They say 90lbs per cross rail static.
8 rails standard = 720lbs
And of course if you have no sunroof you can add 2 more cross rails to fill the gap.
If I understand this correctly, if one cross rail supports 90lbs I'd break a cross rail by stepping on it since I weigh over 200lbs. Somehow my weight would need to be spread over 3 rails to support me.
Also are there ladders for these?