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      10-08-2016, 02:53 PM   #1
wspohn
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Suspension Help Needed for Z4MC

Background: I am an old racer (since 1973) and have recently purchased a 2007 Z4MC. It doesn't require much, but I am minded to try and optimize handling, and am thinking about replacing the factory springs and shocks with BC Racing units, based on my previous experience with that product on other cars.

Problem: I see alignment specs ranging over 2-3 degrees of camber and from 0 to significant toe.

I will not be tracking this car, but do enjoy being able to drive briskly on winding roads and am posting to ask what specs people have found optimal for this model for occasionally aggressive street driving.

Note: specs from solo events are almost always incorrect for street use - usually wanting less front roll stiffness and different toe/camber. Track racing specs backed off a bit are more likely to be a good compromise for what I will be using the car for.
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      10-19-2016, 12:11 PM   #2
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Must be someone that has setup a car for the street for aggressive driving and has some info on what alignment work best and minimizes understeer. Anyone? Help.....
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      10-19-2016, 01:41 PM   #3
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are you going with camber plates on this setup?

FWIW;
I'm running a track setup with...
0 fr toe & 1/16 rear toe (total)
-2.9 fr camber & -2.2 rear camber.

For a nice street set up....
you can get to -2.2 fr camber by using a shim kit without upper camber plates
Fr toe depends on how you like the car to feel, I used to run zero toe evan when I wasn't tracking.

in the rear you could run a touch more toe if you want it to be a little less twitchy but that will also give you a little more understeer & tire wear.
Rear camber I would target in the -2.0 range

there are a few posts in this thread....
http://www.zpost.com/forums/showthread.php?t=545837
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Last edited by inTgr8r; 10-19-2016 at 01:46 PM..
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      10-19-2016, 01:44 PM   #4
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Quote:
Originally Posted by wspohn View Post
Must be someone that has setup a car for the street for aggressive driving and has some info on what alignment work best and minimizes understeer. Anyone? Help.....
There's nothing that I can say here that hasn't been already said.

Since you mentioned you're an old racer, you MUST know that all alignment settings are compromises between a bunch of parameters (comfort, wear, performance). Camber and toe are the only two adjustable parameters on this chassis, and without camber plates up front and camber arms in the rear you're beholden to the limited amount of adjustment that's available to this car. Meaning about 1º up front and rear in camber, and while toe settings are more adjustable, anything that veers from more than 1/16" either way is going to royally eff up your tire's usability.

As for what alignment "minimizes" understeer...Where is the understeer coming from? Corner entry? Corner exit? This chassis, in capable hands, is actually shockingly neutral. I once handed my keys to a semi-pro racer and after half a dozen laps, his comment was "wow this is the most neutral BMW I have ever driven." Granted I had 3.5º of negative camber up front, with 275 width tire all around.

I hesitate to give you any advice simply due to the vague way you presented your question. For a car that is not likely to see track? But plan to be driven "aggressively?" I'd minimize the rear camber (dial it to ZERO, or less than -1º depending on how "low" you get with your coil-overs) with slight toe-in (1/32-1/16" would do) and maximize front camber with same amount of slight toe-in (1/32-1/16"). Now, how much camber do you REALLY want or need is another question. With little to no camber in the rear, and a ton of camber up front, you may potentially see mid corner to corner exit oversteer, which, IMO, is the preferred set-up for "aggressive" street driving. Granted, not knowing how low you'll end up, that front camber can be as little as -1.5 to -1.7º, to as much as -2 to 2.5º. To get to desired effect, you'd "ideally" want 2x the camber up front compared to the rear on this chassis if you continue to run staggered sizes, or 1.5x up front to the rear ratio if you managed to square it up.

Otherwise, you can go MY route. -3.5º up front and -2º rear. Combined with some "aggressive" driving you'll likely be paying for a new set of tires every 6 months or 5,000 miles, whichever comes first, on THAT setting.
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      10-19-2016, 02:42 PM   #5
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Thanks, guys. I'll bear all that in mind when I do my first set up.

I will not be lowering the car - it is already low enough in terms of the roads around here.

Why is it that many things people want to do to (at least in their eyes) enhance appearance, screw up the handling? I've driven other people's cars that have overly large wheels and higher than stock unsprung weight, as well as some cars (depending on suspension) that suffered bump steer due to lowering, not to mention bottoming out routinely.

Oh well.
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      10-19-2016, 03:50 PM   #6
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Quote:
Originally Posted by wspohn View Post
Why is it that many things people want to do to (at least in their eyes) enhance appearance, screw up the handling? I've driven other people's cars that have overly large wheels and higher than stock unsprung weight, as well as some cars (depending on suspension) that suffered bump steer due to lowering, not to mention bottoming out routinely.
Because most people don't know what they're doing.
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      10-19-2016, 09:26 PM   #7
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If you guys saw how much westend (a reputable suspension company for track cars) raised my car.
Looks so ugly that I try to not look at my car anymore, but car has loooot more grip on high speed turns now.
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