Hi!! I'm curious about the dynamic and static weight capacity of the stock roof racks on my 1999 4Runner. I want to put a rooftop tent on there (weighing 100lbs). Then 2 people sleeping in it = 275lbs.

 

Check the owners manual... it's in there somewhere IIRC. I would look but mine got lost 5-yrs ago. I think it was a 150lb limit but I won't swear to it.

 

I was looking at a stock cross bar the other day - it said 165 lbs 'evenly distributed'.

I think that's more the limitation of those crossbars themselves (with their plastic ends/feet) than the rails and roof itself.

 

Exactly right on the cross-bars with load-bearing plastic parts. I do not trust those.
Safest is to use custom roof rack with metal mounts.
OR after-market cross-bars and fabricate your own mount using a solid material such that the load will be on metal crossbar and on solid mount.
Example:
Take solid block of delrin or aluminum, drill clearance holes, use t-nuts / t-bolts to mount block on factory rail like this:






Mount after-market cross bar on solid block with something like this...



Next safest solution is aftermarket cross bars with metal towers on the stock rails of the 3rd-gen.