I think it was in the Bendpac manual that I saw cautionary notes on how to proper load a four post lift. Basically, they say don’t try to lift a 9900 lb short wheelbase forklift. On a 10k four post lift.
The ratings on these lifts assume some pre established wheelbase and roughly uniform weight distribution among the four posts. The capacity is de rated the farther from the posts the load is.
I use the jacking plate or air jacks to lift the vehicle either from the axles or from contact points immediately behind the front wheels or in front of the rear wheels, and see no obvious ramp deflection on my Advantage lifts. Logically that makes sense, as I am, in one case not changing the ramp loading at all, and in the other case, only changing the moment arm by about a foot. If I tried lifting from the midpoint of the wheelbase, I am changing the ramp loading significantly by changing the lever arm moment acting upon the ramps. I would derate in that event, I.e. not try to lift a 12k lb truck on a 12k lift With an air jack in the center of the ramp length.
