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      10-16-2023, 09:34 PM   #1
M3MATT
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unstable rear end under heavy braking (track use)

I noticed how under heavy braking the rear end seems to ďdanceĒ and become unstable on the track. Iím running KW V3ís and Iím thinking it may be me riding the bumpstops due to the softer spring rate.
Or I wonder if it could be my driving style

Iím also running Hawk dtc-70 all around with track fluids, lines, and rotors.


Did anyone else have this issue and/or fix it?
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      10-16-2023, 09:38 PM   #2
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what's your alignment like
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      10-16-2023, 10:51 PM   #3
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Quote:
Originally Posted by M3MATT View Post
I noticed how under heavy braking the rear end seems to ďdanceĒ and become unstable on the track. Iím running KW V3ís and Iím thinking it may be me riding the bumpstops due to the softer spring rate.
Or I wonder if it could be my driving style

Iím also running Hawk dtc-70 all around with track fluids, lines, and rotors.


Did anyone else have this issue and/or fix it?
I had exactly the same issue at the end of a straight with a hard braking zone and it ended up being the front upper control arms. If you're pushing it, the stock ones with rubber just flex too much and the rear end dances under very hard braking. I swapped in a set of the GAS monoballs:
https://germanautosolutions.com/gas-...ntrol-arms-v2/

It's been rock steady under the heaviest braking ever since. There's minimal added NVH and the steering feel is enhanced. Overall an excellent mod for a car that gets track time.
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      10-17-2023, 12:07 AM   #4
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Quote:
Originally Posted by pirategenes View Post
I had exactly the same issue at the end of a straight with a hard braking zone and it ended up being the front upper control arms. If you're pushing it, the stock ones with rubber just flex too much and the rear end dances under very hard braking. I swapped in a set of the GAS monoballs:
https://germanautosolutions.com/gas-...ntrol-arms-v2/

It's been rock steady under the heaviest braking ever since. There's minimal added NVH and the steering feel is enhanced. Overall an excellent mod for a car that gets track time.
I already gave GAS. Iím fully solid/spherical in every bushing. I got a bit carried awayÖ lol
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      10-17-2023, 12:26 PM   #5
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Quote:
Originally Posted by M3MATT View Post
I noticed how under heavy braking the rear end seems to “dance” and become unstable on the track. I’m running KW V3’s and I’m thinking it may be me riding the bumpstops due to the softer spring rate.
Or I wonder if it could be my driving style

I’m also running Hawk dtc-70 all around with track fluids, lines, and rotors.


Did anyone else have this issue and/or fix it?
Too much rear braking balance ,
go for a less aggressive brake pads at the rear.
rear wheels are locking up .

or too mucg rear toe in

Last edited by atopa2002; 10-17-2023 at 12:41 PM..
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      10-22-2023, 12:49 PM   #6
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I had same issue and thought it was the diff. Someone recommended playing with the coilovers, running the car full hard then full soft to see how behavior changes then dial it in. I found I was running the suspension too hard, softening the rear helped. Then I changed to supercar 3Rís which irradiated the issue (I was on old Nangang RS2)
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      10-22-2023, 01:07 PM   #7
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sometimes, it can be driver induced when gripping the steering wheel too hard and fighting the car.

a race couch, says to loosen up your grip on the steering wheel and don't fight it.
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      12-03-2023, 01:14 PM   #8
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I agree with @atopa2002 in that it's common for folks to go with DTC60 or a different version of a split pad setup. Maybe check out your brake disc temperatures when you come in, if the rear is a lot hotter than the front your instability is likely from brake balance.
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      12-03-2023, 03:57 PM   #9
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This is a classic issue heading into turn 2 at Laguna Seca. Solid rear subframe bushings and DTC off made it stop instantly. I used to run Hawk DTC-70ís too.

If that doesnít solve it then really focus on braking without turn in.

Good luck!
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      12-04-2023, 12:04 AM   #10
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Quote:
Originally Posted by Bimmer Barney View Post
This is a classic issue heading into turn 2 at Laguna Seca. Solid rear subframe bushings and DTC off made it stop instantly. I used to run Hawk DTC-70ís too.

If that doesnít solve it then really focus on braking without turn in.

Good luck!
DTC off? Like MDM off?
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      12-04-2023, 12:11 AM   #11
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Yes exactly. Turn off the nannies and the car wonít try to bring the rear tires back in line with the front, thus eliminated the booty shake.
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      12-04-2023, 05:37 AM   #12
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On my e46 m3 dedicated track car I once ran into rear brake instability/dancing after simultaneously lowering the rear ride height and increasing rear low-speed rebound damping. Reducing overall rebound (low and high speed) damping solved my problem.
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      12-04-2023, 09:05 AM   #13
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I get the same rear end steering, tail wagging issue under hard braking on the track, almost like the car wants to swap ends sometimes. At Road Atlanta this weekend coming into turn 10A around 140-150 mph and with very hard braking, the car was very unstable under braking and I don't think it was me incorrectly adding steering input.

Current mods are traction control OFF, Nitron R1 coilovers (700/1000lb springs), front monoballs, stock brakes with Hawk DTC-60 on all four corners, 18x10" 275/35/18 RE71RS tires.

Spoke with a few other E9x guys at several track days and all of them separately said, my car did this till I put a proper wing on the back.

I might try different brake pad compounds front to rear, but other than that I think I'll have to play with damper settings or adding a sweet rear wing and see what happens.

Edit: also could be a rear toe issue, I'm 0.2* toe in on each side, so that might be a little excessive
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Last edited by MineralWhiteF80; 12-04-2023 at 10:11 AM..
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      12-04-2023, 06:52 PM   #14
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Quote:
Originally Posted by Bimmer Barney View Post
This is a classic issue heading into turn 2 at Laguna Seca. Solid rear subframe bushings and DTC off made it stop instantly. I used to run Hawk DTC-70ís too.

If that doesnít solve it then really focus on braking without turn in.

Good luck!

Subframe bushingsÖ..someone gets it.

Another thought, does anyone realize the amount of time goes into a race teams even a semi-pro one with suspension setup? 3-ways have ups and downs. They provide great adjustability but much greater room for a less stable setup due to poor tuning.

Also, NEVER underestimate the power of the wrong spring rates.

Cheers,
E46e92
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      12-04-2023, 09:47 PM   #15
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Fwiw I have solid subframe bushings and my car still does that
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      12-04-2023, 11:08 PM   #16
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Quote:
Originally Posted by nycplumber View Post
Fwiw I have solid subframe bushings and my car still does that
Do you track with MDM/DTC off?
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      12-05-2023, 09:06 PM   #17
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Quote:
Originally Posted by Bimmer Barney View Post
Do you track with MDM/DTC off?
I pretty much drive exclusively with traction off. Rarely if ever use MDM
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      12-06-2023, 04:42 AM   #18
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I ran into this issue after lowering the rear ride height to solve a different handling issue and also increasing rear rebound damping. Raising the ride height a little and reducing rear rebound 1-click addressed the dancing.
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