Black & Tan 332iT

[Bry5on]

New feature, because everyone needs more math in their life!

It occurred to me that since I've got suspension geometry and center of mass information, I could now add jacking force calculations to get a true representation of suspension travel (jacking is basically the geometry forcing the body upwards during lateral cornering). This led me to a cool realization! The reason BMW uses an inboard spring is probably all about minimizing jacking travel! Jacking is a force internal to the car, so it acts at the spring rate, where your suspension normally acts on the tires, a force external to the car, so it acts at the spring rate *and* motion ratio. BMW chose to have a high rear roll center for suspension dynamics, and this means that there's a lot of jacking force. To minimize the effects of jacking, you need a stiff spring rate. If BMW had put the spring over the shock with a similar ride frequency (probably the easiest thing to do honestly) then the car would rise about twice as much in the rear during cornering, totally jacking up (pun intended) your rear camber! With the spring in the location the factory chose, it turns out the math shows how little rear compression is used in corners. Most of the rear roll comes from the inner side of the rear lifting in a corner! The front is different, jacking forces are low due to the roll center being just above the ground.

So, PSA: Don't run rear coilovers unless you 1) really know what you're doing and 2) are running super stiff springs (because you have aero is the only real excuse)
Also, PSA: Don't lower the front of your car unless you 1) really know what you're doing and 2) are running super stiff springs and/or sways

In any case, my fancy suspension spreadsheet will calculate jacking forces and suspension travel for various G-loads in corners. Take a peek at the travel numbers for front vs rear and inner vs outer below:


CG location change_332it.xlsx

[Bry5on]

Ah, didn't realize you did the roof rails, as well, you animal. Can it be done without removing the headliner? Big weight savings!

And my back-of-the-napkin says a George Hill carbon roof might drop the same amount in weight and not quite as much CG. Sounds lovely.

Yeah, super easy to remove, all from the top side. I think it looks more appropriate with the rack but I’ll take the weight savings any day!

Things would have to get rather serious to consider a carbon roof - that juice doesn’t quite seem worth the squeeze unless the whole car is going under for a respray and/or fenders.

[tlow98]

Ah, didn't realize you did the roof rails, as well, you animal. Can it be done without removing the headliner? Big weight savings!

And my back-of-the-napkin says a George Hill carbon roof might drop the same amount in weight and not quite as much CG. Sounds lovely.

[Bry5on]

And now the roof is naked. The rack setup ended up weighing 49lbs and removing it dropped the CG height by a half inch.

[tlow98]

That paint job 😋. Tasty!

[Bry5on]

So we're not done with yesterday just yet. After I was free and clear, I headed to the machine shop to knock another thing off my list, because while I was working on the vincebar, my mtech-2 bumper insert with trailer hitch cutout showed up. You can see where this is going.

We're trying to make this here: Onshape

I started with a scrap block of aluminum and cut it roughly to size:


Then migrated my way over to the Bridgeport to start taking shape. First removed a bunch of material to create a clevis:


Then flipped it over and drilled/power-tapped the hole pattern to mate to the euro tow bar (plus a test fit):


Then I flipped it on its side and drilled two 5/8" holes all the way through both sides of the clevis so that it can bolt directly to the adapter used in Stealth Hitch kits (same system we have on the Macan) like this:


After a quick deburr and clean, assembled it all together, threw it in the trunk of the jag and went home:


And that brings us to this morning, where things get exciting between coats of paint on the vincebar. I popped the bumper off, removed the standard mtech-2 bumper insert, trimmed a section of the bumper beam, removed the bumper shocks and installed the hitch. It fit like a glove with just enough room to comfortably actuate the hand lever of the Stealth Hitches adapter:


And here it is in all its glory, no additional trimming required, great placement, centered with plenty of driveway clearance:


And that's it for the hitch install! The factory setup was rated for over 4,000lb of towing capacity but only 165lb of tongue load. Not a problem for me since I'm planning to use this to hold two mountain bikes on a 1up rack, which will total about 120lbs. This 2" receiver is totally removable and can be detached and hidden in about 30 seconds.

It's worth noting that this is the factory BMW version of the hitch, made for BMW by Westfalia, and different from the Westfalia version available today because this one is aluminum and about half the weight. Of course I weighed everything, and after subtracting out the 8lb weight of the bumper shocks, I've added just 18lb to the rear of the car, vs 55+ of the roof rack setup. Once the rack comes off, I'll come in at ~3440lb and 49.4/50.6% weight distribution with a half tank, which is almost dead on for a stock e46 M3. Pleased with this outcome once again!

I'll drive the car tomorrow after a full 48 hours of epoxy curing, but for these two, no noticeable change is best.

[Bry5on]

Alright, here come even more pictures to make this thread take longer to load.

Yesterday was a big enough day that I had to drive the other car all weekend:


We had some contractors over, and I was stuck at home 'just in case' so you all know what that means. It started off with finally taking the plunge on cutting out a section of my trunk floor to install the stealth vincebar. Tourings must use the stealth version to make sure all the extra flooring clears and can still be bolted down onto the existing studs. I masked the car off and had a go with the cutoff wheel..


I'd already drilled and tapped through for the vincebar while I did the subframe previously, so once the cutting was done, I took to flattening the "T" stiffener in the floor with a combination of chisels and drifts. It flattened out fine, and where it depressed lower than the floor level, I made sure to add some extra epoxy so we're all fine. So, flattening, grinding, and drilling for rivets:


Then we bond prep for the Teroson EP 5055 structural epoxy, I bonded the full length of the bar to capitalize on as much stiffness as I can get from this thing:


And install and prep for paint:


Then after 24 hours of curing today I added a little bit of knead-epoxy underneath the studs to give the trunk floor some support and hit it with a coat of paint. BAM look at that:


Also, while I was in the garage, I replaced the damn exhaust cam sensor o-ring that'd developed a leak I could smell from inside the cabin:


And that rounds out the vincebar. Second post coming in hot.

[0-60motorsports]

Yeah, I'd recommend just the one limiter on the outer side, especially if you want to run CSL or CSL-like rear toe settings. Adding an inner limiter would prevent the bushings from toeing in under braking, which aids in stability, and in reality would cause a slight toe-out under braking due to the angle of the RTAB. With the limiter on just the outside, you get a very slight toe-in under throttle, and a more significant toe-in under braking. It's perfect

The Z4 RTABs will function like the OEM M3 ones when hitting bumps, but should hold alignment a bit better and be more stable under throttle when combined with the limiters vs OEM M3 bushings.

Awesome, sounds good. I'll have the inner limiters removed next time the cars on he lift for any job. Thank you.

[Bry5on]

I also finally did the same a year or wo back, OE M3 RTABs with Limiters, do you recommend the one sided limiter system? Any harm in having them in both sides?

Yeah, I'd recommend just the one limiter on the outer side, especially if you want to run CSL or CSL-like rear toe settings. Adding an inner limiter would prevent the bushings from toeing in under braking, which aids in stability, and in reality would cause a slight toe-out under braking due to the angle of the RTAB. With the limiter on just the outside, you get a very slight toe-in under throttle, and a more significant toe-in under braking. It's perfect

The Z4 RTABs will function like the OEM M3 ones when hitting bumps, but should hold alignment a bit better and be more stable under throttle when combined with the limiters vs OEM M3 bushings.

[0-60motorsports]

I also finally did the same a year or wo back, OE M3 RTABs with Limiters, do you recommend the one sided limiter system? Any harm in having them in both sides?

[Bry5on]

Well gents, I’ve finally got it. This morning, I did e89 Z4 RTABs with outer side limiters along with the 1mm larger CSL rear sway bar. Man, this is the hot ticket. I’ve finally got it right! That little bit of extra rear roll stiffness made all the difference. The car is more neutral and playful in corners now, super neutral and fast if you’re smooth, but it’ll still understeer on entry and oversteer on exit if you’re ham fisted/footed. Really nice to have that little bit of extra roll stiffness for the square tires on stock M3 springs, and it still has juuust a touch of understeer balance. The math says this should be keeping me off the bump stops and I’m inclined to agree. Just perfect, very happy over here.

What can I say about the Z4 RTABs? Well to my taste, they’re 75% of the precision of solid bushings, with the same NVH as stock bushings. No more rear end wiggling on throttle, but no NVH penalty. Really fantastic trade off as the rear is very well controlled again. The reason to go with Z4 bushings is all about how much rubber they have to press against the carrier (or limiter in my case). Otherwise they’re the same internal stiffness and geometry as stock e46 M3.

The bushings that came out of my car are near as new M3 parts, lemfoerder if memory serves, and had just a few thousand miles on them. You can see below that there’s plenty of evidence of the bushings toeing out all the way to the edge of the carrier. This calculates To almost a full degree of toe out. Hugely destabilizing! Again, these are new bushings! A solution to the rear end wiggling under throttle was required.


I used limiters from ECS for the outside of the Z4 bushings (half of the kit of four), which have a much bigger rubber lip on the outer side (toe out under throttle side). To fit the limiters, there’s just a minor trimming operation needed to make the limiter sit totally flush with the bushing. They then get installed all the way until the flanges touch the rear trailing arm. They get bottomed out, which looks a bit off, because the metal is not centered in the bushing like the e46 style, but this will place the bushing in the correct location.
By only installing outer limiters, this mitigates toe out under throttle while maintaining the factory designed toe in under braking for braking stability. I really wanted to keep that feature, and I’m happy to report that the results are great.
Other than that, install is totally normal. Make sure you set your toe correctly after or have the car realigned. Here are a bunch of pictures that might come in handy if you’re doing this yourself, including my method for keeping my alignment the same before/after.


And a few shots of the CSL rear bar going in, along with the final installed washer fluid reservoir for good measure. Happy Saturday.

[Bry5on]

Snuck a couple hours in to make the wagon that little bit more M3-like. In prep for the v-brace bracket welding, I installed M3 undertray panels with non-m sedan deflectors in front of the rear tires. I’m happy to report that the M and non-m parts fit perfectly together to support the v-brace while also mating up to the sedan side skirts.


After I got through that, I installed the M3 washer fluid reservoir and ran the wires to the level sensor. I’m waiting for a 5/32” union fitting before I plumb in the hydraulics and switch my wiring to the M3 pump. To fit the reservoir to the bumper carrier, I had to relocate the horn to just under the right side grille as the horn and washer reservoir were occupying the same space.
I may be the only e46 with two washer fluid reservoirs right now.

That’s all for today

[Bry5on]

And now ... we bring it all together. With the suspension modeled in CAD, all the car's measurements, and the known roll stiffness of the suspension setup, we can now calculate travel at the wheels (I'm approximating this within a few percent to keep the math simple) to make sure there's still some travel left and the car won't be on the bump stops. As far as I can tell, the factory setup was about 1/8" off the bump stops at 1G steady state, which seems about what I'd have expected. Maybe my math is off somewhere and cobra can validate my travel calcs . In any case, here's how my setup stacks up with stock M3 suspension (.90" @ 1G):


And with some additional sway bar stiffness (.78" @ 1G):


And to see what happens when we raise or lower the car..

[Bry5on]

Yeah. Bry5on let’s play. There’s only one catch. I’ll only take them if they’re hand painted.

You’re in luck! There’s a town about three miles back that way. I’m sure you’ll find a couple guys there.

Come on by, make a list so we don’t forget anything. I still have your 14mm Allen key and I’ve also got multiple thicknesses of spring pads if you like the Dinan springs and want more suspension travel (or the high roll center

[tlow98]

I regret not doing camber arms last time I had my subframe out. Might be worth to just do them now before you assemble the sedan.

Yeah. Bry5on let’s play. There’s only one catch. I’ll only take them if they’re hand painted.