Incomplete answer.

Tongue weight is specified as 600 lbs, on smooth roads, for a load applied no more than 8" horizontally from the receiver pin to the ball. BMW tech documents provide a drawing for that. I have posted it here before. There is also a maximum vertical drop. It is clear that there is a bending moment limitation, from that specification.

So, if you apply the load at 24" (pin to CoG of the load) then you have a 200 lb capacity.

Also, the smooth road limit is because of bouncing. If you have a bouncing load, often related to off road use, the 600 lbs goes down considerably, to 330 lbs. A bouncing load at 24" CoG would have a 110 lb load limit (including the carrier). Hitch balls don't tend to bounce so much, because they apply the load close in to the support point.

This is all important due to the number of carriers that result in bent hitches. People think 600 lbs, think they can apply that load at any location, go over bumps that cause the load to bounce, and are then surprised that their 6000 lb hitch failed.

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