I've just started my mechanical engineering course too

Quote Originally Posted by ekslut
Spring Pre-Load - Compressing a spring in advance of adding a load.
Example: Using a 100 pound linear-rate spring, preloaded one-quarter inch, would take twenty-five pounds of force before it would further compress. In effect the spring will not compress until 26 pounds of force were applied. The spring in this instance will only move one-quarter inch when 50 pounds of force were applied, as opposed to the half inch the spring would have normally moved.
I think what 'Muzz' was saying is correct (If I am reading it all correctly). If the spring is 100mm with a spring rate of 10kg/mm and is already pre-loaded 20mm then it will need over 200kg of force to get it to compress anymore. The actual spring rate has not changed, as it will stay to the same rate; @400kg of force it will compress 40mm, which is only another 20mm over what it is pre-loaded at.

Therefore the more its preload it means that the spring will need more force applied to it before it starts to work as if it didn't have any pre-load. Meaning this is why it 'feels' like it is stiffer.

This has turned into a very intresting thread