What size rare earth magnet do I need for a PD9000 pedal

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jspaceman
Posts: 236
Joined: Thu Sep 13, 2012 11:25 pm
Location: Ontario, Canada
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by jspaceman

I want to replace the cadence magnet on my crank arm with one of those disc or ring rare earth magnets that fit onto the back of the pedal spindle. What size do I need? Reading around the internet I see 8mm x 3mm, others say 1/2 inch x 1/8 inch, others say 1/3inch x 1/4 inch. Which is an ideal size for a good fit?

by Weenie


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Geoff
Posts: 5395
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

It almost doesn't matter. You can get-away with a really tiny magnet and still trip the reed switch (which is all you care about). Actually, you don't want a 'good fit' that completely seals-up the back of the pedal spindle, as it is easier to take the pedal off if you don't have to fight a rare earth magnet to get to it. I run SRM, but on my wife's bike, I have installed the smallest possible magnet. It fits on the edge of the pedal spindle and leaves the entire Allen key socket clear for maintenance.

Here is the place I get them cheap: http://www.leevalley.com/en/hardware/pa ... 42348&ap=1

The smallest size is all you need...

bluesea
Posts: 102
Joined: Sun Dec 27, 2009 10:55 pm
Location: Honolulu

by bluesea

Its not the pedal, its the crank arm that matters. Ideally a diameter that fits very *slightly* into the pedal threads so the magnet holds but is easy to remove.

I use 9/16" x 1/8" on Campy cranks. 1/2" would be more secure, but I haven't had any problems so....

jspaceman
Posts: 236
Joined: Thu Sep 13, 2012 11:25 pm
Location: Ontario, Canada
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by jspaceman

Lee Valley, forgot about them.

I'm thinking either the 1/2" by 1/8" or 3/8" by 1/8" version of these.

by Weenie


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Geoff
Posts: 5395
Joined: Sat Dec 13, 2003 2:25 am
Location: Canada

by Geoff

1/4" is more than enough! A 1/2" rare earth magnet is so strong you'll have junk sticking onto the back of it! There is no need for that much power just to flick a reed switch.

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