Black & Tan 332iT

[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.

[YoitsTmac]

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.

[Bry5on]

Okay, so I have a dilemma. I got back to work on the custom suspension knuckles. As a reminder, I'm targeting the non-m steering ratio, the later model replaceable beefy wheel bearings and a stiffer overall knuckle. Ideally, we do all that with an unsprung weight reduction.

I'd been pursuing 3D printed aluminum, but was juuust shy of making the loads close with the safety factor I wanted. Then I remembered that even 3D printed materials can be heat treated for better properties. Once I punched those properties in to my analysis, the loads closed with some margin. So we're back in the game, after receiving the printed parts I'll just need to do a multi-hour ~450C oven heat treat followed by a quench, then a handful of hours at 100-150C for accelerated aging. The e39/porsche style steel inserts still need to be very strong, 4340 for those.

So back to the dilemma. I've been hemming and hawing about putting a second strut mount up above the first one ever since I saw the amount of camber loss that happens from strut bending (the primary source of camber loss, as it appears). I decided to take some inspiration from the M4 GTS, but figured I could do better by using 3D printing. The F80 M4 GTS knuckle:


This knuckle uses a second strut clamp and some ribs to connect directly back to the wheel bearing. So how can we do better? Well, because we're going to be 3D printing these, we can leave internal voids in places that would never be able to be machined and we can box this entire section out. This should significantly stiffen/support the strut which will provide less hard corner camber loss and also better damper motion (because it's not actively being bent nearly as much). BUT it adds 1lb to each corner, which means I'll effectively come in at the same weight as the stock e46 M3 knuckle, whereas before I was dropping a pound. So what do you all think I should do here, lightweight or stiff?


edit: Here are the heat shield options as well. One simple, one ducted. And as you can see, the gusset acts as the heat shield to protect the strut from radiation:

[Bry5on]

Short on time so the rest of the updates will have to wait. But in the meantime, the Tesla Model X hitch adapter will fit the BMW receiver if it is 1) bored out a little in the aluminum section and 2) clearanced a little bit where the blue is in the photo below. Party time, doing our family e39 touring this way.




3D scan, Tesla hitch: https://s.digital3dcloud.com/space/f...lang=en&loop=1

3D scan, BMW hitch: https://s.digital3dcloud.com/space/f...lang=en&loop=1

Preview, remember this project?

[Bry5on]

What is your cutoff like? I had been strongly considering NHK retrofits for my sedan but this is the first bad review i've heard.

These specifically, which seem to offer a pretty level cut:

https://sfbay.craigslist.org/sby/pts/d/santa-clara-bi-led-headlights-for-bmw/7822160299.html

Yep, that’s the cutoff from about 5-10 feet away. As you gain distance, the cutoff looks more and more extreme. It’s hard to describe, as it’s not as obvious or bothersome statically on a perfectly flat road, but as you accelerate/decelerate or go through undulations, you’re very aware of the cutoff. I guess you could say it’s distracting. I’ll keep tweaking to see if I can find a perfect height setting, but no luck so far

[Kevin]

What is your cutoff like? I had been strongly considering NHK retrofits for my sedan but this is the first bad review i've heard.

These specifically, which seem to offer a pretty level cut:

https://sfbay.craigslist.org/sby/pts/d/santa-clara-bi-led-headlights-for-bmw/7822160299.html

[IamFODI]

I’m not exactly a headlight expert, but glare might be the right word to describe it. They’re so damn bright, but the brightness is a little jarring, especially when combined with the cutoff that you CANNOT get into a good spot. The light coming off of reflective signs is very intense, and generally the light coming off of other objects is also intense. I tried a few level adjustments and either you’re blinding cars in front of you, or the cutoff is dropping into the road because of the height of the step in the cutoff. They’d be worlds better if the cutoff was just flat.

My wife’s and my prior Porsches both have/had LED headlights and didn’t experience either of these issues, so I was unpleasantly surprised. These are just as bright, if not brighter, but the execution isn’t fantastic.

I'm no headlight expert either, but the experience you described of light from reflective signs and other objects is what I understand glare means. That was exactly my experience with high color temp headlights. If I ever found myself on an empty highway at night and flicked on my high beams, a good sized sign would be hard to see past.

Not surprised that Porsche's OE headlights mitigate these issues. I'm sure that's an example of the benefits of something that's engineered more-or-less as a whole from the ground up. Higher color temps will always cause more glare and eyestrain, all else equal – but I'm sure managing the beam pattern can do a lot to compensate.