Rear sway bar disconnect

[E90ALLMANUAL]

Has anyone disconnected their rear sway bar for autocross duty? Did it reduce understeer or it was too loose?

[lowside67]

Disconnecting the rear swaybar will decrease rear roll stiffness which will likely have the exact opposite effect of what you are describing. Less rear roll stiffness most likely equals more understeer/less loose.

Mark

[spxxx]

Originally Posted by E90ALLMANUAL

Has anyone disconnected their rear sway bar for autocross duty? Did it reduce understeer or it was too loose?

No sway bar would generally cause more understeer

[alpho]

Disconnecting the rear sway bar makes no discernible difference from the stock bar. Connecting a bigger bar with no LSD will make it more twitchy, slower.

[E90ALLMANUAL]

Is this real life experience or are you guys assuming?

When I had my Miata, disconnecting the rear sway bar made the car rotate better. I know they are different cars but they are both RWD.

[YarkoDrives]

I'm going to run a few events with one rsb end link removed.

135i oem open diff.

I have a very loose alignment for autocross. 0 toe in rear. BMW Performance Springs and fsb.

the back end is manageable, but not quite predictable.

1. there's a limit where the backend comes out more suddenly than it's slip had indicated up to that point. (oem rear arms/bushes don't help but they should feel linear). the oem endlinks could be to blame.

2. sometimes I get snap oversteer (in the opposite direction from load). this is very much a symptom of having a rsb. (this may be aggravated by EDL/yaw sensor overload/safety)

Removing the RSB should help with both of these:

more roll in the back should solve 1. by giving a sooner but linear feel up to the limit of traction (or to the trailing-arm deflection:bind:snap).

should solve 2 by letting the inside wheel stay more on the ground, though it will have less weight on it.

[YarkoDrives]

last event with a RSB. snap oversteer, as I tried to correct out of the spin at end of video.

[fe1rx]

Originally Posted by YarkoDrives

last event with a RSB. snap oversteer, as I tried to correct out of the spin at end of video.

That was power oversteer, i.e. due to aggressive throttle input. It occurred right after an aggressive gear shift broke the rear traction.

Oversteer is not your problem, understeer is. You are driving at very high front slip angles and are overdriving your car. It only oversteers when provoked.

I have tried disconnecting the OE rear bar on a skid pad (logging lateral g, and steering angle to get understeer gradient). With fairly stiff springs on coil-overs I could not detect any difference with the bar disconnected. With softer springs, more of the total roll stiffness comes from the bars, so it might make a small difference in your case, but it would be moving your handling more towards understeer in that case, which won't help the root problem.

Beware when disconnecting one end link, the bar may rub on the drive shaft boot at certain roll angles and one-wheel bump conditions.

[The Wind Breezes]

One thing I notice is you're not yet used to steering the car with the throttle. Even a stock car will easily do what you demonstrate if driven improperly at the limit. A tip: excessive steering wheel input will actually increase understeer beyond the point where more wheel doesn't cause the car to turn in more.

[Kgolf31]

19mm bar. No issues

[katsooba]

Kgolf that a heck of an attack mode! you're on fire

[chris82]

take it off and see what you like better

[E90lova]

Originally Posted by E90ALLMANUAL

Has anyone disconnected their rear sway bar for autocross duty? Did it reduce understeer or it was too loose?

This is an E30 thing. I tried this on my 86 325e and it actually made the car very neutral but also comes with loose rear end as well. Felt like I had soft sidewall rear tires. What I did with that same car that is safer was 15x7" rear with 195s and 15x8 front with 205s with the rear sway intact. That wider stronger tire in front made the car neutral and faster in corners. :thsumbsup:

[z3papa]

I've run a car with no rear sway bar all the time, no sway for all but high transition courses, and a stock rear sway connected all the time. When I went without, I generally had between -3.5 to -4.0 front camber, and tuned in as much total grip up front, and then compensated my car's tendency to to snap oversteer by disconnecting the rear sway. That worked great for all but the most transition heavy courses (think West courses last several years) at which you could click off lost time as the year seemed to lag behind the front. When I had a half and and half setup, i.e. one where it would adapt to whatever type of course you had, it was a compromise as you were always shifting setup from non-transition to transition oriented setups and this was as I was implementing a custom Blanton diff. Finally, when I got it to the point where my diff was completely tuned along with suspension, the rear OE sway was reconnected but maximized grip in the rear to that of the front. Rule of thumb, don't dumb down one end to make up for excess grip on the good end of the car.

[Kgolf31]

Originally Posted by z3papa

I've run a car with no rear sway bar all the time, no sway for all but high transition courses, and a stock rear sway connected all the time. When I went without, I generally had between -3.5 to -4.0 front camber, and tuned in as much total grip up front, and then compensated my car's tendency to to snap oversteer by disconnecting the rear sway. That worked great for all but the most transition heavy courses (think West courses last several years) at which you could click off lost time as the year seemed to lag behind the front. When I had a half and and half setup, i.e. one where it would adapt to whatever type of course you had, it was a compromise as you were always shifting setup from non-transition to transition oriented setups and this was as I was implementing a custom Blanton diff. Finally, when I got it to the point where my diff was completely tuned along with suspension, the rear OE sway was reconnected but maximized grip in the rear to that of the front. Rule of thumb, don't dumb down one end to make up for excess grip on the good end of the car.

I still think the rear suspension on these are are x100 better than the past E36 and like suspension.

I think disconnecting an rear OE swaybar is not a good thing.

Proven example, IMO

[Ginger_Extract]

Wow, positive rear camber under load, guess that rear bar is doing something after all. A rear bar is still on my shopping list, to increase low speed rotation.

[z3papa]

Originally Posted by Kgolf31

I still think the rear suspension on these are are x100 better than the past E36 and like suspension.

I think disconnecting an rear OE swaybar is not a good thing.

Proven example, IMO

After all was said and done, my preference was to have the bar attached but wanted to explain the process of arriving at that conclusion.

[Taskmaster]

Originally Posted by Kgolf31

I still think the rear suspension on these are are x100 better than the past E36 and like suspension.

I think disconnecting an rear OE swaybar is not a good thing.

Proven example, IMO

I have a crush on your car