Minimum tongue weight, bordering on dangerous, is 10%.
Sorry but you are totally Wrong, That was the Norm in Australia until Vehicle Manufacturers Started Adding factory limits on the Tongue Ball or Hitch weight That 10 or 20% might be the case In the US if a person Drives an F-Series Ford or a Ram 2500 or Chevy that can gross out at over 20,000Lbs,
Vehicles in the rest of the world have more realistic Hitch/Ball weights and the whole of Europe have limits ranging from around 50kgs / 110Lbs up to around 250kgs / 550Lbs, And what ever Hitch weight the Trailer Is needs to be subtracted from the Tow Vehicles GVM ( Loaded Weight ) Because the Hitch weight then becomes part of the Tow Vehicles Load. IE If a pickup has a 1000kg /2204Lbs Load Capacity and you add a 3500kg 7716Lbs Trailer to the Tow Vehicle using that 20% ratio = 700kgs / 1543Lbs which leaves a total 300kgs / 661Lbs of load capacity left for the Tow Vehicle to Legally Haul ,
So Now you are down to 300kgs or 661Lbs of Load Capacity left, add to that 5 Adults weighing 80kgs / 176Lbs each = 400Kgs / 881Lbs which now puts that Vehicle 100Kgs / 220Lbs over it's Legal weight Limit, And in the case of an Accident Places the Driver In All Kinds of legal Trouble even more so in the US where it seems to be the custom to Sue everyone,,
The Bottom line is a trailer with a lighter Hitch load of say 100 to 150/175Kgs ( 220Lbs - 385Lbs ) is a far safer way to go because the excessive down force is not taking the weight off the front Axle of the Tow Vehicle and the Upside to that is you still have some Load Capacity left within the Truck,
There is nothing heroic about massive Tongue / Ball weights, in fact by towing with such a heavy Ball weight all you are doing is restricting your Load Capacity or GVM of the Tow Vehicle, My Truck has a Ball/ Hitch weight of 115kgs / 254Lbs yet I can still Tow a 2900kg / 6393Lbs Trailer with a combination weight of 5410kgs / 11927Lbs, Baring in mind it is an SUV with a 700kg / 1543Lbs payload,
To get and Idea of what a 115kgs of weight feels like on the back of a Truck/SUV Remembering that that 115kgs/254Lbs is sitting 1 Metre / 40"inches +/- behind the back Axle, so try holding your arm out straight and then get someone sit a 15Lb Sledge Hammer on your finger Tips and see how long you can hold it there, That 115kgs/254Lbs is equal to about 845ft Lbs because it is 3.33 feet behind the axle and the longer/further the Tow ball is from the centreline of the Axle the heavier that load is. A 350kg / 771Lbs at 40" inches is equal to 1050Kgs or 2567.43Lbs.
Sorry Guys but this subject is way more involved than just picking 10 or 20% of the Trailers gross weight, On a light weight Trailer you can add a bit more weight as long as that figure is below the Vehicles RATED Hitch weight, NOT the Hitch Companies Hitch Weight Rating. But be warned because you might have the same Vehicle as me but depending where you are in the world All of these Hitch Weights vary from country to country for the same vehicle.