How has this post devolved to 4 BICYCLES.on a ROOF???
Because it got serially hijacked? Do I win a point?
Tbe original question and answer were simple. All the rest is personal preference statements...it's all good. People are (probably rightly so) very opinionated about what exactly is "safe towing/hauling".
Here's a good resource on understanding tongue loading as it affects sway: hope it helps someone
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1029.4946&rep=rep1&type=pdf
A careful reading of the graphs shows that speed is the most important variable in stability.
If you fall in the camp of being more concerned that "it'll rip the unibody to shreds", then you have some more homework to do. Some unibodies are strong. Some aren't. It's a very complex topic actually. Unless you run your own FEA analysis of your car; I'd recommend to stick to manufacturer's recommendations.--Caveat: most manufacturers list much higher permissible maximum tongue loadings in the European market than in NA market, even for EXACTLY identical vehicles. This is because they want to push higher margin SUV and pickemup sales in the North American market, where buyers have largely bought into the propaganda that "you really need an F250 or 2500-series truck to tow 2500 lbs".
Hint: you don't. Just follow the Euro guidelines: never tow more than 85% of the TV's mass. Slow way down (I see you 5th wheelers doing 95 mph, towing a 16,000 lb 36 footer on I-10! You should be in jail, IMO. Most mid-size and even a lot of compact class passenger cars can handle 7%-9% of the towing vehicle's mass to be loaded onto the tongue. (Another hint): it's because when trailer tongue loads exceed 7% of TRAILER MASS at legally permissible speeds, and observing the 85% rule, that's how the numbers shake out--and there's almost NO possibility of sway (self damping always present). That's what the engineers are targeting.