Originally Posted by Jim34RL
How does the mass change from being inside the camper and then being extended for the slide? If you do a free body diagram of the mass involved you would see there is no change in the total mass of the unit. Now the bending moment is different on the frame but not on the stabilizer legs and jacks. you still have the same downward component on the legs and stabilizer jacks.
Now when setting up a trailer/motorhome on a soft site or hard site consisting of gravel/concert pad; I would always recommend pads 1x12x12 plastic or wood blocks of similar size under the stabilizer and jack legs. This way you will spread the downward component (load) of the mass in the trailer over a larger area.
I use two 4X4x12 inch wooden blocks under each 8" round pad on my unit when setting up. I have seen the blocks sink a little bit but the load is spread over a larger area. I also place the trailer tires on two 2X8X6' long boards when I am on dirt or grass. I have never seen the blocks sink any farther when the slides are extended.
The mass doesn't change, Just the amount of force where the mass is supported when the slides are extended. (leverage point)
When the slides are all in and the stabilizers are all extended, the mass is pretty evenly supported by all 4 stabilizers because the mass in pretty much centered. When you extend the slides (again we are talking mostly about a rig with just slides on one side) the force applied to the stabilizers on the slide side increases and the force on the stabilizers on the non-slide side is decreased.
Think of it this way... climb in a shopping cart/buggy and sit in the basket.
All your weight is supported evenly on the four wheels and you don't tip over.
Now... climb back out and hang off one side of the cart and see what happens. Same mass, different leverage point.