Help!! Where abouts on the spoke do I put the magnet for my bike computer?

[parklaneyido]

I have just seen a picture in this weeks cycling plus that has made me think I have set my bike computer up wrong. In the pic, they guy had his magnet right at the top of the spoke... Is how it's supposed to be done? I have placed my magnet about three inches from the top... I'm wondering if this means my computer is telling me I'm going faster than I actually am....

Should I get hold of a couple of cable ties and relocate the sensor and magnet?

 

[Oldlegs]

It doesnt matter where you put the sensor. The computer counts how many times the wheel rotates not how fast its going.

 

[ufkacbln]

There is a compromise.....

As the spoke nears the hub, it s closer to the fork.

The trick is to move the sensor and the magnet up and down until the optimum distance is reached

 

[dantheman]

my computer fell over itself, not counting all the rotations, and hence my mph reading was switching from, say, 20mph, then 10, then back to 20, so i put it in the centre, so the magnet is travelling at a slower speed, giving the sensor more time to detect it, it solved the problem..

 

[Tharg2007]

put it on the rims, if it sticks get some new wheels

 

[PaulB]

It doesnt matter where you put the sensor. The computer counts how many times the wheel rotates not how fast its going.

What he said. Regardless of where you put the sensor, the wheel rotates the same number of times so provided you've told the computer what the diameter is, no problem.

 

[jimboalee]

1/ The computer magnet is best placed in the V where centrifugal force pushes it closer into the V.
2/ The computer magnet should be close to the hub.

Dantheman is correct here.
The sensor detects the passage of the magnet every time the wheel goes round. This is how it computes distance per time using time to cover the circumference of the wheel.
If you place the magnet close to the rim, and the wheel takes 1 second to rotate, it takes 1 second to travel a greater distance than if the magnet were close to the hub and therefore has a greater velocity. It is a ratio of radii, assuming Pi is constant.
In other words, the magnet is flying round the larger radius and cruising round the smaller radius. Placing the magnet on the smaller radius gives the sensor more time to detect the magnet.

 

[parklaneyido]

thanks for your help peeps... I won't bother adjusting it all then... Good thing really as it's the best job I've made of a computer lol

 

[Danny]

Don't adjust it!

I recently moved my magnet and sensor to what I thought might be a better position, but did not leave enough slack in the wire, so when my handlebars next got turned fully to the left I snapped the wire from the computer to the sensor , which was an embarrassing and expensive mistake.

PS (and totally OT) I can't resist taking the opportunity to congratulate parklaneyiddo on the excellent start his team have had to the season.

 

[parklaneyido]

Don't adjust it!

I recently moved my magnet and sensor to what I thought might be a better position, but did not leave enough slack in the wire, so when my handlebars next got turned fully to the left I snapped the wire from the computer to the sensor , which was an embarrassing and expensive mistake.

PS (and totally OT) I can't resist taking the opportunity to congratulate parklaneyiddo on the excellent start his team have had to the season.

I've got a wireless computer so wouldnt have had that problem if I did adjust it... I'm not going to though...


Oi, I've getting enough stick about THFC as it is

 

[jimboalee]

I've got a Garmin. What is the magnet used for?

 

[Gary D]

I've got a Garmin. What is the magnet used for?

It fits on the rear wheel and works in conjunction with the GCS-10 Cadence Sensor. It will give you a speed reading if you lose satellite reception.

It can also be useful if you use a turbo trainer. Disable the satellite function, and it will give you a speed reading.

Gary.