# Can I Make A Replacement Magnet Device For My Cycling Computer?



## bemmis (Sep 14, 2008)

I just found an specialized cycling comuter of mine but i can't find the magnet device that mounts to the spokes. Is there some way to make a replacement one out of a refigerator magnet or something? 

I know my lbs sells a replacement but I would rather save $8 and make my own. Would i need a special kind of magnet or a certain way of orienting it on the spokes?

thanks.


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## FatTireFred (Jan 31, 2005)

it's just a magnet


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## RichL87 (Sep 23, 2008)

From my understanding of magnetism and physics all the contraption consists of is a magnet (any small magnet that's strong enough) and a sensor that reads the pulses of electricity created by the magnetic field passing an inductor or a wire or something. Just strap a magnet on your spoke and see if it works.

-Rich L


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## tomk96 (Sep 24, 2007)

rare earth magnets work great


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## jupiterrn (Sep 22, 2006)

any magnet will do, just make it small and zipp tie it to a spoke.


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## skeedunt (Sep 10, 2008)

I have an old specialized computer that I don't use anymore (with the magnet), I'll mail it to you (the magnet) if you're in the u.s.


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## Dinosaur (Jan 29, 2004)

Any magnet will work..


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## C-40 (Feb 4, 2004)

*info...*

You can get a whole package of small magnets at Radio Shack, Home Depot or Ace hardware and probably any craft store.

You can't zip tie a magnet to a spoke, however. You'll need to glue or tape it in place. That's a lot easier with wide bladed aluminum spokes like Mavic Ksyriums use, than it is with thin round stainless steel spokes. With conventional spokes, I might break down and buy a magnet with the clamping screw. A few bucks in not worth much of my time.


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## MerlinAma (Oct 11, 2005)

I use Mavic flat spoke wheel magnets exclusively.

http://store.tri-sports.com/maflspwhma.html

They work on round spokes too.

Very aero and soooooooooooo cool!


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## Kuma601 (Jan 22, 2004)

The Cateye replacements are $4 typically. 

Those rare earth magnets are great...watch out for riders on steel bikes though.


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## Blue CheeseHead (Jul 14, 2008)

For a spoke, break down and buy one. A refrigerator maginet is not likely to be strong enough. You are going to spend a few bucks on a rare earth maginet. Just pony up a couple more bucks and get the right thing.


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## FatTireFred (Jan 31, 2005)

cateye will sell you a magnet for $2-3 and won't rape you on shipping... i.e., only charge postage = whatever a stamp is these days


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## JCavilia (Sep 12, 2005)

*close, but not QUITE right*



RichL87 said:


> From my understanding of magnetism and physics all the contraption consists of is a magnet (any small magnet that's strong enough) and a sensor that reads the pulses of electricity created by the magnetic field passing an inductor or a wire or something. Just strap a magnet on your spoke and see if it works.
> 
> -Rich L


You're right that any small magnet that's strong enough and passes close enough will operate the sensor. But the sensor in most (all?) bike computers is even simpler than you suppose. Rather than using induction, it's a simple reed switch -- a switch that's normally open, with one side of the switch being a thin springy steel wire. When the magnet gets close enough, it pulls on the spring, closing the switch. When the magnet moves away, the spring opens it up again. So you get a brief pulse of current, and the computer measures the time interval between successive pulses to calculate your speed.


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## Guest (Nov 1, 2008)

Rare earth magnets are very handy to have around, I find they make most cycling computers work a lot better.

Careful though if you use one of the Polar powermeters, because that system mounts on the drive side I have seen magnets that were strong enough to attract the chain as it goes by.


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