The maximum capacity of your roof rack system will be dependent on the lowest rated part of the system.
Weight limit on roof rack.
For tents weighing more than 165 lbs 75kg the maximum weight capacity of the rack and vehicle must be equal to or greater than the tent weight.
We installed a powerful 4 4 full length steel cage roof rack on a mates patrol a few years back and weighed it at at around 60kg.
Your vehicle and roof must have a minimum driving dynamic weight capacity of of 165 lbs 75 kg.
The safety factor is 1 5 to 2 depending on the roof rack and fixture style you can find the safety factor in the roof rack instructions.
Refer to rooftop tent and rack.
So if you have a roof mounted cargo box that has a weight capacity of 150 lbs roof rack crossbars that are rated at 200 lbs and these are on a roof rated at 100 lbs then you cannot load more than 100 lbs.
To calculate the off road load rating divide the load rating by the safety factor then subtract the weight of the racks this will tell you the safe off road cargo rating for your vehicle.
When parked the additional weight of humans and gear in a rooftop tent can be much higher.
Total weight 40 2 lbs 165 lbs limit 40 2 lbs rack accessories 124 8 lbs available load capacity note insure you include the weight of any other accessories ski bike boat mounts attached to the bars.
Something that is often overlooked is the weight of your roof rack itself.