate my powermeter at least 4 times. It's incredibly annoying.
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  13. #13
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    Sorry to hijack this thread, but I have a question. Would the most ACCURATE power meter be one that measures as close as possible to where the rider applies power to the drive chain....i.e. the crankset/bottom bracket? A Powertap measures from the rear hub, and I'm thinking that some of the wattage inputted in the pedals will be lost as it is transferred by the chainrings, chain and cassette to the rear hub? Check this one out http://www.metrigear.com/products/

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    Quote Originally Posted by G**G
    Sorry to hijack this thread, but I have a question. Would the most ACCURATE power meter be one that measures as close as possible to where the rider applies power to the drive chain....i.e. the crankset/bottom bracket? A Powertap measures from the rear hub, and I'm thinking that some of the wattage inputted in the pedals will be lost as it is transferred by the chainrings, chain and cassette to the rear hub? Check this one out http://www.metrigear.com/products/
    It's really meaningless where you get the number. The percentage of power lost in the drive train is pretty much constant, so all that loss would mean is that you would get slightly lower numbers if you measured at the hub vs. at the pedals. You're not trying to determine the amount of power you apply to the pedals within a couple of % but rather your power output so you can train better. The conclusions regarding training will be the same whether the power is measured at the pedals, the cranks, or the rear hub.

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    I'm waiting for the Garmin Metrigear Vector. I think it will be the next big thing in Power Meters. Not sure how the Polar/Look one will go, but perhaps good also.

  17. #17
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    With Metrigear being acquired by Garmin there is no telling when they will be coming out with the Vector. Also Garmin/Metrigear's other pedal spindle option looks promising but once again no telling what the time frame will be.

  18. #18
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    Quote Originally Posted by Pirx
    Just as a little quibble: Yes, the Powertap can transmit cadence data, but since it guesses these data from the torque fluctuations while pedaling, the cadence estimates it transmits are fairly lousy, to the point of being close to useless. Mind you, I don't think there's anything wrong with Powertaps, but having a separate cadence sensor is a good idea.
    Uh, its totally useful for me. It seems accurate to 5 rpm under 120 rpm and if you have power, cadence because relatively useless anyway.

  19. #19
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    Quote Originally Posted by kbiker3111
    Uh, its totally useful for me. It seems accurate to 5 rpm under 120 rpm
    It's accurate, and can be accurate only if you are pedaling at a nice and even stroke, constant rpm, and don't do weird stuff like pulling on your pedals, accelerating or decelerating, etc. If you do any of these, it will give you random numbers. But, yeah, rpm is not too important, and apart from the random spikes it can still give you a rough idea of your cadence.

  20. #20
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    Quote Originally Posted by chase196126
    ... In my experience the Garmin units are terrible if you want reliable power data. They suffer from a lot of drop outs and have a tendency to delete all of your data when you push the lap button. ... .
    I'm not seeing any problems whatsoever, with Garmin Edge 500 (v2.6 firmware) and a 2010 Powertap Elite+ hub.
    I am using WKO+ v3 software for analysis.

    Garmin v2.60 now has ability to measure & display actual torque applied to the powermeter, as a linearity/fullscale check (so-called "stomp test"). There's a convenient calculator near bottom of this webpage:
    http://www.cyclepowermeters.com/powe...check-76-c.asp

    What Garmin calls "calibrate" is really just a zeroing ... autozero & manual zero both available in Edge 500.
    Last edited by tom_h; 03-18-2011 at 01:13 PM.

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