Cyclometer sensor position question

Discussion in 'Cycling Equipment' started by Andrepaul, Nov 13, 2005.

  1. Andrepaul

    Andrepaul New Member

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    I just bought a new VDO, wireless cyclometer and I'm wondering what the optimum sensor/magnet position is on the fork (i.e. how far up from the bottom of the fork) since the instructions don't specify this. I want to set this up for the greatest accuracy.
    Thanks
     
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  2. scotty72

    scotty72 New Member

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    Shouldn't matter as the outside of the wheel spins at exactly the same rate as the inside.
     
  3. Re-tread

    Re-tread New Member

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    Hi Andrepaul,



    The magnets are very powerful for their given size these days, so the sensor will pick up the movement very readily. Don’t be too worried about getting the sensor really close to the spokes/magnet, just make sure it’s path of movement runs close as possible to the center of the sensors length.



    There’s no real difference whether you place the sensor and magnet close to the rim or the hub, as the magnet will pass the sensor at the same time regardless of positioning. The real factors are the time it takes for the magnet to pass the sensor, which is quicker at the rim end, and the centripetal forces, which are greater at the rim end also. Myself, I prefer to position the magnet about 10-15 cm from the centre of the hub (Assuming wheel size is 700) and then position the sensor (Should have a mark or groove midway on its length) accordingly. POSITION THE MAGNET ON A SPOKE OPPOSITE THE VALVE as this will tend to balance out the weight of the valve a little.



    I’m not trying to make you to suck eggs here, but, additionally, run a tape measure carefully around the circumference of the tire. Start measuring at the 10cm mark on the tape and then deduct the 10cm off (Retractable tape measures have bad ends) after you have attained an average of 3 recordings (so do it 3 times). This will then be the closest measurement of your true wheel circumference un-loaded. My Cateye was factory set to 2096mm, my measurement was actually 2126, essentially it would have been out by about 1%. But 1km in every 100kms makes a difference to me.



    Have fun.

    ;)
     
  4. Andrepaul

    Andrepaul New Member

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    Hey Re-tread... thanks for the tips. I'll try them.
     
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