My current hypothesis is that this is caused by using a weight distribution hitch. I don't blame Bosal or Tesla at all, though I would very much have liked some guidance on the use of WD (neither provides any).
WD hitches create a stiffness between the trailer and the tow vehicle through the use of torsion bars. Once the bars are locked in place, the trailer is no longer able to freely rotate on the hitch ball. Depending on the rating of the bars, there can be quite a bit of stiffness between the two vehicles. When the trailer and the tow vehicle are on different planes, such as with uneven pavement or dips in the roadway, a force is exerted by the bars into the tow vehicle. In fact, this is precisely how the WD hitch is supposed to work in order to push some of the weight off of the rear wheels and onto the front wheels. In a welded receiver solution, the force is transferred directly to the vehicle unibody or frame. But in our removable hitch solution, that force has to transfer through the hitch socket before making it into the vehicle.
Compare this with a weight bearing hitch. The trailer and tow vehicle are able to move independently of one another with relation to the planes on which they travel. There are forces pushing on the socket, but they are only the forces of the tongue as it travels. Any twisting will be completely relieved at the hitch ball.
This is admittedly just a hypothesis. I plan to propose this to Tesla, and send them my entire hitch apparatus, including the bar, once I remove it. Hopefully they can do a solid investigation into it. If indeed it appears that WD is causing this, they could address it as simply as adding a blurb to the towing section of their Model X guide. "Weight distribution hitches are not supported by the stock receiver."
All of that said, I still wouldn't tow a heavy vehicle with the stock hitch. Having three ball bearings holding my entire trailer in place no longer gives me peace of mind.
WD hitches create a stiffness between the trailer and the tow vehicle through the use of torsion bars. Once the bars are locked in place, the trailer is no longer able to freely rotate on the hitch ball. Depending on the rating of the bars, there can be quite a bit of stiffness between the two vehicles. When the trailer and the tow vehicle are on different planes, such as with uneven pavement or dips in the roadway, a force is exerted by the bars into the tow vehicle. In fact, this is precisely how the WD hitch is supposed to work in order to push some of the weight off of the rear wheels and onto the front wheels. In a welded receiver solution, the force is transferred directly to the vehicle unibody or frame. But in our removable hitch solution, that force has to transfer through the hitch socket before making it into the vehicle.
Compare this with a weight bearing hitch. The trailer and tow vehicle are able to move independently of one another with relation to the planes on which they travel. There are forces pushing on the socket, but they are only the forces of the tongue as it travels. Any twisting will be completely relieved at the hitch ball.
This is admittedly just a hypothesis. I plan to propose this to Tesla, and send them my entire hitch apparatus, including the bar, once I remove it. Hopefully they can do a solid investigation into it. If indeed it appears that WD is causing this, they could address it as simply as adding a blurb to the towing section of their Model X guide. "Weight distribution hitches are not supported by the stock receiver."
All of that said, I still wouldn't tow a heavy vehicle with the stock hitch. Having three ball bearings holding my entire trailer in place no longer gives me peace of mind.