heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

I am curious why it didn't come from the factory. As in, the Z4M did, and wasn't that much later.

It seems like it's one of those big generational jumps. E9x is way stiffer than E46 and every car of the E9x era has some version of these triangulation braces. E85/6 is a weird E46/E9x hybrid and it lucked out with the E9x chassis rigidity.

Think we're just slightly too old and missed out on that.

Also, just for fun, this is the bracing in the F80 M3. Again, way stiffer than the previous gen, but man, it essentially needed a full exoskeleton to get there:

[bigjae46]

It seems like it's one of those big generational jumps. E9x is way stiffer than E46 and every car of the E9x era has some version of these triangulation braces. E85/6 is a weird E46/E9x hybrid and it lucked out with the E9x chassis rigidity.

Think we're just slightly too old and missed out on that.

Also, just for fun, this is the bracing in the F80 M3. Again, way stiffer than the previous gen, but man, it essentially needed a full exoskeleton to get there:

As you can see the F8X has a much beefier front crossmember/radiator support that the E46 which is long spans of flimsy thin gauge steel. I wonder how much of a benefit there is in improving that.

[George Hill]

As you can see the F8X has a much beefier front crossmember/radiator support that the E46 which is long spans of flimsy thin gauge steel. I wonder how much of a benefit there is in improving that.

Bry5on

[Bry5on]

Man, good question. You can see how well supported the frame rails are with the stamped and tubular braces, then that it is boxed in to the strut towers and the lower subframe and frame rails. This would be pretty effective in torsion but I’d wager less so than the things we’ve already done. Also way harder to package in the e46 engine bay I think.

To do something like this, you’d want to modify the auxiliary fan support to tie the two frame rail attachments into the upper core support, then triangulate that to the strut towers. Then you’d need to essentially build a mini front subframe that could tie back to the frame rails in front, or maybe pick up on the sway bar mounts as that’s what’s doing the frame rail twisting. Tie that mini front subframe into both the aux fan support and the existing subframe. A lot of work.

[heinzboehmer]

To do something like this, you’d want to modify the auxiliary fan support to tie the two frame rail attachments into the upper core support, then triangulate that to the strut towers. Then you’d need to essentially build a mini front subframe that could tie back to the frame rails in front, or maybe pick up on the sway bar mounts as that’s what’s doing the frame rail twisting. Tie that mini front subframe into both the aux fan support and the existing subframe. A lot of work.

BMW does something similar to what you describe with their modern cars. Here's a G30 for reference, since that's the simplest implementation I came across during my research:



They skip the "mini subframe" thing you're talking about and just do the frame rails to the radiator support part. Probably because the actual subframe is extremely beefy and spans a good chunk of the front end. Other cars like the G80 have a separate v brace going from the frame rails down to the subframe.

But anyway, the G30 braces go from the top of the frame rails to the top of the radiator support and then another set of braces go to the strut towers.

Forward facing strut tower pickup points on the E46 would be fairly easy to do by bonding in the E85/6 brackets (or similar):



But yeah, sounds like packaging would be pretty hard. I think there might be room to squeeze the diagonal braces in between the aux fan and the kidneys, but can't say for certain. Then you'd need to clearance a good chunk of the front shrouds to be able to snake the strut tower braces through.