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Old 11-11-2018, 09:53 AM
bfeng bfeng is offline
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Quote:
Originally Posted by bono View Post
I think that the mounts to the unibody are strong with significant margin. I agree that the long drop plates between the cross bar and the receiver are the weakest point. Therefore, I reinforced the hitch, including adding a metal strut between the receiver and the axle carrier (Can-am type of mod, if you want to google for photos). I am using ProPride hitch, which probably generates more stress on the receiver than usual WDH. No problem so far.

The BMW hitch design is not as good as other German SUV's, and I have less confidence in its design for overloading or WD. I say this even though I've had no problems in 2 years of towing a 5000lb rig and a few trips with a 9000lb trailer with a big arse WD setup. Everything remains tight and the hitch has not shifted or bent even 1mm.

But while our old SUV (W164) has a similar tubular hitch but it's overall stronger in construction plus it has 2 cast iron torsion arms that extend almost 2ft up into the uni-body bumper reinforcement tubes. These help both with distributing the tension load away from the 8 bumper mount bolts and provide support for rotational or torque loads due to high tongue weight or WD.

Mercedes instructions to us did not exclude use of WD but BMW does. So, depending on what and how you tow, I'd be careful about assuming how much safety margin you have in the hitch and the attachment to the vehicle body.

Of course you are right that all OEM's design in safety margin and validate OEM parts/designs with very rigorous testing that goes beyond the recommendations in the official user documentation. But unless you know the specifics of the test, I'd err on the side of caution.

If you are going to regularly tow 20-30% over the rated limits and use 1500lbs of WD torqe, I'd highly recommend you have the hitch and it's attachment scheme strengthened. Any good automotive custom fabrication shop should be able to help with this work.
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