Black & Tan 332iT

[Obioban]

Need to get a scan of the CSL's in the mix.

[Bry5on]

Oh, clever!

Kinda blown away by the findings. They're far more different than I though they were.

Honestly, same reaction I had. Almost didn’t believe my eyes as it’s clearly a derivative but a totally different forging.

First principles has the on center steering ratio at 16.33:1 for an M3 CSL/ZCP and 15.4:1 for my knuckle. Recall that the 992 ST is 15:1 in center, but 13.5:1 after accounting for wheelbase differences. So even with the ratio shorter than the non-m, we’re still a ways off the sports car.

[heinzboehmer]

Oh, clever!

Kinda blown away by the findings. They're far more different than I though they were.

[Bry5on]

I lined them up on the mounting bosses for the heat shield as I believe that’s a shared part number. Lots of geometry tweaks, ones I’ve noted (M3):
- Caster (increase)
- Trail (increase)
- Inner tire clearance (slight increase from moving strut inboard)
- Ackerman (decrease)
- Scrub (increase)
- Bump steer (hard to say direction, but probably decrease)
- Caliper clocking, radial- and back-spacing

[heinzboehmer]

Huh, that's surprising. Static camber and caster (and toe?) look different too?

I would trust the geometry of the pickup points for the LCA, tie rod, strut and caliper brackets in the scan. Not sure I'd trust the relation between the hub and the aforementioned features, though. The heat shield was hard to wrap the scan around.

What happens if you line the scans up on the LCA/caliper bracket mounting points? I would think those are the same between the M and non-M knuckles. Almost looks like the non-M tie rod pickup point would end up higher than the M one, resulting in a slight change in effective LCA to tie rod distance.

[Flow]

The amount of knowledge in this thread is insane.
Thank you for doing all this and sharing it with the community !

[YoitsTmac]

Insanely interesting to see the two overlapped. Looks like the caliper bracket position is tied more to the strut than the LCA.

The BMW community can always depend on me to have the most random parts lying around🫡. Got home and immediately chucked that thing in the bin.

[Bry5on]

Thanks to YoitsTmac and heinzboehmer we've got an interesting finding. I've overlaid a non-m knuckle scan to an M3 knuckle scan, and the numbers do not match the BMW quoted steering ratios.

So here's what I've got for LCA to tie rod distance:
M3: 130mm
Non-m: 126mm
SuperKnuck: 122.9mm

That means that if M3 CSL/ZCP is 14.5:1, then
Non-M: 14.05:1
SuperKnuck: 13.7:1

And consequently, if the non-M is 13.7:1, then
M3 CSL/ZCP: 14.13:1
SuperKnuck: 13.36:1

Now I'm going to have to pull up the numbers in NCS expert to see what the DSC module says. Guess that knuckle I ordered is a bit of a tighter steering ratio than planned!

Blue is M3, brown is non-m:

[heinzboehmer]

I need to schedule time with him. I'll just bring that as an item and we can scan it for you!

Yep! Need to meet up with both you and Slideways in the not too distant future. The list of things to scan is growing longer every day

[Bry5on]

I need to schedule time with him. I'll just bring that as an item and we can scan it for you!

Love it. Thank you!

[YoitsTmac]

Yeah at some point here I'll make the trip up. Or Heinz can scan it

I need to schedule time with him. I'll just bring that as an item and we can scan it for you!

[Bry5on]

I have one rusting on my back patio. You making a trip back up? They're much easier to get ahold of though.

Yeah at some point here I’ll make the trip up. Or Heinz can scan it

[YoitsTmac]

I have one rusting on my back patio. You making a trip back up? They're much easier to get ahold of though.

[Bry5on]

For what it's worth when I was looking into those adjustable tie rod kits with some track nuts, someone said the E46 M3 knuckle retains good geometry and minimal to no bump steer when lowered and doesn't need nearly the correction a Non-M could.

As someone who daily drove a non-M for over a decade, most lowered (like my now M3), I can confirm I never even think about bump steer anymore. I'm also not an engineer and am unaware of other negative drawbacks when lowered.

That’s interesting, I wonder if this is what drove the steering ratio change? Would be interesting to scan a non-m knuckle and overlay them as I’d be surprised to see much of a difference.

[Obioban]

Center of the wheel to fender is the number I’m looking for, just in the vertical plane

13mm lower than nominal as measured purely in the Y.