Black & Tan 332iT

[Bry5on]

Test fit of the heat shield went well, miles of clearance to the tie rod and control arm. Definitely room to play with ackerman if one so desired, or to move KPI and scrub radius a bit.

Anyone here have a 3D section model of the CSL/ZCP or regular M3 brake rotor? Looking for a few key dimensions to verify clearance as I modeled my shield off of a factory M3 heat shield scan.

[Suspension Decoder]

Here’s the spreadsheet - for accuracy with roll and travel you’ll need to enter CG height as well as the corner weights. It seems a stock M3 is around 21” and a weight reduced track M3 might get as low as 19” based on the measurements I’ve seen so far. The sheet will also calculate new weight distribution numbers for added/removed mass in x, y, z coordinates. Some of the assumptions that simplified the model came from my 3D model of the suspension geometry, which I think is hyperlinked from the excel doc somewhere in there.

Im pretty busy with my day job (I’m also a mechanical engineer, mostly rockets, spacecraft and automotive body in white work to date) so I don’t think I’ll be able to coordinate anything within the next couple weeks but maybe heinzboehmer and or tlow98 can take you up on that as they’re local to you on the peninsula. They’re both also engineers with similar OCD and are quite familiar with my car and its various developments.

Personally I find 1.9/2.1Hz a little high for me but I’m open to new takes with more appropriate damping. Prior cars in the last two decades have had lots of custom suspensions (all pitch balanced, roll centers in the right place, I did my homework) and I usually find that for my daily driver I enjoy about the 1.6 Hz range. Any more than that and it seems to trend too far down the “GT3 daily driver” spectrum for me. My last 991 911 had an aftermarket controller on the sport PASM dampers which helped a lot during daily driving but ultimately I wished for a softer/longer spring even so. I think that car was up to 1.7/1.8 or so in the rear if memory serves?

In any case, excel sheet here: CG location change_332it.xlsx

Thanks for the spreadsheet and notes. Understood on your time constraints. I'll ping heinzboehmer and tlow98 individually or see if we can coordinate a group meet. There's an event on Sunday in Morage 'Estate of Mind' I'll be attending as a vendor. We'll have Christina there plus an F31 328xD wagon with FCM Elite Stage 3 Ultimate at ~1.6 / 1.8 Hz.

I agree that for more comfortable daily-driving, capping the rear at ~1.8 Hz is ideal. Transmissibility starts to increase rapidly above 1.8 Hz. I used to daily 2.2 / 2.4 Hz and with all the wizardry I can employ, it was quite tolerable. Now, with even more enhancements to high-frequency noise reduction (Ripple Reducer) and further optimization of damping ratios (it's amazing how little you really need when you get Flat Ride set up properly), at ~1.9 / 2.0 Hz Christina feels better than most sports cars from the factory - and has more grip as well. 1.3g on 255's (200 treadwear BF Goodrich Rivals).

The 991s when you include bump stop interactions are well north of 2 Hz. Those Porsches are a bit of a mess. Even on springs alone, Porsche has continually increased the base ride frequencies every generation. I think the 991 is the first when they didn't overdamp the holy heck out of the suspension, but it still has a strong rebound bias and is far from optimal.

If / when I meet up with the Peninsula M3 crew, they can report their observations back to you.

[Bry5on]

Glad you've found those calcs helpful - I'd be happy to check out your modeling. Any idea what pages / what part of your build thread to aim for when searching??

Chassis stiffness is magical. I learned this from my Miata days. Interesting how much room for improvements exists on the M3 as well. Your M3 dampers are jacking down into the bump stops, have a TON of compression and rebound in the rear, and have ZERO high-frequency softening capability (which is what my Ripple Reducer provides, inspired by off-road racers who have been drilling small holes in their pistons for decades to filter road rumble). The behavior isn't unique to the E46 M3, but it's all to familiar when I look at sport sedans / sport coupes.

I would be happy to meet you in LA sometimes before I go if you want to experience first-hand what I consider a well-optimized GT / Dual-Purpose suspension (frequencies around 1.9 Hz / 2.1 Hz). I'd have the bulk of the drive so it's your call. I've had a lot of people decide to work with me without demo rides. Obioban / Ian has a setup from me on his E46 M3 and I'm doing to build one for his 128i that includes more recent enhancements to my Ripple Reducer per conversations and calculations with an Mech Engr customer.

The rain check would be driving to Alabama so I've got two weeks if we want to make a meet happen. I can drive during the week so it's not limited to weekends. Maybe sleep on it and see if this appeals to you?

Here’s the spreadsheet - for accuracy with roll and travel you’ll need to enter CG height as well as the corner weights. It seems a stock M3 is around 21” and a weight reduced track M3 might get as low as 19” based on the measurements I’ve seen so far. The sheet will also calculate new weight distribution numbers for added/removed mass in x, y, z coordinates. Some of the assumptions that simplified the model came from my 3D model of the suspension geometry, which I think is hyperlinked from the excel doc somewhere in there.

Im pretty busy with my day job (I’m also a mechanical engineer, mostly rockets, spacecraft and automotive body in white work to date) so I don’t think I’ll be able to coordinate anything within the next couple weeks but maybe heinzboehmer and or tlow98 can take you up on that as they’re local to you on the peninsula. They’re both also engineers with similar OCD and are quite familiar with my car and its various developments.

Personally I find 1.9/2.1Hz a little high for me but I’m open to new takes with more appropriate damping. Prior cars in the last two decades have had lots of custom suspensions (all pitch balanced, roll centers in the right place, I did my homework) and I usually find that for my daily driver I enjoy about the 1.6 Hz range. Any more than that and it seems to trend too far down the “GT3 daily driver” spectrum for me. My last 991 911 had an aftermarket controller on the sport PASM dampers which helped a lot during daily driving but ultimately I wished for a softer/longer spring even so. I think that car was up to 1.7/1.8 or so in the rear if memory serves?

In any case, excel sheet here: CG location change_332it.xlsx

[Suspension Decoder]

Nice to see you in here! Big fan of the spreadsheet you’ve been hosting for ride calcs. Thank you. If you’re interested, I’ve modeled roll, jacking and travel earlier in this thread as well.

I’ve been chasing chassis (vs suspension) stiffness and have roughly doubled the torsional rigidity of my e46 at this point. I’m actually pretty happy with the stock M3 ride frequencies and travel (my touring corner weighs very similar to an M3), just not in love with small bump sensitivity performance. The stiffness increases in the chassis have been super eye opening for grip, chassis and suspension/tire control. Next, if I can make the front struts act more like a constant cylinder than a wet noodle by redesigning the front knuckle, I figure I can set myself up to best position the dampers up for success by reducing some stiction and undamped flex.

I was actually pretty local to you for the past 8 years and only moved to San Diego two months ago. It would have been great to A/B drive both cars. Maybe I’ll come back to visit and can take a rain check.

Glad you've found those calcs helpful - I'd be happy to check out your modeling. Any idea what pages / what part of your build thread to aim for when searching??

Chassis stiffness is magical. I learned this from my Miata days. Interesting how much room for improvements exists on the M3 as well. Your M3 dampers are jacking down into the bump stops, have a TON of compression and rebound in the rear, and have ZERO high-frequency softening capability (which is what my Ripple Reducer provides, inspired by off-road racers who have been drilling small holes in their pistons for decades to filter road rumble). The behavior isn't unique to the E46 M3, but it's all to familiar when I look at sport sedans / sport coupes.

I would be happy to meet you in LA sometimes before I go if you want to experience first-hand what I consider a well-optimized GT / Dual-Purpose suspension (frequencies around 1.9 Hz / 2.1 Hz). I'd have the bulk of the drive so it's your call. I've had a lot of people decide to work with me without demo rides. Obioban / Ian has a setup from me on his E46 M3 and I'm doing to build one for his 128i that includes more recent enhancements to my Ripple Reducer per conversations and calculations with an Mech Engr customer.

The rain check would be driving to Alabama so I've got two weeks if we want to make a meet happen. I can drive during the week so it's not limited to weekends. Maybe sleep on it and see if this appeals to you?

[Bry5on]

Bry5on, greetings!

Our uber-moderator recommended I contact you. In a brief review of the first and last pages of your build thread, I can see you're extremely thorough. It also looks like you're in San Diego? I would love for you to experience a Fat Cat Motorsports suspension - I have the top-end Stage 3 Ultimate on my E46 330i right now (baby M3, not S54 swapped yet like your wagon, but lightened and tuned for track/autocross). The balance between grip and comfort is very good for a track/autocross-focused suspension.

I am leaving CA in a couple weeks for a relocation to Birmingham, AL, though would love to drive down (perhaps to LA?) and meet up with you! First, a phone chat would likely be a good start. My cell is 408-221-8247.

Cheers,
Jalal (Shaikh @ Fat Cat Motorsports)

Nice to see you in here! Big fan of the spreadsheet you’ve been hosting for ride calcs. Thank you. If you’re interested, I’ve modeled roll, jacking and travel earlier in this thread as well.

I’ve been chasing chassis (vs suspension) stiffness and have roughly doubled the torsional rigidity of my e46 at this point. I’m actually pretty happy with the stock M3 ride frequencies and travel (my touring corner weighs very similar to an M3), just not in love with small bump sensitivity performance. The stiffness increases in the chassis have been super eye opening for grip, chassis and suspension/tire control. Next, if I can make the front struts act more like a constant cylinder than a wet noodle by redesigning the front knuckle, I figure I can set myself up to best position the dampers up for success by reducing some stiction and undamped flex.

I was actually pretty local to you for the past 8 years and only moved to San Diego two months ago. It would have been great to A/B drive both cars. Maybe I’ll come back to visit and can take a rain check.

[Suspension Decoder]

Bry5on, greetings!

Our uber-moderator recommended I contact you. In a brief review of the first and last pages of your build thread, I can see you're extremely thorough. It also looks like you're in San Diego? I would love for you to experience a Fat Cat Motorsports suspension - I have the top-end Stage 3 Ultimate on my E46 330i right now (baby M3, not S54 swapped yet like your wagon, but lightened and tuned for track/autocross). The balance between grip and comfort is very good for a track/autocross-focused suspension.

I am leaving CA in a couple weeks for a relocation to Birmingham, AL, though would love to drive down (perhaps to LA?) and meet up with you! First, a phone chat would likely be a good start. My cell is 408-221-8247.

Cheers,
Jalal (Shaikh @ Fat Cat Motorsports)

[heinzboehmer]

The necking down is below the clamp, fortunately, so it’s not actually hurting deflection as that section is dormant. But good thought.

Oh right, was misremembering where the clamp went on the strut.

[Bry5on]

Looks like you're modeling this with a hollow cylinder of constant radii, but don't the dampers neck down at the knuckle interface?

I would think the necking down makes the deflection even more pronounced with just one clamp.

The necking down is below the clamp, fortunately, so it’s not actually hurting deflection as that section is dormant. But good thought.

[heinzboehmer]

Looks like you're modeling this with a hollow cylinder of constant radii, but don't the dampers neck down at the knuckle interface?

I would think the necking down makes the deflection even more pronounced with just one clamp.

[discoelk]

That stiffness increase almost justifies bracing the OE strut/knuckle interface.

[Bry5on]

Okay, did the math. George Hill came through and cut a strut tube open to measure its wall thickness. When accounting for the actual strut wall thickness, we get almost exactly a half degree of camber lost under the max-G load case.

And since this is a pretty simple beam flexing calculation, we can nondimensionalize (conservatively) the change of adding the second clamp 80mm higher. What's the result? It almost halves the expected deflection for any given load case on stock suspension, where the benefit is even greater the lower the car is.

So I'm planning to find a way to re-run another generative design iteration with the goal of keeping all the stiffness improvements but dropping some of the unnecessary weight imposed by the earlier iterations. More time in the design seat, coming right up.

[IamFODI]

Tough call, but...

My, not particularly well-informed, opinion is to go with the extra stiffness, on the basis that if you want to drop additional weight then there's probably still some other ways you could eke out some savings, but seems this is the only way to improve the strut mount stiffness.

^ This IMO

[karter16]

Looks like the only thing for it is an A/B test 😉

My, not particularly well-informed, opinion is to go with the extra stiffness, on the basis that if you want to drop additional weight then there's probably still some other ways you could eke out some savings, but seems this is the only way to improve the strut mount stiffness.

I was going to say you need to run the box section through the generative design tool to make it look more organic 😂, but then you posted the renders with the shielding etc. and it all ties together very nicely!

[YoitsTmac]

All fair points. I guess this points to why someone didn't just make the “perfect suspension” and never iterate. Pros and cons to each possible route you take.

- 1% weight, higher cost, less camber distortion, more consistent alignment under braking and turning
- easier dev, similar distortion to stock, but no really handling benefits outside of handling your updated control arm design.


The track guys seem pretty happy with the stock M3 geometry so I'm glad you're not messing it. I forgot one quality of Ackerman was its relation to the pivot point, so makes sense you can't adjust it too much. Definitely excited to see what you choose.


If you go for the more rigid setup, for prototyping, you can probably 3D print two pieces with some pegs to hold them together for initial prototyping.

[Bry5on]

What do you suspect the camber loss is? My initial inclination would be to say stiffen it up. But, for those who really want maximum performance out of these, you can get an alignment to contract these negative externalities.

Dropping a pound, while I don't know the percentage decrease from factory, should allow for more steering feel I'd presume. If you went this route, you could likely design the nuckle to “give more” performance IE Ackerman (maybe?) to offset the performance losses from lack of stiffness.

Of course, it's entirely up to you. Seems like the lighter design is also the easier build. Combined with your proposed CA design that makes the car more bump compliant, it feels like the more cohesive package. If the camber loss is similar to stock, then your net package will be an improvement over stock in weight, steering, bump compliance and maybe Ackerman.

You can basically interchange weight and rigidity as a benefit as the rest is the same. Otherwise strut flex can be adjusted for in an alignment while you can't align weight out of the system.

Yeah good points, I'm thinking about it similarly. One caveat: adjusting more static negative camber comes at the cost of braking performance. Camber loss looks like about .25 degrees in an absolute max-G corner with a sticky tire.

For percentage weight reduction:
245/40/17 tire: 25lb
17x9 apex wheel: 17lb
brakes: 28lb
e46 spindle, hub, heat shield: 15lb
damper: 8lb?
other stuff: 5lb? (control arm affective weight, spring effective weight, sway link, sway effective weight, etc
total: 98lbs

So 1lb is 1% of the front corner's sprung mass.

The stiffer part is also a bit more money, and it's taller than my plastic printer can print (time for an H2D??) so I can't do a full prototype unfortunately like the lightweight one.

I'm also maintaining the factory e46 M3 Ackerman setup as closely as possible. I adjusted the trailing arm pickup point along the virtual Ackerman line that intersects the car centerline at something like 400% of the wheelbase. In theory I can add a tiny bit of Ackerman before I run into the brake rotor, but not much. The newer cars use the dual ball joint trick to dial in more Ackerman while staying well away from the brake rotor. Since my car isn't lowered, I'm also not dropping the LCA and tie rod pickup points at all as the roll center height is pretty dialed in from the factory - not looking to change that.