"In this Products Series, I document the development of the high strength carbon front subframe braces for the E9x M3, E46 M3 and F8x M2/3/4.

In this entry, I get excited about a new application of carbon on our BMW M3's chassis, only to get hustled out of money and dragged through the mud by a forum creature."
- Matt

The original gambit. 

2024 is set to be the Stripper's journey into increasing chassis rigidity and reducing weight without sacrificing daily drivability. 

Avoiding compromises between rigidity and weight is a technical challenge in itself. If said challenge can be surpassed, it's most often at an extremely high cost for diminishing returns. 

I was focused on testing lightweight machined aluminum suspension components in the Kinematics program along with the development of new lightweight carbon body panels.  

Something of interest. 

In January '24, I came across an intriguing Facebook marketplace listing in one of the E9x M3 groups for a carbon version of the original belly pan.

The original aluminum belly pan is designed to brace and protect the frame rails, subframe, steering column and the oil pan. The BMW TIS states that your car should not be moved without the belly pan installed as it acts as a structural chassis component.  

My original intrigue was over reducing weight at the front - a notably difficult challenge on our M cars.

I had seen some companies create carbon undertray, yet they never made much sense to me: the OEM unit is light and the aluminum replacement I use is just as light, and stronger.

A lighter belly pan sounded useful: carbon could be as stiff as aluminum, for much less weight.

Here's my E92 without its belly pan, it's fully exposed. 

The original aluminum belly pan also serves as a potential jack point, further indicating this was a structural component. 

Deal made. 

I contacted the seller over marketplace. Turns out I had previously chatted with him on forums. He's a well known member of various BMW forums and an avid E46 M3 track guy that makes his own carbon products.

He was planning to develop his own set of E46 M3 doors and had been curious about the set I tested. He had also made his own hood and headlight blanks and was looking to expand his operation.

He was selling this for cheap as he had previously used it. He'd normally sell this for 9xx$ USD. 

Pictures speak for themselves.

We worked out payment, I sent a shipping label and the carbon belly pan showed 2 weeks later. 

It wasn't looking good - there were many issues at first glance. 

Let's run through the concerning sections, starting with the carbon manufacturing process.

Vacuum infusion.

The belly pan had been manufactured using vacuum infused carbon. It's a "wet" process most noticeable by the epoxy residue. It’s for it's low upfront costs, and relative ease of use. 

The process is noticeable by the left over resin, seen by the “wet” appearance.

Here, the commonly outer surface was the underside of the part, unseen if it was installed.

This potentially indicates this part was created without an actual mold, using the original belly pan as the positive mold over which carbon was laid. 

This was evident in the bolt holes, this technique leads to shapes being slightly off, on top of the crude cut outs. 

Foam core’d.

Upon closer inspection, the belly pan had been manufactured using a foam core. It's a carbon manufacturing process most often seen in automotive applications for undertrays as it's lightweight, stiff, and cheaper than equal weight carbon. 

The foam was noticeable in the grossly cut sections.

Safety hazards.

There is no free lunch when it comes to composites manufacturing, a foam cored part will be subject to a simple triangle of variables.

1. Heavier and more rigid than a single carbon layer of equal strength.
2. More rigid and weaker than a single carbon layer of equal weight.
3. Lighter and weaker than a single carbon layer of equal rigidity.

#3

We knew its weight.

Without knowing the exact carbon and foam core used, we cannot be certain of its strength and rigidity. I started worrying when I dug into Jae's carbon manufacturing process. 

It's a relatively safe assumption that this carbon brace was weaker, and less rigid than stock considering its much lighter weight. In the context of a structural brace, this was excessively bad.

I further validated my assumptions by showing this piece to various trustworthy, professional carbon manufacturers and engineers in Europe. They all expressed safety concerns.

We tested fitted the brace plate on another car. Holes were misaligned and needed to be further drilled out, one of them sheared in the process. 

For the first time ever, I opted to not test a product on my own car. 

Creatures.

I contacted Jae via Messenger with a friendly, cautionary heads up which was unfortunately left unanswered. He took the time to comment on my post announcing an improved version. 

In early June, Jae posted about his carbon doors on an E46 M3 group. A member was curious about the carbon processes he used.

Jae preferred not to disclose the information and felt the need to insert me into the conversation. I posted facts about his work. He blocked me on Facebook.

Credits.

In retrospec, I thank Jae for creating a carbon variant of this OEM structural component. I'm thankful for his behaviour later on, demonstrating he wasn't ready to offer a commercially viable product with the required level of service. 

Still, this application of structural composite technologies was of high interest. 

We could potentially increase rigidity, and reduce weight at a fair price. 

Up next: we tackle this product development with a professional engineering approach.