OK. I did a simple test to see how much the pads compress under load. I placed two pads between two ground steel plates and measured the gap between the plates at .240". This is basically the pad thickness without a load on them. Then I started squeezing the plates together and measured the gap at various loads. Here is what I found. At 100# load, the gap had not changed appreciably. At 500# load, the gap was .235", a compression of .005" which is the thickness of two layers of newspaper. At 1000# load, the gap was .223", a compression of .017. At 1500# load, the gap was .205", a compression of .035".
Remember there are two pads in this test, so the load per pad is 1/2 of the total load. It seems unlikely that a typical truck would see 1000# per cross sill on a regular basis. Even a compression of .017" is probably absorbed readily by the structure of the bed.
Over time, the pads will likely take some kind of permanent set and change thickness just from having a constant load on them. I have no data on that. I just did this test to help you get an idea of the stiffness of the pads and their response to the load applied.
Also, we recommend you place the pads between the wood block and the frame, to avoid possible distortion of the bracket on the cross sill.
Let me know if you have questions
Mar-Ktech
