Speedometer question

[warezaholic]

I am placing a speedometer on the front wheel spoke at the rim and wonder about the max distance the sensor can be to work properly. My bike is a 26" Schwinn Meridian and the fork is about 2 1/2" from the magnet and the only close spot is on the welded break mount and has minimal surface area for mounting use! If the fork surface is too great a distance then my only other thought is to rig some form of spacer for the sensor between the fork and magnet...

Any input is welcome and appreciated.

 

[amberwolf]

Assuming hte magnet is on the spokes, then if you put the magnet close to the hub it'll be closer to the fork, most likely, and work easier without fiddlign with spacers.

 

[d8veh]

You can use a spacer, which is nearly always necessary on the back wheel. If that's still not enough, you can add a strong magnet to the one you have. The stronger the magnet, the bigger the gap can be. Look on Ebay for Neodymium (NdFeB) magnets about 8mm x 2mm. Grade N52 is the strongest.

 

[amberwolf]

BTW, it's sometimes actually better to use :"weaker" ceramic magnets for "filling air gaps" because their field is not held as closely to them as the "stronger" neodymium magnets.

Depends on the magnet and it's field orientation, too, some magnets have poles out the faces and some out the ends, some out the edges, etc.

 

[warezaholic]

Closer to the hub sounds good thanks, I first thought next to the rim because of centrifugal force would want to keep it there, but a dab of silicon will likely work!

The fork design on my bike is very large around and an axle mount welded on inner sides, making a greater distance from the rim than most other front forks.

 

[warezaholic]

Closer to the hub sounds good thanks, I first thought next to the rim because of centrifugal force would want to keep it there, but a dab of silicon will likely work!

The fork design on my bike is very large around and an axle mount welded on inner sides, making a greater distance from the rim than most other front forks.

 

[dogman dan]

Use a spacer.

My favorite spacer is made from a piece of foam floor mat. Or any other high density foam. It's soft, grabs well on the round fork, and by tightening the zip tie, you can crunch it down to exactly the right distance to just miss hitting your magnet.

Other things could work nearly as well, like a small piece of stiff 3/8" rubber hose. If you use a too large spacer, just rotate it away till you have the right distance to the magnet. It won't care about the angle, just the distance.

 

[warezaholic]

As a spacer, I was considering several layers of mounting tape as it already is sticky on both sides. M

 

[warezaholic]

It had occurred to me that the magnet and sensor would probably have to be at the rim for calibration purposes so it can be fixed at the 26" wheel size setting to get all correct readings!

 

[amberwolf]

Nope, it makes zero difference where it is. The number of rotations is exactly the same so it still measures speed the same.

 

[dogman dan]

Right, it just counts rotations. Double side foam tape a good idea for a spacer. But anything can work, even a small chunk of wood.

 

[warezaholic]

I was able to magnify the instructions enough be visible to my old eyes and it says "Max distance should be 1/4 inch"

 

[Voltron]

A 1/4" from the magnet the the sensor...not from the rim. It is just counting rotations...And you tell it the wheel size at the head unit so it knows how far each rotation goes. Also by getting away from the rim, the gate time on the sensor goes up as the magnet is passing it slower so the signal is nice and solid.