OEM chassis stiffening with convertible parts

[squashman702]

Did a bit of searching, but didn't find anything on the topic. After parting out several ZHPs in all of the various body styles, it seems that BMW did some factory chassis stiffening to the convertibles. I've noticed the major reinforcements as follows:

-Late convertibles got an aluminum radiator support. I've seen this in 2005/2006's. I'd think this would take some of the flex out of the front end versus the stamped steel pieces used in sedans. EDIT: Looked at the sedan that I have as my next parts car, and it has an aluminum piece at the top of the radiator support, although the rest of the structure surrounding the fan area looks different.
-V brace under the rear subframe to trunk pan. Not sure if this is a direct bolt on to the sedans?
-Exhaust mount across transmission tunnel is much larger and aluminum in the convertibles instead of two pieces of steel like in the sedans. I believe this would swap over but haven't verified fitment.


Wondering if anyone knows of other differences, and if there has been noticeable results by moving some of these parts to a coupe or a sedan?

[cakM3]

I will tell you that the aluminum front radiator support should carry over to the sedan. At least on coupes they work out very well as I have already done this for my M3. I have an extra aluminum front radiator support that will be installed on my sedan when I get to it sometime this summer. Having this adds more support to the front as I have noticed on my M3.

[Galapolis]

Best chassis stiffening you can do is the sedan backplate (https://cmpautoengineering.com/collections/all/products/e46-front-bolt-in-brace). It should fit on all coupes. Not on convertibles though.

[John in VA]

Best chassis stiffening you can do is the sedan backplate (https://cmpautoengineering.com/collections/all/products/e46-front-bolt-in-brace). It should fit on all coupes. Not on convertibles though.
Interesting - this is the first I've heard of this. Is this. indeed, the piece? Would love to "just" bolt it in behind the seats, but looks like you might need the lower weld-in piece, too.
E46 Front Bolt In Brace
https://cdn.shopify.com/s/files/1/0320/3068/7367/products/E46FRACPRB-1-min_540x.png?v=1662529980

[Galapolis]

Probably best to reach out to CMP about specifics like that.

[t.er]

Seems like you could install a few rivnuts, don't necessarily need any welding

[squashman702]

I will tell you that the aluminum front radiator support should carry over to the sedan. At least on coupes they work out very well as I have already done this for my M3. I have an extra aluminum front radiator support that will be installed on my sedan when I get to it sometime this summer. Having this adds more support to the front as I have noticed on my M3.

Nice, good to hear first hand experience with the swap and that it made a difference. I'm going to pull the sedan radiator support that I have shortly, so I'll be able to get a good look at the differences.


Best chassis stiffening you can do is the sedan backplate (https://cmpautoengineering.com/collections/all/products/e46-front-bolt-in-brace). It should fit on all coupes. Not on convertibles though.

This looks like a nice piece, been thinking about building something similar for my car with DOM tubing.

[cakM3]

Nice, good to hear first hand experience with the swap and that it made a difference. I'm going to pull the sedan radiator support that I have shortly, so I'll be able to get a good look at the differences.

I think when you pull the sedan front radiator support and compare it to the vert front radiator support, you won't find any differences. It should be a direct swap. :thumbsup