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11-11-2013, 07:54 PM | #23 | |
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i took the car to pocono raceway and had an awful time. afraid to make any aggressive steering input and sognificant body weight shifts at high speed...I activated DSC at 130mph on the bending straight. terrifying the car already has limiters in it, I suppose replacing rtabs would be a first check before doing anything else. my last mz4 which I wrecked (sold on copart recently) was perfectly sorted and I was doing ~125mph uphill esses at VIR. I'm afraid I'd be weary of doing even 100in this car the way things are atm :/
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11-11-2013, 08:25 PM | #24 |
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For me I am more concerned about body roll. Now that I have coilovers with as stiff springs as I am prepared to put on a car that sees street duty (a mere 500lbF, 600lbR) I have not seen much of a reduction in roll. Some, but not enough. I hope to tune this out with the stiffer front sway bar. Today I ordered the same TMS set linked by the OP. It's not much more expensive to get front and rear as opposed to getting just the front, so I will try with both, and then disconnect the rear and see which setup I prefer.
The pics below (on stock suspension and stock ride height) show what I feel is too much roll. There is about 3.5" of difference between the loaded unloaded sides. I'd like to see more like 1.5". I'll post back in early December once tested on the track. Hopefully I am as happy with the change as the OP! After that I'll look at RTAB/L's.
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2006 IBlue BMW Z4 MC - ESS VT2-525 Supercharged, JRZ RS1 suspension (500#F, 600#R) with Vorshlag plates, ST Trophy BBK with CL R6E pads, KKS gated exhaust, TMS sway bars, RE rear camber arms, VT engine mounts, Recaro Pole Position (driver), APR GT wing, Street: Volk G2s and Potenza, Track: Volk TE37SLs and BFG R1s.
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11-11-2013, 09:00 PM | #25 | |
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You need body roll in order to transfer weight and get power down. If you make the car too stiff, you'll end up reducing grip |
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11-11-2013, 09:14 PM | #26 |
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Yes but body roll also transfers weight to the outside, increasing the load to those outer tires and pushing the center of gravity further to the side. Also the resultant inertia from a rapid and excessive shift in CG such as on a chicane or even just on a single corner can upset the car. Plus it reduces the cars ability to apply optimal camber.
There is an optimum amount of roll specific to each car/driver/track. And for me at least, the Z4M's bias is too far towards roll. I totally agree with your comments on "too stiff", but surely we don't need to argue the benefits of keeping a car flat through a corner?
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2006 IBlue BMW Z4 MC - ESS VT2-525 Supercharged, JRZ RS1 suspension (500#F, 600#R) with Vorshlag plates, ST Trophy BBK with CL R6E pads, KKS gated exhaust, TMS sway bars, RE rear camber arms, VT engine mounts, Recaro Pole Position (driver), APR GT wing, Street: Volk G2s and Potenza, Track: Volk TE37SLs and BFG R1s.
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11-12-2013, 05:55 AM | #27 |
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The stiffness of the bars changes the RATE of weight transfer. If the roll centers aren't migrating too far during roll, the amount of weight transfer is identical regardless of bar. Very stiff bars will transfer the weight "instantly" causing a car to feel twitchy. There's no time to perceive the change in grip. Soft springs and soft bars allows the car time to communicate what it's doing to the driver. Obviously we don't want to wait too long!
The difference in driving pace and the driver changes what is "optimal" roll stiffness. A fast road course and an autocross are very different situations. Another point is that your fancy coil over suspensions (with all those knobs) are designed to use the displacement in roll at each wheel to control the rate of weight transfer individually via the ratio of compression to rebound . Then again... "Any suspension will work if you don't let it." Extra points if you know who's quote it is! |
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11-12-2013, 08:00 PM | #28 |
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Lots of good input here, I just want to add that after an entire day of mountain driving my car feels more neutral than ever and my confidence is greatly improved. The car communicates so much more now, before when you push the car it would understeer on entry and then try to oversteer on exit. DSC would kick on all the time and now hardly ever and, when it does, the intervention only lasts a split second. I am on stock suspension and have decided to keep my stock springs but, will install Bilstein HD shocks on a week or so and report back. From all reading I've done the OEM shocks deteriorate rapidly and weren't great to begin with. New OEM RTAB with limiters will be installed at the same time.
I personally don't feel there is enough gain to be had from adjustable coilovers to warrant the cost and aggravation. Not to mention the constant horrible ride from the stiff spring rates, noise, rattles, squeaks, and a ride height that makes driving the car anywhere other that a track impossible.
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11-13-2013, 10:20 AM | #29 | |
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11-13-2013, 01:24 PM | #30 | |
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11-13-2013, 03:53 PM | #31 |
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11-24-2013, 07:42 PM | #32 |
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I got the TMS bar for my Z4MR a month ago and I love it. To me this is a no brainer mod for the money, the steering feels better when going over rought surface and turning. Looks good too, if you care about looks. Highly recommended.
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