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Bridging computer sensor gaps

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Bridging computer sensor gaps

Old 04-07-09, 05:54 PM
  #1  
Gil Elvgren
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Bridging computer sensor gaps

I am attempt to install a Cateye Astrale 8 wired computer with Cadence on a Specialized Globe City City 6 ING 8.

Cateye manuals says that Magnet and Sensor gap should be no wider than 5mm - approx. 3/16".

The gap between the left rear chainstay and spoke is approx. 1 1/2". The gap between the sensor and spoke magnet is 1/2". What can I use to extend the sensor closer to the spoke magnet to get it under 3/16".

The same gap of 1/2" is between the left rear chainstay and the left pedal crank. What can I use to move the magnet on the crank to get it under 3/16".

Thanks, Gil
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Old 04-07-09, 06:23 PM
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Move the wheel sensor further out on the chainstay (closer to the hub) and the crank sensor closer to the end of the crank arm.
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Old 04-07-09, 06:32 PM
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A different type of wheel magnet may help. If you are using one of theose flat plastic types, get a metal "button" type with a set screw in the back. They stick out further.

I have an Astrale mounted on my trainer bike. The magnet ( a button-type) is mounted right at the third spoke crossing about 1/4 of the way from the hub to the rim. The pickup coil is fastened to the chainstay pointed toward the rear of the bike and rotated in a bit to get the proper gap. I have no problems getting a strong reading
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Old 04-07-09, 11:12 PM
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I have a similar situation on my rain commuter (a circa 1990 Hard Rock). Because of how the chainstays are shaped, even at the nearest there's a wide gap between the stays and the spokes. My solution was to take a piece of an old tube (a fairly long piece, since I need more than half an inch of extra circumference) and wrap it around the chainstay as a spacer, then zip-tie the sensor to that. It has worked well for a few thousand miles.
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Old 04-08-09, 02:35 PM
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But it should usually be possible to move the magnet toward the hub (perhaps toward the rim) and find a spot where it can be close enough to the sensor, but there could be unusual cases where it can't be done, I suppose.

I had this problem with my cadence sensor. I zip-tied a strip of wood (maybe 3/8" thick) to the chain stay to shim the sensor out so it was close enough to the magnet on the crank. I used a little piece of cedar, which is easy to work with, and doesn't mind getting wet (and it's light, if that matters). I carved the back side so it was concave, to conform to the shape of the chain stay, and carved the front to match the concave back of the sensor. A strip of inner tube between the wood and the chain stay keeps it all from slipping around. Actually, if I hadn't been in a rush, I'd have soaked the cedar in warm water for a while, and it would have just bent to shape when I cinched down the zip ties (this is why wooden canoes are made of cedar: it's easy to bend). Not everyone has scraps of cedar lying around though, admittedly. Some kinds of wood wouldn't hold up well enough, probably. Cedar, maple, cherry, and ash would be good. Pine would be bad, probably.

But HillRider's suggestion to use inner tube (perhaps several thicknesses, if needed) seems like a good one, as well--much simpler than fiddling with bits of wood, I guess. Why didn't I do it that way? Maybe because I felt like fiddling with bits of wood.

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Old 04-08-09, 03:06 PM
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I took a wired bike computer and moved the speed sensor to the back wheel for use on my trainer over the winter. The sensor did not want to reach the magnet. I slit and tie-wrapped a piece of pneumatic hose over the chainstay and attached the sensor to that. It spaced it out about 3/8 of an inch closer to the spokes which was all I needed.
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Old 04-08-09, 03:26 PM
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I used some cut rubber grommets that I got at the hardware store under my sensor before applying the zip ties.
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Old 04-08-09, 04:01 PM
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You may also try sticking a rare earth magnet to the existing magnet.

It will help bridge the gap as well as increase the reading.
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