UPDATE
So far, I've fitted the AC Schnitzer Racing suspension, a StrongStrut front strutbrace and 10mm spacers all round, and found what I consider to be the near-optimum damper settings for fast road use. IMO, I consider it much harder to find the optimum "fast-road" settings rather than "track" settings because the quality of our road surfaces varies so much, from track-like motorways and dual carriageways, to pot-holed, undulating, heavily-cambered minor roads with all grades between. Likewise, when lowering the car it is important to ensure that the car retains sufficient ground clearance so that you can go anywhere without forever worrying about doing damage to the car if it's too low. Fortunately, I've been through the suspension upgrade experience with my Z3MC, so with the suspension upgrade to the Z4MC, I've known precisely what I want to achieve from the outset and that it is actually attainable, and that I know what hardware changes I need and what adjustments to make to achieve my goal.
I've learned that with adjustable suspension, it's better to have the dampers set slightly too soft rather than slightly too firm so that the car will handle and ride well on the worst of roads that I drive on and not on just 90% of them and one of my two major criticisms of the OEM suspension is that the rear suspension is just too firm, which makes the car a bad ride/handling on at least 20% of the roads that I drive on. I believed that over the past few weeks since I installed the ACS suspension, from test driving, I'd found my optimum damper settings with the right front/rear balance which should account for 100% of road surfaces.
When I bought the car four months ago, the OEM geometry of the car showed toe-in on both front and rear axles and more negative camber on the rear axle than at the front. Lowering a car increase negative camber and toe-in, so this needed to be corrected. Also, with stiffer front springs than OEM, lateral bodyroll is somewhat reduced, so the need for large camber and toe angles is reduced because the dynamic geometry remains closer to the static settings. Adjusting the geometry isn't rocket science if you know which parts you need to adjust but you do need to follow a careful method so that you retain a 0 thrust angle to keep the car driving straight and true, and that you properly measure the changes you make. I've now set up the car with 0 degs toe all round, -1.3 degs camber at the front and < -1 degs camber at the rear. The car is 10mm lower at the rear and 15mm lower at the front.
I took the Z4MC to the Zedfest at the Silverstone Classic event yesterday and this was an ideal opportunity for me to assess my suspension upgrades because my route was a 70 mile trans-Cotswold route on the twisties (140 miles in all), on dry roads. I have to say that the ride is now absolutely perfect for me: I had absolutely no uncomfortableness whilst driving, nor any post-driving stiffness at all, as I did when I made the same journey 2 months ago. This means that I have the rear damper setting just right.
The second major problem that I have with the OEM suspension is that the front end was too soft which caused lifting on acceleration which made the steering imprecise and floaty, with pitching under braking leading to understeer. Yesterday, I had ample opportunity to test the front end with lots of overtaking which means crossing the camber of the road twice when completing an overtaking manoeuvre: I found that the front end lifting/pitching was minimal, which made the steering very precise, even accelerating hard on bumpy and undulating surfaces on relatively narrow roads. I think that I might be able to slightly stiffen the front damper settings if I were to stop with the upgrades at this point, but I have an H&R 30mm ARB to fit, which will probably do the trick, so I'll refrain from making any further adjustments until that is fitted. I also have a TMS limiter kit to fit on the rear trailing arm brackets, which I expect will also make the good even better.
I have always been amazed at how most other Z4MC owners can tolerate the OEM suspension because it is truly awful. I have experience of KWV3 (with a front coilover damper akin to Clubsport) on my Z3MC and now the AC Schnitzer Racing suspension on my Z4MC and I can highly recommend both suspensions to anyone. For me, upgrading the suspension to a decent adjustable set-up is far and away the best money of all that you can spend on your car. Setting up adjustable suspension is NOT a black art, it's just a logical sequence to follow and if you are happy to change your brake discs and pads yourself, then I consider changing the suspension and setting it up yourself is at the same level of difficulty although it might take a bit longer to do.
The ACS Racing suspension is much easier to adjust than the KWV3 but if you do want to go on track, it is well worth making adjustments from "fast-road" settings to pretty stiff track settings, because this really improves the handling some more on smooth surfaced tracks. IMO with adjustable suspension you can have the best of both worlds rather than have to suffer a "one size fits all" compromise.
these things are run with proper slick tyres are are putting way more stress than my road tyres/slicks can ever muster.... its a non issue ;-) the contact patch is more than adequate, to see them installed with them wheel on, you'd understand what i mean!...
