There has been a lot of discussion over the years about rated recovery points. Shiny plates with a SWL or WLL stamp are often taken to be safe for the rated capacity.
These plates are only as good as what they are attached to, and importantly how they are attached. You will struggle to find any information that rates the holes that are used for mounting most of these recovery plates. Just as important is the method of attachment. When designing plates to bolt together to take a load in shear, the friction of the joint is an important factor. The joint should be designed so that the bolts create a friction joint and don't just take a shear load as is the case for most recovery points. And using 'high tensile' bolts doesn't do away with the need to use them correctly. They are designed to be high tensile in tension, clamping a joint together. They are not designed specifically for shear loads as they are often used when attaching a recovery point. Anyway I could go on, but I'd love to see some science to the rating of recovery points.
The 'tie down points' as they are often called and which come on the vehicle from the factory are actually engineered by the manufacturer to take loads. Take a close look and you will see that they are not some flimsy bits of metal, not on the Prado anyway.
I decided to do some quick calcs on the 'tie down points'. If there are any welding experts please let me know if I got this wrong.
Each u-shaped 'tie down' is 16mm diameter and has 4 full circumference fillet welds holding it in place. That gives 5cm for each weld x 4 is a total of 20cm = 7.9inches of weld for the u shaped tie down. The fillet welds look to be about 8mm but lets round that down to 6mm (1/4inch) for safety. Rule of thumb says that 1/4 inch weld can hold 1t / inch (a conservative number backed by some complicated welding theory). So that gives a theoretical dynamic rating of 8t for each 'tie down point'. Let the flood gates open....
edit: And by my calcs the 16mm bar should be good for about 10t, so the welds should fail first.
These plates are only as good as what they are attached to, and importantly how they are attached. You will struggle to find any information that rates the holes that are used for mounting most of these recovery plates. Just as important is the method of attachment. When designing plates to bolt together to take a load in shear, the friction of the joint is an important factor. The joint should be designed so that the bolts create a friction joint and don't just take a shear load as is the case for most recovery points. And using 'high tensile' bolts doesn't do away with the need to use them correctly. They are designed to be high tensile in tension, clamping a joint together. They are not designed specifically for shear loads as they are often used when attaching a recovery point. Anyway I could go on, but I'd love to see some science to the rating of recovery points.
The 'tie down points' as they are often called and which come on the vehicle from the factory are actually engineered by the manufacturer to take loads. Take a close look and you will see that they are not some flimsy bits of metal, not on the Prado anyway.
I decided to do some quick calcs on the 'tie down points'. If there are any welding experts please let me know if I got this wrong.
Each u-shaped 'tie down' is 16mm diameter and has 4 full circumference fillet welds holding it in place. That gives 5cm for each weld x 4 is a total of 20cm = 7.9inches of weld for the u shaped tie down. The fillet welds look to be about 8mm but lets round that down to 6mm (1/4inch) for safety. Rule of thumb says that 1/4 inch weld can hold 1t / inch (a conservative number backed by some complicated welding theory). So that gives a theoretical dynamic rating of 8t for each 'tie down point'. Let the flood gates open....
edit: And by my calcs the 16mm bar should be good for about 10t, so the welds should fail first.
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