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Old 12-28-04, 11:23 AM   #1
timhines
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Installing a Cyclocomputer on a road bike

I hope I posted this in the right forum.

I'm new to cycling. I bought an Ascent wireless computer for my new road bike. I have a question though.

When I install the little magnet on the spokes, does it matter where I put the magnet? I'm mounting the transceive to the front post and have the little magnet a couple inches from the tire.

Any help is GREATLY appreciated (pics are also nice).

Tim
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Old 12-28-04, 01:00 PM   #2
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It matters how close the reciever(on the handlebars) is to the sensor on the fork so I would mount it as high up as possible.

However it also matters how close the magnet is to the sensor. On my cateye wireless it says that the magnet should pass no more than 5mm away from the sensor.

You also have to program the computer to the tire/wheel size. Usually in the manual it has a size chart for tiresize x wheel size(i.e 700cx23mm = 2096mm circumference)

sooooo... to answer the question you actually asked, yes it matters where you put the magnet on the wheel.

oh, BTW, the magnet has to pass right by the sensor. Usually there is a line on the sensor telling you where the magnet has to pass in order to work.
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Old 12-28-04, 01:02 PM   #3
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I'm not really sure what you're asking, but it doesn't matter where you install the magnet along the spoke length, as long as the reciever is at the same height on the forks, and when the magnet passes it, they are close together (check in the manual for exactly how close). If you're asking whether it makes a difference whether you put the manget near the tyre or the hub, no it doesn't
Hope this helps a bit
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Old 12-28-04, 01:08 PM   #4
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Thanks guys. I do have the magnet passing the transceiver with about a penny's width inbetween the two.

However the magnet is a couple inches form the tire.

I just thought that the magnet would need to be as close to the tire as possible to represent the tire size.

I'm taking a ride tomorrow and will measure the first mile to be sure it's accurate. If it works, I will call it magic. If it doesn't work.....you'll hear from me soon.
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Old 12-28-04, 01:15 PM   #5
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Yep, clearance matters but not where on the spoke.
Every point on the spoke is on the same number of degrees for a given rotation.
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Old 12-28-04, 01:37 PM   #6
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the magnet should also be on the opposite side of the wheel to the valve for wheel balancing reasons
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Old 12-28-04, 01:43 PM   #7
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Quote:
Originally Posted by timhines
Thanks guys. I do have the magnet passing the transceiver with about a penny's width inbetween the two.

However the magnet is a couple inches form the tire.

I just thought that the magnet would need to be as close to the tire as possible to represent the tire size.

I'm taking a ride tomorrow and will measure the first mile to be sure it's accurate. If it works, I will call it magic. If it doesn't work.....you'll hear from me soon.

Did you program the computer for the wheel size? Thats very important...
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Old 12-28-04, 01:45 PM   #8
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yes, a 700x23c tire.

EDIT:
2105mm programmed into the cyclocomp
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Old 12-28-04, 01:50 PM   #9
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Get the mag and reciever as close to the hub as possible (and still have the computer picking up the signal) to reduce the inertial impact on your wheel.
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Old 12-28-04, 03:14 PM   #10
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Not to mention the road junk on sensor.
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Old 12-28-04, 04:07 PM   #11
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Each time the magnet passes the sensor, it registers one revolution. As you have allready put in the circumference of your tyre, it wouldnt matter where along the spokes the magnet is set up, as the circumference of your wheel registered in the computer is the same. Near the hub makes sense to reduce rotational weight, and keep dust and dirt off it, but sometimes it's not possible if the spokes are too far away from the fork. Doesn't really matter though. I actually run mine close to the tyre, so i have less cable running over my bike, looks tidyier.
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Old 12-28-04, 04:47 PM   #12
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Quote:
Originally Posted by matheprat
Each time the magnet passes the sensor, it registers one revolution. As you have allready put in the circumference of your tyre, it wouldnt matter where along the spokes the magnet is set up, as the circumference of your wheel registered in the computer is the same. so i have less cable
Absolutely correct. The period of revolution is constant no matter where you are on the spoke. As far as where to mount the magnet, I have a Trek that says "3 to 6 in. from the hub" and I have a Vetta that says "~2 in. from the rim" - so, the point is that you should see what the manufacturer suggests in the user manual. Magnet sensors can be Hall effect devices (that are triggered by hysterisis), or, reed switches that act very much like a relay. Hall effect sensors are very sensitive and are good to sense a fast moving magnetic field (like out by the rim). Reed switches have to be given ample exposure (over time) and are better matched to a slow moving field. Wired sensors are usually reed switch and wireless are usually Hall effect (that's why wireless need the battery - to power the Hall effect sensor circuit). In any case, you should definitely consult the manufacturer's suggestions for mounting.

Last edited by cascade168; 12-28-04 at 04:59 PM.
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Old 12-28-04, 04:58 PM   #13
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Quote:
Originally Posted by timhines
When I install the little magnet on the spokes, does it matter where I put the magnet? I'm mounting the transceive to the front post and have the little magnet a couple inches from the tire.

Tim, here is a pointer to an Ascent computer owner's manual:

http://www.nashbar.com/tech/pdf_file...08FC_FINAL.pdf

I don't know if you have this exact model, but hopefully this will help. It does suggest where you place the sensor and magnet.
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