I have a pair of 16,000 lb Rhino ramps I drive my cars up when I change the oil. Because of stories of ramps and jacks failing, I like to use a stack of boards that I have in my garage, as a backup plan. I put them in between the two tires on each side. My question is—is there a given height that my stack of boards should go? Do I simply have to put my stacks high enough to allow me to have room, below the level of the boards, if the chassis falls? Or could the innards at the bottom of the car, drop lower than the frame itself, that is resting on the boards—in which case, I’d need to give myself a few extra inches of leeway here.