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  1. #1
    Join Date
    Apr 2011
    Posts
    117

    Question Help - Cadence Counter Crank Magnet

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    Hi all - my first post here. I have a question, and suspect it's been addressed and I am not looking in the right place. I have a Garmin Edge 305 with cadence counter. Lost the cadence magnet, but have ordered a new one. The problem I am having is that the crank arms on my bike are hollowed out/curved on the inside, and as a result, I haven't been able to mount the magnet close enough for it to be read by the cadence counter. It also doesn't fit tightly, which is why it got lost in the first place. Any suggestions? I've been reading quite a few of the posts on saddles and finding them very helpful. Thank you for all the information.

  2. #2
    Join Date
    Apr 2006
    Location
    where the wind comes sweeping down the plain
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    5,251
    I have the same problem, actually! When I had my other bike, it didn't have the hollowed out cranks on the inside and it wasn't a problem. When I built this bike, I didn't even think of that being an issue... until I went to attach the magnet. Doh!
    I don't know a solution. I thought about putting a piece of hard foam on the inside to take up the hollow place and zip-tie'ing it in place. Although I'm finding I don't even miss it (not like I thought I would).

    I'm sure someone will have a good suggestion!
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  3. #3
    Join Date
    Jul 2008
    Location
    Chicago suburbs
    Posts
    1,222
    I have a Garmin Edge 500. My crank (FSA SLK Carbon) also has curved arms. The crank magnet that came with my 500, has an adhesive backing to it helping it stick to the crank arm. Once I figured out where I wanted to position it, I peeled off the tape and stuck it on then secured it with the included zip tie. Mine seems to be staying put, although it has only been about 3 weeks since I put it on...so we'll see. If your magnet didn't come with an adhesive backing, then I suggest some double-sided tape to stick on the backside of the magnet to help adhere it to the crank arm. I also positioned my magnet closest to the pedal, which also happens to be the flattest part of the arm...so that may help too.
    2012 Seven Axiom SL - Specialized Ruby SL 155

  4. #4
    Join Date
    Aug 2006
    Location
    Melbourne Oz
    Posts
    174
    I use a small rare earth magnet which fits over the crank key hole. Couple of dollars; no sticky, definitely no zip tie!

  5. #5
    Join Date
    Feb 2010
    Location
    Taylor, MI
    Posts
    220
    Not particularly attractive, but electrical tape works to hold the magnet and it still works. The tape comes in assorted colors..

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  6. #6
    Join Date
    May 2010
    Location
    New Hampshire
    Posts
    87
    I have the Garmin 500 with the cadence and my magnet stays on but I can't for the life of me get it to actually read.
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  7. #7
    Join Date
    Mar 2008
    Posts
    2,704
    In the past, I've used some "poster putty" to fill up that gap before zip tying the magnet in place. Whenver possible, I use Oz's suggestion.

  8. #8
    Join Date
    Apr 2011
    Posts
    117
    Lots of good ideas here, thank you. My magnet came with the sticky back, but it didn't stick and even near the pedal end, it was too recessed to be read. I have read about the rare earth magnet and that would be a consideration as well and as several pointed out, it would look better without the zip tie. I have also thought about some kind of putty or something to fill the hollow before attaching the cadence magnet. What I was wondering about that, is if I would also need to put putty in the corresponding spot on the other crank, so as not to create some kind of imbalance that would cause wear and tear? (I'm kind of thinking like when wheels are out of balance - perhaps I am overthinking this.)

  9. #9
    Join Date
    Nov 2005
    Posts
    98
    Quote Originally Posted by goride View Post
    I have also thought about some kind of putty or something to fill the hollow before attaching the cadence magnet.
    Seems like some kind of epoxy putty would be great for this.



    Quote Originally Posted by goride View Post
    What I was wondering about that, is if I would also need to put putty in the corresponding spot on the other crank, so as not to create some kind of imbalance that would cause wear and tear? (I'm kind of thinking like when wheels are out of balance - perhaps I am overthinking this.)
    Definitely overthinking. No need for a counterbalance.

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  10. #10
    Join Date
    Jul 2008
    Location
    Chicago suburbs
    Posts
    1,222
    Quote Originally Posted by feral1 View Post
    I have the Garmin 500 with the cadence and my magnet stays on but I can't for the life of me get it to actually read.
    Are you making sure that the magnet lines up exactly with the "line" on the sensor? There is also a tiny light on the sensor that will flash green when it picks up a signal from the cadence magnet, and red when it picks up a signal from the speed magnet. Are the batteries in the sensor fresh? That's all I can think of at the moment.
    2012 Seven Axiom SL - Specialized Ruby SL 155

  11. #11
    Join Date
    Apr 2011
    Posts
    117
    Got it! I ordered a couple of small Cateye magnets which someone mentioned in another area of the TE forum. I like them better than the style of magnet that came with my Garmin because the zip type passes through the magnet case instead of over the top of the case. The magnet is sticky backed, but still didn't stay attached to the crank. I used the zip tie which came with it, but with the hollow back, and the crank being straight and not tapered, I still found it sliding back and forth on the crank. I took a couple small pieces of dark gray water pipe insulation foam, and shoved them between the zip tie and the back of the crank. Problem solved.

    I did have a "duh!" moment on yesterday's ride. I looked down and saw that my cadence was not registering, then I realized I was "coasting." Oops.

  12. #12
    Join Date
    Apr 2006
    Posts
    1,372
    Quote Originally Posted by oz rider View Post
    I use a small rare earth magnet which fits over the crank key hole. Couple of dollars; no sticky, definitely no zip tie!
    +1
    me, too, since +1 isn't long enough.
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