Calculating Magnetic Strength.
 

Does anyone know a simple way to calculate the strength of the magnetic discs I have in my tank bag?

Basically I want to buy more magnetic discs to adapt a tailpack, but I'd like to make sure they are strong enough so it stays put, but not so strong that I can't get it off.

Any help would be great.

Re: Calculating Magnetic Strength.
 

Can't help with any calculations, but I can suggest that as magnets are very short range, you can pad out the magnet until it's as powerful as you want. Just add/remove layers of foam or paper or cardboard or whatever as required. I've never had a magnet so powerful it was impossible to remove - even huge speaker magnets or uber powerful hard disk magnets come off with enough effort.

I'm guessing you'll want fairly strong ones and with a large surface area. Small magnets are the worst because you can't get any leverage on them.

Re: Calculating Magnetic Strength.
 

A really basic and simple way would be to stick the bag to something metal whilst upside down (taking the tank off the bike and using that would be the most accurate but possibly a little extreme) and then keep adding weight to the bag until it comes unstuck. Then weigh the bag and divide by the number of magnets. Result is how much each magnet sticks.

Alternatively have you got one of those portable scales with a hook on we use for weighing our bags when we go on holiday? If so put the bag on the bike, attach hook to appropriate location and pull it off.

Re: Calculating Magnetic Strength.
 

Stick one each side and see how much it hurts.

Re: Calculating Magnetic Strength.
 

due to there being fabric between the magnet and the metal it would have to be blooody strong magnets not to be able to lift them off. i very much doubt you could buy a strong enough magnet cheaply enough that it would be permanent.

Re: Calculating Magnetic Strength.
 

This might give you an idea on the pull strength of magnets.

https://www.amazingmagnets.com/sf-disc-magnets.aspx

Re: Calculating Magnetic Strength.
 

Just install an electromagnet. Then it will only come off when you want it to!





http://e-magnetsuk.com/magnet_produc...romagnets.aspx

Re: Calculating Magnetic Strength.
 

Use Neodymium magnets, which are much more powerful than the usual ones.

I've bought them as crank sensors for the Garmin cadence sensor, tiny and require no glue or sticky pads to attach to the pedal spindle, just magnetism. Its magic!

Loads of shapes and sizes here

http://www.first4magnets.com/rectang...ets-c35#:page2

Or speak to this guy

http://i.annihil.us/u/prod/marvel/i/...background.jpg