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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Mon, Sep-25-2017, 01:05:16 PM   #1
Fissionx
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Default Suspension setup and sudden snap oversteer

Hello

I am having snap oversteer issues after making some changes. Purchased car 3 months ago and still resolving issues. There is no way in HELL I am putting this car on track (was scheduled for this weekend) in it's current state.

Front is stiff and very very darty - meaning very sensitive to steering inputs resulting in change in direction faster than any M3 i've driven before. BUT Toe (see below) looks fine....?
Rear is stiff and very very loose. Once the car even starts to rotate the rear is gone and not coming back. When it develops enough rotational inertia for one to really notice it's too late, no amount of steering input or light throttle will save it; you're up in smoke pointed the wrong way. You have to be expecting it to snap (not ROTATE, but SNAP) then MAYBE you can catch it before it even hints at any sort of rotation.

Current Setup:

05 M3 170kmiles
used ST XTA Coilover suspension (~450/550 lb/in springs is my guess from what i've seen).
Dampening 1/2 turn from full stiff both sides.
Powerflex FCA
Powerflex RTABs
Adjustable rear camber arms
13.2"/12.8" Front/Rear height
Alignment:
-1.8* camber, 7.8 caster, 0toe front
-1.2* camber, 1/8 toe rear in
225/255 stock size tires 19s

Recent changes
The car was purchased without front subframe reinforcement plate (the metal 'skid plate' - it was missing) and I just put this and the rear V-brace back on with no other changes; now I am noticing these issues. Alignment was one week ago= and did not notice this as much then. I have not check alignment after installing the front subframe reinforcement plate but that was a simple bolt-on. It sure as hell made the car stiffer and now this oversteer issue is much worse.

DISCLAMER- have 10+ track events, owned M3s before, owned/tracked and setup Porsche 911 (996), driven GT3s etc. Snap overseer is worse than 911s I've owned/driven terms of it's rapid onset and inability to control once it's gone. Something is not right. It happens on turn in (slow turn-in, no trail braking), and with gradual application of power on exit.

Thanks
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Dan - 2005 BMW M3 SMG 170km stock

Last edited by Fissionx; Tue, Sep-26-2017 at 04:30:28 PM.
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Old Mon, Sep-25-2017, 01:19:01 PM   #2
Fissionx
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Default Re: Suspension setup and sudden snap oversteer

Tires are shitty compound and old as hell but still plenty of tread left. I have some newer (used) PS2s to put on 235/255 19s. I don't THINK this will solve the issue, but I will see. Will be installed today or tomorrow.

Otherwise I will re-check alignment, play with dampening more and try to dial this out as much as possible but I feel like something is off. If reasonable adjustments can't dial it out, I'll bite the bullet and get a new TC Kline setup or BC Racing setup. Then I'm not sure, give up or deal with it or bigger tires rear or what.

Anyways what can I do or check right now...
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Old Mon, Sep-25-2017, 01:53:45 PM   #3
CrookedCommie
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Default Re: Suspension setup and sudden snap oversteer

What's your sway bar settings at?
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Old Mon, Sep-25-2017, 04:24:42 PM   #4
mrgizmo04
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Default Re: Suspension setup and sudden snap oversteer

Did you get alignment after installing the front reinforcement plate? 2 of the bolts go through the control arms, so that will definitely impact geometry by preventing additional movement/flex. It is normally not advised to drive the car without the front reinforcement plate. Rear v brace does not have impact on rear geometry.


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All DIY: 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, WPC rod bearings, Beyer driveshaft, full SS (SS stepped V1, catted S1, resonated S2, SS sport), Sachs clutch/flywheel, rear main, VANOS bullet proofing with anti-rattle, valve adjustment, cooling refresh, Ohlins R&T/Swift 448f 672r/GC street tops and camber plates, AFD E85 Proflex kit.

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Old Mon, Sep-25-2017, 05:40:38 PM   #5
Fissionx
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Default Re: Suspension setup and sudden snap oversteer

No alignment after installing reinforcement plate. Dammit I'm sick of this sh1t! This will be my 3rd alignment this month....
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Last edited by Fissionx; Mon, Sep-25-2017 at 06:04:35 PM.
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Old Mon, Sep-25-2017, 05:59:35 PM   #6
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Default Re: Suspension setup and sudden snap oversteer

Depending on how sticky of a tire you are planning on running, you may want more front camber as well.
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Old Mon, Sep-25-2017, 06:11:28 PM   #7
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Default Re: Suspension setup and sudden snap oversteer

Quote:
Originally Posted by CrookedCommie View Post
Depending on how sticky of a tire you are planning on running, you may want more front camber as well.
That was going to be my input - your front camber should be about -1* more negative than the rear

The reinforcement plate isn't going to significantly screw up your alignment at all. If you're experiencing something dramatically "off" it's not going to be from something like that

Also, where are you getting your car aligned? I've had bad luck with all but a few shops "fudging" alignments
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Old Mon, Sep-25-2017, 06:25:03 PM   #8
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Default Re: Suspension setup and sudden snap oversteer

How much faith do you have in the accuracy of the alignment measurements?
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Old Mon, Sep-25-2017, 06:38:40 PM   #9
Fissionx
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Default Re: Suspension setup and sudden snap oversteer

They are a track oriented BMW shop. As good as any around. I'll ask to see if they can throw the car on the racks and check where it's at.

Sorry maybe this wasn't clear in my first post. Tires to be installed are Michelin Pilot Super Sports 235/255. Right now they are some old shitty tires.

Toe has definitely changed from installing these plates. I think resolving that will fix steering and putting on the tires will help, however some of this may also be due to the suspension and dampening or just 'par for the course'. I haven't been on track in 5 years if that matters. I am emerging from a long stint of car apathy.

I suppose my question is also:
How much do these cars have a tendency to snap on slow speed (no trail braking) entry, or even exit?
- My last M3 the rear was very stable and so hard to get out the understeer. Great on the street, borderline boring on track. I wanted to develop more as a driver sold it for 911.
- The 911 was much more lively but still allowed more slip and rotation before a rapid decline in traction. Feel, feedback and driving pleasure blew the m3 away. M3 superior in other areas like driveability streetability every day easy and room, etc. With the 911 I hated the attention and stigma. Paid 18k people always thought I spent 100+
- This setup now just falls off a cliff with no warning - snaps around. Car was a great deal less than 11k in it thus far
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Last edited by Fissionx; Mon, Sep-25-2017 at 06:51:59 PM.
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Old Mon, Sep-25-2017, 06:49:51 PM   #10
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Default Re: Suspension setup and sudden snap oversteer

Five ideas, with the caveat that my experience is grounded in the E36:
  1. Check your ride heights front and rear. You should have the rear a smidge lower than the front, ~3/4" is the E36 sweet spot. This looks funky to the hardparker crowd but their input on track stuff is invalid.
  2. You have surprisingly little rear camber, and not much front camber either. See about increasing the rear camber closer to -1.8 or -2.
  3. Is your diff functional? I was getting crazy power on oversteer once the inside tire was unweighting and it was due to the clutches in my diff had worn to the point of not functioning.
  4. If you have aftermarket sways, how do you have them set?
  5. Have you had the car corner balanced? If not, have a track focused shop corner balance and adjust ride heights at the same time.

For reference, I have an E36 with MCS DA set around the middle for rebound and compression, 650/800 springs, GC bars set at medium position front soft position rear, -3.5 F camber 0.20 degree toe out -1.8 R camber 0.20 toe in. Not 100% sure on the toe measurements since it's been a while, but mild toe in/out between F/R.

The rebuilt diff made the biggest difference in my ability to put power down out of corners, and catch it when it does step out. It never snapped on me except when the RTABs were just sliding around in the RTAB hole and changing toe dynamically.

The car should NOT snap on you, so something is strange. Have you had another experienced BMW driver drive your car, and have they been able to replicate it?
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Last edited by Bimmerman325i; Mon, Sep-25-2017 at 06:54:57 PM.
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Discussing Suspension setup and sudden snap oversteer in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)