OEM Trailer Hitch

[JCL]

Originally Posted by xsx450

I get what you guys are saying, but you are just SAYING. I am doing. They are not bolted to sheet metal, or the floor pan. This is not one of those mounts that screws through your spare tire floor in the trunk.

It appears that the Reese cross bar bolts on to item 14, in the parts book drawing attached. That is a lateral tie piece that holds the two axle supports (2 and 3) from spreading apart. It is not strong in the fore/aft directions, unless you through-bolt to item 1 (not sure if your hitch does that, or not, as some do). It shows as being braced to item 1 in any case. Item 1 is the trunk floor. Item 14 is braced to the trunk floor because it isn't very strong by itself, it is very thin. It is the piece that BMW discards in their OE hitch installation. So, it appears that despite your claim, this is one of those mounts that is attached, either directly or indirectly, to the spare tire floor in the trunk.

All of our equations mean jack because for one they aren't accurate, and two I have loaded up over 900 lbs on this thing over 24" out of the hitch, jumping up and down. No stress fractures, no tearing subframe. Nothing.

This equation is totally accurate. The math is pretty simple. The design load is published as 600 lbs vertical at 8", if you use the reinforced OE hitch. You have applied 1.5 times the rated load, at 3 times the rated distance. That is 4.5 times the design load. Glad that worked out for you. Some of us just believe that some calculations do mean something. You don't have to agree, you are certainly entitled to your own opinion. You are saying that because it hasn't broken yet, it is strong enough to last forever, that fatigue isn't a factor. OK.

As an aside, the strength of the front bolt doesn't matter. It is strictly a locating point. All the force from the hitch stabilizer bar at that end is upwards, not downwards, so the bolt doesn't see any significant stress.

The failures that we did see back in the early days of the X5 were in fact to the rear pan, item 1. Yes, it was ripped off. Repairs were expensive. That was why the aftermarket hitch manufacturers added that longitudinal brace. They also include a line in their hitch warranty that states that they do not guarantee that the hitch is fit for use. Their 6000 lb rating is likely based on bench tests of their hitch in a jig, not on having it mounted on a vehicle. We all accept that it has a 6000 lb rating, just not that their way of rating the hitch has any relevance.