The strength of neodymium magnets

For a long time I have been wondering about the strength of neodymium magnets. When I have been out on a magnet fishing trip, my strong magnets with a force of 110 kg ~242 lbs have had many troubles lifting things from the bottom of the lakes which have had a weight of a lot less than 110 kgs. I have many times lost several bicycles 20 times and only caught it in the end because the magnet got stuck in the wheel or something else. This is weird right, because a bike should weigh about 15 kgs or less? And in the water it should weigh even less.

The real strength of neodymium magnets is practically a lot less than the given 110 kgs. Of course if you have a new, clean magnet, a flat surface without algae and so on, the magnet might be able to carry 110 kgs ~ 242 lbs. Acutally I once tested my magnet when it was all new and clean. I put it underneath a stair case where the bottom of each step was made from iron. From here, my 90 kgs could hang in the magnet without the magnet letting go of the staircase.

So what can impact the strength of neodymium magnets?
Several things can have an impact of the strength of your neodymium magnets.
​

• If your magnet is old as mine, there might be a lot of gravel and small stones on the bottom of the magnet. This has a directly impact on how well the magnet can hold on to the objects which it is trying to catch. The time when we caught the safe, one of two exactly identical magnets kept losing its grip on the safe. When we finally pulled the safe on shore, I noticed it was because there was a nail on the magnet which prevented the magnet from getting properly stuck to the safe.
  
  
• If the surface of where the magnet is stuck, isn't completely flat. An example could be bicycles as previously mentioned. Most bicycles have round surfaces, which unfortunately results in a hard time catching them.
  ​
• Gunk on the items you catch. If you get your magnet stuck to something which has been in the water for ages, the chances of it being full of gunk is quite big. This gunk makes it easier for the magnet to slide of and loosen its grip on the item.

So in the end, if the conditions are perfect for the magnet, the real force of the magnet is the same as given from the factory. But as soon as you take your magnet out you will see that the real strength of neodymium magnets is limited by the nature. Remember to clean your magnet before you throw it in the water, it will increase your catch rate!