I have looked in the manuals which only referred me to look at the GVWR , etc. weight limit plate on the cars . Nothing tells me what the roof , rack and crossbars can handle , weight loading-wise.

There should be a sticker somewhere in the upper door jamb or on the rails that says. If not there look in the upper jamb of the rear hatch.

The usual limit is about 150lbs, evenly distributed on the rails.