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      02-12-2016, 07:07 AM   #1
KRZ3
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Body roll, stiffness and precision

@mods: could you move the thread to Chassis/Brakes/Suspensions please.

Hi everyone. I have a question for the chassis experts here, I'd appreciate some opinions.

Basically running stock chassis with EDC suspensions right now. I track 3-4 times a year and it seems to me the handling of the car could be improved especially by reducing body roll and increasing stiffness.
The question is: can I achieve this without changing OEM suspensions?

I am considering the following
a. upgrading the anti sway bars front and rear,
b. replacing the subframe bushings with solid ones,
c. putting monoball arms in the front.
d. I have considered replacing the entire sunroof with a much much lighter CF one to reduce the unusual weight at the top that doesn't help roll obviously, but I hit a wall with the missus...
e. I don't want to lower the car because I am running 295/35/18 in the rear and travelling heavy to holidays. I couldn't find stiffer springs that don't lower the car, and not even sure that's a good idea without having to change dampers. Suspension kits I don't want to go that route for now.

What I am trying to achieve is
1. Reduced body roll to allow harder cornering and faster recovery into straight line,
2. Better feeling, more clamped on, in the rear, in particular to get more precise feedback in tight corners from the tires when they reach their grip limits,
3. Higher precision in the steering wheel and slightly stiffer,
4. All of that without touching the suspensions, which I quite like on EDC Sport settings on track, comfort on family trip, and absolutey don't want to lower the car.

Would this make sense? What would be the pros and cons, in particular the overall balance of the car given stock suspensions but stiffer chassis components? Any risk on durability?
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Last edited by KRZ3; 02-12-2016 at 09:02 AM.
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      02-12-2016, 09:06 AM   #2
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a. upgrading the anti sway bars front and rear,
Will help with "body roll" but a proper coilover setup would be a better investment.


b. replacing the subframe bushings with solid ones,
This doesn't improve handling, just feedback.


c. putting monoball arms in the front.
Again, these would not improve handling whatsoever.


d. I have considered replacing the entire sunroof with a much much lighter CF one to reduce the unusual weight at the top that doesn't help roll obviously, but I hit a wall with the missus...
You're really suck with changing out the swaybars for a mild improvement, but if you really want to tune the handling to your preference, you'll want some coilovers with stiffer springs.
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      02-12-2016, 05:49 PM   #3
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Thanks doogee. Makes sense. Is there any drawback in upgrading just the sway bars?
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      02-12-2016, 05:52 PM   #4
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Quote:
Originally Posted by M//Watt View Post
Thanks doogee. Makes sense. Is there any drawback in upgrading just the sway bars?
Not at all! You'll definitely notice a difference. Get something adjustable.
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      02-12-2016, 06:01 PM   #5
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Ok great. I'll start with the adjustable bars then and work it up from there. Thanks.
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      02-12-2016, 09:09 PM   #6
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Only draw back is the rear sway bar is a bitch to re/re.
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      02-12-2016, 09:27 PM   #7
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I'd skip the rear sway bar. Most only do the front as the rear offers minimal benefit over stock and, as stated above, it's a lot of work to swap the rear.
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      02-13-2016, 05:11 AM   #8
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Don't most reaching drivers run with a softer rear anti roll bar than standard, or none at all. Arb reduces grip rather than increases I thought. More for feel again
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      02-13-2016, 05:17 AM   #9
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Yep:
http://iracing.wikidot.com/component...l-bar-sway-bar
Tuning advice
Quote:
Just like spring rate, you want to run as soft an ARB as possible while maintaining sufficient control of the car and body roll and the proper handling balance. Softer settings lead to more compliance and more grip on that end of the car. They also tend to be slower responding and easier to drive, but stiffer settings can be more stable and faster responding.
http://www.racedepartment.com/thread...ettings.39244/

Quote:
Anti-roll bar (front): ​

Use as stiff a roll bar as possible for good corner turn-in stability.​ (I would add "without affecting balance or compliance over bumps")

Anti-roll bar (rear): Use as soft a roll bar as possible for better traction under acceleration on exit

Last edited by crypticc; 02-13-2016 at 05:23 AM.
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      02-13-2016, 02:42 PM   #10
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Quote:
Originally Posted by crypticc View Post
Don't most reaching drivers run with a softer rear anti roll bar than standard, or none at all. Arb reduces grip rather than increases I thought. More for feel again
Very interesting but I am a bit confused here.

Quote:
If the bar is TOO soft, the car will exhibit exit OVERsteer. In this case, compared to a rear bar that is TOO stiff, the exit OVERsteer condition will be more gradual instead of a snap
How would a softer arb increase grip, it seems to defy physics?
Do many of us experience this in real driving vs theory only?
I am not sure it's easy to distinguish between snap and roll given the timeframe of the exit drift is so short.
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      02-13-2016, 03:49 PM   #11
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Quote:
Originally Posted by M//Watt View Post
How would a softer arb increase grip, it seems to defy physics?
Not a specialist, but if you think about extreme situation when the car has harder ARB it will lift the wheel, soft ARB leave the wheel on the ground and than you have more grip as two wheels are still in contact
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      02-13-2016, 10:22 PM   #12
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ARB = anti roll bar?

Generally...BMWs are a little backwards. You want a stiffer front bar relative to the rear. Some E46s run with no rear bar at all.

If you want to improve handling, get some slightly stiffer springs and front camber plates. The car will still roll but if you're only tracking 3-4x per year...not sure if it makes sense to get a super stiff coilover.

I had Dinan Stage 2 (springs+front bar) with GC camber plates. The car could keep up with almost anything in the corners except lightened race cars. It did have some trouble in fast switchbacks which is the only time you really feel the weight.
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      02-13-2016, 10:38 PM   #13
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The question is whether you want to materially increase your lap times. A good coilover setup will yield a 1.5-2 sec improvement on a 2 min road course. One of the weaknesses of the M3 is its tendency to understeer. Stiffening the front vs rear anti-roll bar will increase your mid-corner understeer, which is not a desirable trait. Stiffening the rear seems like a lot of work for marginal improvement.

Same concept applies to springs and camber plates...running softer front springs vs rear reduces understeer, running more front camber also reduces understeer. In my experience, the more understeer is reduced, the better the feel/confidence. Some body roll is not an undesirable characteristic as helps smooth transitions and helps put power down to the rear. The more you can get power down to the rear, the earlier you can get on the throttle. Especially with a low tq/high revving motor, corner exit speed is critical to improving lap times.

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      02-13-2016, 11:35 PM   #14
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Quote:
Originally Posted by FogCityM3 View Post
Stiffening the front vs rear anti-roll bar will increase your mid-corner understeer, which is not a desirable trait.
If you stiffen the front bar, you do get more mid-corner understeer if you are a perpetual late apex-er. Brake, turn in, coast and then throttle.

You do want to stiffen the front bar because you want more weight on the rear axle so you can put down more power and do what you should be doing in the E9X M3...steer it with the throttle.
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      02-15-2016, 06:13 PM   #15
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This is really useful guys, many thanks. I need to get my head around it to pin down what my rear snap exit really is due to and requires, but it sounds like I am going to go for the front sway bar and better rubbers than the PSS (they really feel greasy when hot chasing after 3 laps chasing the gt3 rs, I don't think they are that good for track) to start with, and see what happens.
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      02-16-2016, 05:36 PM   #16
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Point being, as I mentioned, you do want to maximize corner exit and get earlier on the throttle and not sure how much difference a sway bar adds to improving the rear squat/grip. TCKline is running stock engine with TCK D/A's with low spring rates ( 350f/600r - to maximize rear squat) and Hoosiers and NO front sway and getting 1:39 at Laguna Seca, and has set numerous lap records considering the light mods.

For aggressive driving through the twisties you cannot steer with the throttle as that would be far too aggressive for public roads. If doing aggressive street/canyon driving and occasional track time, no front sways but a good D/A system are probably the better route, given the higher cost will little benefit in terms of lap times and increasing understeer on the street (which IMO, is very undesirable given how often I go for spirited weekend driving).

Quote:
Originally Posted by bigjae1976 View Post
If you stiffen the front bar, you do get more mid-corner understeer if you are a perpetual late apex-er. Brake, turn in, coast and then throttle.

You do want to stiffen the front bar because you want more weight on the rear axle so you can put down more power and do what you should be doing in the E9X M3...steer it with the throttle.
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      03-02-2016, 01:06 PM   #17
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Have been going over this again, and considering 2 non-coilover options now. They are about the same price me think, probably around half the price of proper coilovers.

Option 1 mostly as above:
-front camber plates to be able to set to -2.0
-front H&R sway bar to reduce body roll
-rear solid subframe bushings to put down the torque from the blower
-rear toe arms to lock a slight pinch and calm the whole thing down on exit

Option 2
-TCKline E9x M3 EDC kit, which is a sleeve over with camber plates, and they let you choose spring rates while retaining EDC and stock height. They claim fastest lap times come with 350f:600r rates, I am thinking 400f:500r to further reduce front body roll, and keep more grip in the rear to account for the blower's torque.
http://www.tcklineracing.com/webdocs...Details760.cfm

What do you guys think? Pros and cons of either option vs the other?
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