What models does the Z4 (partially) share the rear chassis with? (for fitting a towbar/hitch)

[BKR]

Hi,

I'm looking to install a towbar on my E85 Z4, but the one available is an insane €700 or so. Towbars for the E46 3e are available at €150. I have compared them and they really look alike. Perhaps they'd even fit, albeit with a slight modification. That's no problem, I have proper welding equipment. So you can guess where i'm going at; i'm looking for a towbar originally designed for another model, to fit to my Z4. I know regulations might have a say, yadda yadda, but it'd be just for incidental use. The Z4 isn't allowed to tow anyway, so i'l only use it for a towbar box or a bicycle carrier.

I'm looking for the model with the most similar or identical (rear) chassis or bumper bar construction when compared to the Z4. The E46 seems alike, but since the Z series is always designed for the 'zukunft', the future, it may be more similar to the next gen of other series, like the E90. In any case, I found all the technical drawings for the towbar of the Z4, so they can be compared properly with another model:
https://www.kupplung.de/out/media/103408-04924-1-samples-v2.pdf
The width between the centrelines of the chassis beams is 907.2mm.

I know it'll save me €500 at most, but I've just bought a house and the Z4 so i'm already being financially irresponsible 8) hence i'd like to reduce costs for things like this.

Thanks for any help, and other creative solutions to carry more luggage, as well as drawings of the Z4's and other model's chassis' are also welcome! I'm aware of the boot rack, but that doesn't add much capacity.
EDIT: I added the term 'hitch' to the subject so our American fellows on the other side of the pond will also stumble upon this thread when using their terms to search for info.

 

[Smartbear]

Hi, e89 comparison here

Rob

 

[BKR]

Hi, e89 comparison here
0F1B7527-ADF1-4739-9234-3A1A77D68578.png
Rob

Much appreciated, as I understand the E89's chassis doesn't compare well to the E85's? I've found a similar kind of manual for the E85, but it contains no information on the chassis. I did mount a towbar under the E46 of my brother a year or two ago, and he happened to still have the bumper supports that you normally discard when mounting a tow bar, so lucky me. I can measure those to find out if a E46 towbar could perhaps be used and how it would need to be modified. I'll post the results once I have a conclusion.

 

[BKR]

Excellent news, I measured the E46's bumper supports and found out that the towbar construction is almost identical to the E85's.

I got bored last evening and reverse engineered the drawings of the E85 towbar and drew them in SolidWorks. The flanges with which it gets fastened to the chassis beams are identical in regard to the bolt/hole pattern. The extension and its bushing which inserts in the chassis beam is slightly different; it's 90° rotated. And possibly the bushing is of a different size, can't measure that since the bumper supports don't have 'em. But it wouldn't be much of an issue anyway.

I'm yet to measure the distance between the chassis beams centrelines to determine if the draw bar is the correct length, or if it has to be shortened or elongated.

Finally, the ball joint rod might be differently size, but that's just a matter of making an alternative cutout of the bumper. It seems that they're the same. The position of the ball joint in regard to the chassis beams seems the same also, so no worries about the balljoint ending up too low or too high. Pics are attached below, PM me if you'd like to have the 3D drawings.

I have drawn over a scaled and edited photo of the E46's bumper support gasket(pic 1), and I also measured and drew them(2). Then follows the manufacturer's drawing of the E85's flange(3), my measurement of that(4), and the overlay of the E46 and E85 pattern. A slight difference is visible, but I attribute that to discrepancies in measurements. The difference in hole size isn't really there, the gasket just has smaller holes to make an air tight fit. At the end, two screenshots of the 3D model are attached.

 

[DFR]

Excellent news, I measured the E46's bumper supports and found out that the towbar construction is almost identical to the E85's.

This is a great bit of research dude, thank you. I too was wondering if the tow bars for E46 would fit the E85. Thank you for confirming this. I'll see if I can find one as I am itching to get my bike with me when I'm out driving.