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Old 01-18-2013, 02:46 PM
invisihitch invisihitch is offline
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Location: Atlanta
Join Date: Nov 2012
Posts: 431
Mein Auto: 2012 X3
Thanks Jay. Very much appreciate the encouraging words. And I agree that the two hitches are very similar in their overall design approach. But in my opinion their construction is actually more different than similar.

As for the similarities, it is not by coincidence that the high-level designs of the two hitches are so similar. BMW imposes several design constraints that we must work within if we want our hitches to be BMW OE hitches. To point out one such set of constraints, the hitch must attach to the vehicle at the rear chassis studs and only at the rear chassis studs. The flat plates that rest on the chassis must be of a minimum area, and the hitch must not touch any frame member or body panel elsewhere. (The purpose of this particular set of constraints is to fully preserve the function of the vehicle's crumple zones in the event of a rear-end collision). Hitches that do not satisfy all of BMW's design constraints will never be offered by BMW anywhere in the world so, of course, we all comply. And once you satisfy all of the constraints, you end up with pretty similar looking products.

As to construction, however, I will point out that there are no welds on the invisihitch that are load bearing or subjected to shear forces. Instead, our steel plates completely collar the hitch beam at every connection. Our welds simply keep the collars from sliding on the beam; they are not load-bearing welds at all. The same cannot be said of the other hitch. The most obvious example can be seen in the center of the two hitches. In an emergency braking situation with a heavy trailing load, those center welds on the competitor's hitch will bear the full force of 6,000 lbs trying to torque those welds off. In fact, normal repetitive towing with stopping and starting will constantly try to rock those two welds back and forth.

If a hitch ever fails, you want it to fail through deformation. That is to say, you want it to bend... bend very badly even. You never want a hitch to suddenly break and fail catastrophically in a way that could detach the trailer and the safety chains in the same moment. Our construction technique of collaring the hitch beam is done with purpose. It precludes catastrophic failure at any weld point. It is also one of the things that enables us to achieve the 30% higher international tow rating on the X5. But we do the same thing on all our hitches, even those for the Z4 that likely will never carry anything heavier than a bike rack.

I suspect this is far more than you wanted to know about hitch construction. But it's important stuff if you happen to make your living designing trailer hitches. Or if you tow heavy...


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