Hitch

[drgeeforce]

Originally Posted by JCL

Yes there is, that is what the unibody is made out of.



That is just wrong. Push down on the centre of the roof. It deflects. Push down on the top of the A pillar. It doesn't deflect. Guess it must be stronger.

I understand that the fore-aft strut attaches to the subframe crossmember, from your description, but that doesn't change the fact that the hitch is hung on sheet steel.

Triangulation only matters if the apexes are solid. Also, the OEM mounts don't achieve a box section, rather, they attach to the box sections. They are the strong part.

Can I be one of the purists?

Unibodys are typically made of tubular steel in a hydroforming process exclusively, for MSLA and HSLA steels. [http://wardsautoworld.com/ar/auto_chassis_frames_new/]

No, there are no strong points on the rear vertical except for the D-pillar which is reinforced by wedges. [Body stiffness is further increased by wedges on the rear lid at medium height on the two D-pillars when closed. High strength(MSLA) and ultra-high-strength(HSLA) steel is used at the rear end of the new BMW X5 in order to achieve optimum stiffness and load resistance in a rear-end collision despite minimum use of material.
http://www.carbodydesign.com/archive/2006/08/12-new-bmw-x5/]

This is not where your OEM hitch attaches to. The 2-bolt flange attached to the 'ends' of the box section(aka unibody) is not attached to any subframe nor is there any reinforcement pillar. Only 2 bolts attach the mount/flange to the longitudinal box sections. The telescoping mounts replaces the rear bumper absorber and via a square tubular mild steel crossmember is saddle-welded to an offset receiver. Leaving the hitch on defeats the original BMW safety designed crumple zone where the monocoque chassis will deform inward in a crash-tested, controlled manner.
http://www.cars.com/go/crp/buyingGui...rer=&year=2006
http://www.autoweb.com.au/cms/A_5567...wsarticle.html

Using your logic, the longitudinal box sections are sheet steel also.

BTW the six holed mount is the longitudinal box section crossmember(aka sheet steel). see the second picture http://www.xoutpost.com/articles/x5/m...tion-tips.html

Leaving the OEM hitch on alters the f/r weight distribution.

Lack of an impact absorber causes 100% of the collision forces directly onto the longitudinal box sections. If impact is off center, shearing forces will be predominant, again defeating the crumple zone.

I guess your opinions are just that, opinions.
Purists don't leave their hitches on.