Sigma Computer Wrong Speed

Discussion in 'Cycling Equipment' started by jwroubaix, Mar 12, 2011.

  1. jwroubaix

    jwroubaix New Member

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    My Sigma computer is reading too fast. I've tried moving the sensor on the front wheel but then it won't read it. Any suggestions?
     
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  2. tafi

    tafi Member

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    It's nothing to do with where the magnet and sensor are located. The magnet will (should) only ever trigger the sensor once per revolution no matter where it is. It is most likely due to the wrong calibration for wheel circumference.
     
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  3. cyberlegend1994

    cyberlegend1994 Moderator

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    ^ Correct. The Sigma computers have a setting for your wheel and tire size, if it's not set right your speed and distance will be way off. Which model do you have?
     
  4. coneofsilence

    coneofsilence Member

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    How do you know that your speed is wrong?
     
  5. Volnix

    Volnix Well-Known Member

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    You can try placing the sensor closer to the hub. In this case the speed that the magnet that will passing by the sensor will be less and there is less of a chance of the computer "missing" a few measurements.
    Then you can also double check it with a gps receiver.
     
  6. tafi

    tafi Member

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    This is a good Question


    The problem here is that the computer reads too fast. If missing the magnet were the problem then the computer would read too slow.
     
  7. Motobecane

    Motobecane New Member

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    this is almost definately a tire size calibration issue. in the setup screen you should have to input your tire size or your instructions will give you a chart with tire size and a number to enter in. That number is the distance your wheels cover in one revolution. whenever I put new tires on i just take a tape measure and roll my bike one revolution and enter that to be certain.
     
  8. coneofsilence

    coneofsilence Member

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    I still what to know how he knows that the speed is wrong.
     
  9. jwroubaix

    jwroubaix New Member

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    Two ways I know my speed is off. one is when I go buy a speed limit signs, it's not even close. Two, I know how far my usual route is, and last time it showed double what it usually is. How do I find out exactly what my wheel size is? I accidently put the computer into a different language so it's very possible that I screwed up the wheel settings. THanks for your help.
     
  10. coneofsilence

    coneofsilence Member

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    Have you tried resetting the computer to get it back on the original language?
    It should say on your tyres what size they are.
     
  11. finnrambo

    finnrambo New Member

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    usually 2124mm isn't it?
     
  12. Motobecane

    Motobecane New Member

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    there is no "usual" what the manf publishes and what the tires actually measure out to re 2 different things, thats why whenever I switch tires I take the extra 20 seconds to take an actual measurement.
     
  13. ambal

    ambal Active Member

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    Dude, have you tried to RTFM ? /img/vbsmilies/smilies/ROTF.gif
     
  14. cyberlegend1994

    cyberlegend1994 Moderator

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    Go by your tire size. I have a model 506 - for example, on mine, according to the manual for 700x23 tires the setting is 2133, for 700x25 it's 2146. Which model do you have? BTW - I have also had one strange thing happen, it appears that the sensor can also pick up stray electromagnetic fields - I rode by a transformer one day a while back and my speed reading shot up to 199.5 MPH. :eek:
     
  15. coneofsilence

    coneofsilence Member

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    Go by your tire size. I have a model 506 - for example, on mine, according to the manual for 700x23 tires the setting is 2133, for 700x25 it's 2146. Which model do you have?

    BTW - I have also had one strange thing happen, it appears that the sensor can also pick up stray electromagnetic fields - I rode by a transformer one day a while back and my speed reading shot up to 199.5 MPH. /img/vbsmilies/smilies//eek.gif

    My heart rate monitor will do that, i'll get home and have a maximum heart rate of 290. My heart would have been screaming like a humming bird.
     
  16. Bob Ross

    Bob Ross New Member

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    The Sigma manual has a list showing the approximate wheel circumference for a large variety of tires. But if you want to find out exactly what your wheel circumference is, you measure it.

    Put a piece of tape on the floor. Stand your bike up with the front wheel valve stem at the 6:00 position (pointing straight up) and line up that valve stem with the leading edge of the piece of tape. Now walk your bike forward for one (and only one) complete revolution of the tire, such that the front wheel valve stem is again in the 6:00 position (pointing straight up) only you're a few feet away from where you started. Put another piece of tape on the ground lined up with your valve stem.

    Now measure the distance between the two pieces of tape.
     
  17. Splendiferous

    Splendiferous New Member

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    I think I am having the same problem. My speed is set to mph but the reading seems more like kmph. Sigma computers used to have a separate size chart if you were using mph vs kmph. This model (the 506) is supposed to do that conversion automatically - but it does not seem to be. You might try using the wheel size from the chart on the older model ( BC 500) .. so a 700x25 tire would be 1333 for mph instead of 2146 for kmph. Or you could divide whatever you think your wheel size should be by 1.61.
     
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