Black & Tan 332iT

[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.