Black & Tan 332iT

[Bry5on]

Thanks to George Hill I believe we’ve found the remaining flexiness in the front suspension. George has an e46 front clip handy (the man has dedication), so during a visit to TX we ran a test yesterday to prove my next hypothesis. With the fender off, we attached a dial indicator as in the image below, measuring longitudinally, then I pushed on the fender mount vertically with about 40lbs by hand. You could see the dial indicator move .002” from this ~40lb push. This is significant because just sitting on the ground, the car sees about 20x that load, meaning it’s displacing about .040” or a full millimeter from just placing the car on the ground. View of what’s behind the right front fender, with dial indicator setup:


So every time your suspension loads/unloads or hits a pothole/bump, this joint is flexing and allowing the strut tower to move up/down out of sync with the car. This will be noticeable in driver feel.

So we took some scans, including of the other side which had a pothole damaged tower, and I’m going to design some gusseting that will live invisibly under the fender to stiffen the front suspension up nicely.

Thanks George!

[m3_tristan]

You can reach out to @limited.slip on instagram if you’d like to pick one up that’s ready to rock! I just don’t have the free time to pack, ship, distribute.

thanks! I just shot him a message.

[Bry5on]

Sorry new to the forum. Are you selling the csl ducting?

You can reach out to @limited.slip on instagram if you’d like to pick one up that’s ready to rock! I just don’t have the free time to pack, ship, distribute.

[Obioban]

Fits great! Rough math says that the 4 cabrio fasteners will see about 60% of the load of the original 8, and this brace will certainly be stiffer inherently. So an upgrade on paper. No real noticeable change, but it's definitely not less stiff. It's getting hard to do the driveway test as the car isn't making much creaking in the door sills unless it's pretty extreme.

Ordered

[m3_tristan]

Another win today.

This evening I decided to install the first version of the v-subframe-brace.

As a recap, the hypothesis is that:
1) The remaining rear bump oscillations I felt after installing the X-brace are related to a lack of fore-aft/bending stiffness
2) The subframe can rock forward aft, sort of 'around' the axle axis, under throttle application, related to subframe mount failure, and the stock v-brace is not enough to constrain this movement
3, unstated so far) The m-clunk is related to 2) and additionally, the subframe floor acts as a bit of a speaker, amplifying the clunk






I wasn't thinking for a bit and ended up installing M6 rivet nuts instead of M8 rivet nuts, probably because I decided to do this on jack stands instead of driving the 2 miles down the street and getting on the lift. At some point I may try to remove the M6 guys and go to M8 as the design intended, but we'll see how we get along for now.

Early days and not a whole lot of seat time but I can say reasonably confidently that the hypothesis has been validated, and this brace mitigates a lot of that flexibility.

Response and oscillations following bumps are much tighter, and throttle applications are more 'instant' and don't have that coil-up feeling that the e46 has. You can be a bit rougher with throttle application and removal and it doesn't feel as rough on the chassis, it just follows your foot.

I've only got a handful of miles on the car, attempting to provoke it of course, but so far I haven't been able to get it to m-clunk. You can for sure get it to cluck by going on/off/on/off throttle very quickly, but this is true even on the newer G80 cars. Shifting feels a little smoother? Not so much in the lever, but in the car itself. Definitely need more miles to validate this.

On top of that, it does seem to be even more torsionally rigid when exiting extreme driveway angles. I can tell again that the front is less rigid than the rear. I wonder if recreating the e30 cabrio front strut mount gusseting would be useful. I'm really going to have to do those control arms and a new set of bushings now.

Anyway, pleased with this! The car has really transformed a generation or two in ride feel in the past few weeks.

Sorry new to the forum. Are you selling the csl ducting?

[Bry5on]

Let us know how it fits! I’m curious why the m3 vert didn’t get it.

Fits great! Rough math says that the 4 cabrio fasteners will see about 60% of the load of the original 8, and this brace will certainly be stiffer inherently. So an upgrade on paper. No real noticeable change, but it's definitely not less stiff. It's getting hard to do the driveway test as the car isn't making much creaking in the door sills unless it's pretty extreme.

[Obioban]

Pretty sure those other 4 holes are nearly useless if you have just the diagonals.

I may have ordered a cabrio brace a week ago… it’s taking forever to ship, so at some point I’ll get it.

Also pretty sure I won’t be able to feel a difference, but who knows!

Let us know how it fits! I’m curious why the m3 vert didn’t get it.

[Bry5on]

Seems like the vert brace is missing some mounting holes?

Pretty sure those other 4 holes are nearly useless if you have just the diagonals.

I may have ordered a cabrio brace a week ago… it’s taking forever to ship, so at some point I’ll get it.

Also pretty sure I won’t be able to feel a difference, but who knows!

[Obioban]

What was that? I couldn't hear you over the sound of a drill 😬

The existence of the vert brace certainly gives credence to the idea that this is a useful area to brace.

…. curious that the m3 vert didn’t get it…

[IamFODI]

Seems like the vert brace is missing some mounting holes?

What was that? I couldn't hear you over the sound of a drill 😬

[Obioban]

Seems like the vert brace is missing some mounting holes?

[heinzboehmer]

https://www.motorsportparts.nl/bmw/bmw-e46-z4/body/e46-dubbele-tunnelbrug---1-stuk

Been done already, karter16

Oooh, very nice. Thanks for the link.

Any idea on weight? Convertible piece is 0.946 kg according to realoem.

[bmwfnatic]

In case you want to do some more pondering: https://wilhelmraceworks.com/blog/me...ssis-stiffness

I'm currently pondering about the best way to build a similar thing for myself to get data from my car. Would be awesome to be able to quantify these changes instead of trying to feel them out.

About the tunnel brace, I think a plate sandwiched between the stock parts would yield the most gains for the least effort. Boxing the stock parts in would be even better, but that requires welding. Non-M part is likely the best answer though.

https://www.motorsportparts.nl/bmw/bmw-e46-z4/body/e46-dubbele-tunnelbrug---1-stuk

Been done already, karter16

[Bry5on]

I think I used M8x1.25 x 16mm button (and e-torx, because why not make it complicated) head screws, I will have to double check length. Then just M8x1.25 rivet nuts with 2mm ground off the nose so that they’d fully seat into the subframe before hitting the upper wall. Installed wet with POR-15 to prevent rust just in case.

edit: I ordered some of these to test grip range. Will report back: Low-Profile Rivet Nuts, Tin-Zinc-Plated Steel, M8x1.25 Internal Thread, 15.2mm Long

https://www.mcmaster.com/91230A011

Ok this is definitely the right part for this application. Should fit in the available space and installs into a .500” hole

[Bry5on]

What hardware did you use?

I think I used M8x1.25 x 16mm button (and e-torx, because why not make it complicated) head screws, I will have to double check length. Then just M8x1.25 rivet nuts with 2mm ground off the nose so that they’d fully seat into the subframe before hitting the upper wall. Installed wet with POR-15 to prevent rust just in case.

edit: I ordered some of these to test grip range. Will report back: Low-Profile Rivet Nuts, Tin-Zinc-Plated Steel, M8x1.25 Internal Thread, 15.2mm Long

https://www.mcmaster.com/91230A011