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Old 10-06-06, 01:04 AM   #1
Gotte
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bike computer question

I got a wireless bike computer from decathalon in UK, and it works fine. The only problem is that the instructions don;t specify how highut the magnet on the wheel, or the sensor on the fork. THere's a crude diagram that shows it roughly 2/3 up the fork (maybe, it's hardto tell), but I was talking to a guy who said he understood that sensors in genera should go at the centre of the fork.
Anyone know? I'm guessing it's critical, as if it's too high it'll go too fast, and too low it'll go too slow.
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Old 10-06-06, 06:07 AM   #2
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You can secure the sensor on the fork anywhere and it wont effect accuracy. But for the sake of arguement place it high up on the fork, in-line with the magnet on the spoke 2-3 inches from the rim. Make sure there is about 2mm clearance from the magnet and sensor.

Should do you good.
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Old 10-06-06, 08:06 AM   #3
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Whether you put it 1 mm from the hub or all the way out to the rim, it counts RPMs. Put it where ever you want. The inside of the wheel can't go more revolutions than the outside of the wheel or vise versa. It simply counts the revolutions and multiplies that by the wheel circumference which you input manually.
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Old 10-06-06, 09:38 AM   #4
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Ahhh, i see. Thanks for that.
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Old 10-06-06, 09:48 AM   #5
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Whether you put it 1 mm from the hub or all the way out to the rim, it counts RPMs. Put it where ever you want. The inside of the wheel can't go more revolutions than the outside of the wheel or vise versa. It simply counts the revolutions and multiplies that by the wheel circumference which you input manually.
Everyone knows this, but you also neglect to mention that the speed of the magnet going across the sensor is lower as you approach the hub which may matter.

Even though that's true here's what Sheldon says:

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With one-magnet cyclecomputers, you usually have a choice of several places on the wheel to attach the spoke magnet, depending on the spoke pattern of the wheel. Generally, it is best to mount the magnet as close in toward the hub as possible. The closer in you mount it, the more slowly it will pass by the sensor, giving the sensor's magnetic switch more time to respond. If the magnet is too far out, the computer may give erratic readings at higher speeds.
I always place mine near the hub.
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Old 10-06-06, 09:54 AM   #6
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I've found that the biggest problem in getting bike computers to function properly is getting the spacing between the wheel magnet and the pickup right. Usually (but not always) that works out better when the magnet is closer to the hub.
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Old 10-06-06, 11:12 AM   #7
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As close to the hub as possible is also good because it takes less effort to move rotational weight a shorter distance.

[granted, a wheel magnet doesn't weigh much, but it was my reasoning when i installed my cyclometer]
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Old 10-06-06, 03:27 PM   #8
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Everyone knows this, but you also neglect to mention that the speed of the magnet going across the sensor is lower as you approach the hub which may matter.

Apparently the OP didn't know this....that is why I said it. And the difference in speed from the hub to the rim is neglible considering you can be going anywhere from 4 mph to 70 mph and many thousands of rpms. If the darn thing can read it at 50 rpms or at 10,000 rpms you are just fine.
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Old 10-06-06, 07:05 PM   #9
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I'm just going to throw this out there in case anyone else ever has the problem I had with wireless. It was a cheapie, Axiom A10, but the problem probably could affect any wireless.

I commute to work and the spot I park my bike, the safe spot, is next to a alarm sensor. Evidently, the sensor would cause the wireless to pickup a signal. I could walk past the bike and the speedometer would be reading 56mph. Ruined my weekly averages. But, impressed my wife.LOL

I've since switched to a wired Cateye and the problem was eliminated. I actually preferred the Axiom, I could reset it daily, but maintain my weekly mileage count. A feature the Cateye doesn't have. I'm wishing now I would have bought the $19.99 Axiom A08.
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Old 10-06-06, 09:35 PM   #10
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For wireless, the distance from the sensor to the computer is meaningful - the closer it is, the better signal you get, and the less interference.
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Old 10-07-06, 08:22 PM   #11
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I had a wireless Sigma and got rid of it for a wired Cateye w/cadence with the speed sensor to the rear wheel. Wired is more reliable and accurate and you don't go through batteries like you do with the wireless. I have mine wired so nice you could barely notice the wire. I have it wrapped around my speed shift cable and it looks awesome. It looks like a solid black speed shift cable. Actually looks better.
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Old 10-08-06, 04:44 AM   #12
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Thanks for the input, chaps. Wireless is good for me because I can move it realtively eaisily from bike to bike when I change mount for any period of time.

But I might try a wired for the cheap MTB I've got hooked up to a trainer - winter's coming and I expect I'll be on more now.
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