speed sensors and wheel magnets

acidstrato
acidstrato Posts: 945
edited May 2011 in Workshop
wondering if it makes a difference where you position the magnet on the spoke?

does having it closer to the hub make it less accurate? *i wrote something dumb here and deleted it *

just wondered?
Crafted in Italy apparantly

Comments

  • Mike67
    Mike67 Posts: 585
    ????? :D
    No the centre of the wheel goes around just as often as the outside if you think about it, unless you've some new invention that I've not heard of.

    The relative speed will be different for a fixed point on the rim (faster) as opposed to the middle (slower) so you could argue that the sensor has more time to pick up the magnet if it's nearer the middle.
    At the end of the day I don't think it makes much difference as long the magnet passes close enough to the sensor to give a good strong signal.
    Mike B

    Cannondale CAAD9
    Kinesis Pro 5 cross bike
    Lots of bits
  • acidstrato
    acidstrato Posts: 945
    haha I'm a twat

    thanks for that, not sure what i was thinking tbh, must have got too much sun on the bike lately

    that means i really was going that fast on the bike 8)
    Crafted in Italy apparantly
  • sungod
    sungod Posts: 16,853
    i tend to put mine closer to the hub than the rim, and opposite the valve

    the further out it is towards the rim, the more chance it'll affect balance, but unless it's a heavy magnet and the wheels are very light it probably won't make much difference in practice
    my bike - faster than god's and twice as shiny
  • acidstrato
    acidstrato Posts: 945
    well the reason i started thinking about it was because i only have a few cm to play with when positioning my GSC 10 sensor as the cadence magnet has to sit flat on the inside of my left crank arm but my tiagra crank arm is only flat at the end by the pedals thread.

    because of that the wheel magnet sat around the middle of the spoke. I dunno why but I figured it had to be at the top of the spoke. and then when out riding my speed just seemed abit to high for what my gut told me
    Crafted in Italy apparantly
  • sungod
    sungod Posts: 16,853
    ah, gsc10

    fwiw i lost the crank magnet, the nylon ties that garmin supplied weren't so good, and the sticky pad on the magnet couldn't take the weather, so one day my foot must have caught the tie and no more magnet, i replaced with two chunkier ties and another magnet

    best/neatest is probably to get a neodymium magnet and epoxy it to the crank
    my bike - faster than god's and twice as shiny
  • JohnnyAllez
    JohnnyAllez Posts: 785
    If you get a small rare earth magnet (strong type, around 8mm diameter and 3mm thick) and just put it on the end of the pedal spindle (where it pokes through the crank arm) it`ll stay attached by magnetism, no ties needed, and the GSC10 will pick it up from a greater distance than usual, due to the stronger magnetic force. They are available from various places for peanuts, including Ebay. :)
    Jens says "Shut up legs !! "

    Specialized S-Works SaxoBank SL4 Tarmac Di2
  • acidstrato
    acidstrato Posts: 945
    i've knocked it off a couple times too, but luckily seen it drop. got me thinking how much to replace it though, first result i got on google was 20quid for both magnets and a cable tie! :shock:

    nice tip JohnnyAllez tho will bear it in mind!
    Crafted in Italy apparantly
  • magoo289
    magoo289 Posts: 223
    I had the same problem. Turned the magnet upside down and pulled the ties as hard as I could. I don't have much of a margin to play with in regards positioning the sensor on the chainstay either due to curvature, its nearly on top of the cranks! I continuously check all 3 before, after and at cake stops.
  • yenrod
    yenrod Posts: 135
    Earth Magnet = Aint a 'Magnet' a 'magnet' or whatever; like Im not a scientist or such like BUT a magnet is just a magnet - weres this earth thing came in ?????

    Mr Thicko ;)
    [;)] 'tuono nel mio cuore...[:)]
  • SpiCan
    SpiCan Posts: 31

    Time VXS, Spi Roubaix Elite, Cannondale Caffeine F2,
    S Works Stumpjumper fsr, Dahon folding.
  • Dmak
    Dmak Posts: 445
    I put mine close to the hub but it gave duff readings. Told me I was doing 18-20mph up a 10% grind! It was too far from the computer. I've opted for halfway up the fork. Too far from the centre and you may notice the wheel wobbling from the weight of the magnet.
  • pete.whelan
    pete.whelan Posts: 788
    wireless speedo sensors work best at the top of the fork (less distance to the receiver)
    Recipe: shave legs sparingly, rub in embrocation and drizzle with freshly squeezed baby oil.
  • redvee
    redvee Posts: 11,922
    sungod wrote:
    best/neatest is probably to get a neodymium magnet and epoxy it to the crank

    Mine are stuck to the pedal shaft with magic fairy dust which explains why I paid £3 for 10 of them from Amazon. Any size from 3mm thick upto 12mm diameter will fit on the back of the pedal shaft for GSC10s
    I've added a signature to prove it is still possible.
  • T-Rekster
    T-Rekster Posts: 110
    If you get a small rare earth magnet (strong type, around 8mm diameter and 3mm thick) and just put it on the end of the pedal spindle (where it pokes through the crank arm) it`ll stay attached by magnetism, no ties needed, and the GSC10 will pick it up from a greater distance than usual, due to the stronger magnetic force. They are available from various places for peanuts, including Ebay. :)

    Now thats a valuable, insightful, beneficial, cheap & simple tip........top of the class sir!
  • pete.whelan
    pete.whelan Posts: 788
    If you get a small rare earth magnet (strong type, around 8mm diameter and 3mm thick) and just put it on the end of the pedal spindle (where it pokes through the crank arm) it`ll stay attached by magnetism, no ties needed, and the GSC10 will pick it up from a greater distance than usual, due to the stronger magnetic force. They are available from various places for peanuts, including Ebay. :)

    Great idea unless you have pedals with titanium spindles
    Recipe: shave legs sparingly, rub in embrocation and drizzle with freshly squeezed baby oil.
  • JohnnyAllez
    JohnnyAllez Posts: 785
    Bit of glue or silicone then Pete :wink:
    Jens says "Shut up legs !! "

    Specialized S-Works SaxoBank SL4 Tarmac Di2