Rear sway bar guidance

[aznbo187]

I'm still working on getting the 128 track ready, but next on the list is rear subframe bushings.

128 base didn't come with any rear bar at all and I haven't played with sway bars in general in dialing in the car so I'm pretty new here. I'd like to get a rear bar in there with the rear subframe install.

Is there a general starting point? I have yet to track the 1 so I'm not sure what the natural tendency is that the car wants to do. Should I start with a M3 bar and adjust from there, or go with something else?

Mainly will be doing road course, not much auto-x.

[tracer bullet]

I'll only suggest doing them in pairs / as a combo. Just one on its own may throw things off. The front is super easy to swap.

There are some pretty good threads of discussion here.

[wootloops]

It's largely going to depend on how stiff your springs are and what front bar you are running. Some track guys actually don't run a rear bar at all.

If you do add a bar I probably would start out with the m3 bars, and as tracer bullet said I would do it in pair with a front M3 bar (possibly a front E93 M3 bar since it's supposedly the stiffest of the stock bars). Then track the car a bit and see how it feels.

For comparison I am running stock base 128 front sway bar with 8k/16k F/R coilover spring rates and I think the car feels pretty good/neutral but I also am probably not driving the car at the limit enough. It seems like it might have just a tad of push mid corner but it's very little. A friend of mine has a e92 328 and he runs stock M3 sway bars front & rear but with M Performance suspension which is not very stiff (I think it's somewhat comparable to stock M3 spring rates)

[spidertri]

I came to the 128i from older BMWs and with the mindset of no rear sway bar works really well at getting the power down. However, I have progressively stiffened my car over the past two years and it has gotten better with each change.

I went from the stock sport bars to E92 M3 bars and they made the car feel immediately more responsive and supported when cornering. The rear bar is extremely effective on this chassis, especially with the springs sitting so far inboard. The ediff can handle it but just know that you will be getting it to activate more by going to bigger rear sway.

My latest setup this year is 500/800 springs with the E92 M3 bars and clutch type LSD. The most recent change being going from 700 to 800lb rear springs. At my local track (Carolina Motorsports Park) two weeks ago I went 2 seconds faster, just crushing my previous PB, I was blown away by how good the car feels on track.

The other crazy thing is they had the skidpad open and driving around at increasing constant speed the car still tends to understeer first. I didn't expect that with the increased rear spring rate and "big" rear bar.

[aznbo187]

Originally Posted by tracer bullet

I'll only suggest doing them in pairs / as a combo. Just one on its own may throw things off. The front is super easy to swap.

There are some pretty good threads of discussion here.

Noted.

Haven't been in a chassis where the subframe needs to be lowered to swap sway bars, so I was seeing if I could save myself a little work down the road.

It's largely going to depend on how stiff your springs are and what front bar you are running. Some track guys actually don't run a rear bar at all.

If you do add a bar I probably would start out with the m3 bars, and as tracer bullet said I would do it in pair with a front M3 bar (possibly a front E93 M3 bar since it's supposedly the stiffest of the stock bars). Then track the car a bit and see how it feels.

For comparison I am running stock base 128 front sway bar with 8k/16k F/R coilover spring rates and I think the car feels pretty good/neutral but I also am probably not driving the car at the limit enough. It seems like it might have just a tad of push mid corner but it's very little. A friend of mine has a e92 328 and he runs stock M3 sway bars front & rear but with M Performance suspension which is not very stiff (I think it's somewhat comparable to stock M3 spring rates)

I've yet decided on Coilovers but likely will be doing Ohlins or TCK. I have been eyeing the M3 bars but collecting a bit more feedback on what the general consensus is in terms of how the 128 behaves.

I came to the 128i from older BMWs and with the mindset of no rear sway bar works really well at getting the power down. However, I have progressively stiffened my car over the past two years and it has gotten better with each change.

I went from the stock sport bars to E92 M3 bars and they made the car feel immediately more responsive and supported when cornering. The rear bar is extremely effective on this chassis, especially with the springs sitting so far inboard. The ediff can handle it but just know that you will be getting it to activate more by going to bigger rear sway.

My latest setup this year is 500/800 springs with the E92 M3 bars and clutch type LSD. The most recent change being going from 700 to 800lb rear springs. At my local track (Carolina Motorsports Park) two weeks ago I went 2 seconds faster, just crushing my previous PB, I was blown away by how good the car feels on track.

The other crazy thing is they had the skidpad open and driving around at increasing constant speed the car still tends to understeer first. I didn't expect that with the increased rear spring rate and "big" rear bar.

M3 bar seems the most organic upgrade. I think I will start with that and adjust after some track time.

Skidpad, my experience with lower power cars is they often don't have the torque to kick the rear out without pushing. Try to momentarily let go of the throttle to shift the weight of the rear and sharply back on. Countersteer and steer with throttle. Should be fun times with the LSD and open skidpad!

[spidertri]

Oh, no, don't worry, I had no problem making it slide, just relaying the steady state behavior.

[Gary@simod.net]

We have a 135i race car and have a few customers with 1 series track cars.

If you do sway bars look at Hotchkis bars they are far better than any OEM bars. With a lot of aero they tend to like less front bar, which is anti what you do in E36/46 cars.

Use aluminum rear subframe mounts. Zero NVH on the Street. The easiest to install are the Rev Shift aluminum rear subframe mounts you can put them in with a deadblow hammer. The FULL solid aluminum mounts are a pain to put in due to the design of the subframe on the E8X/9X.

I have a suspension company we have V2 of our remote damper for the E8x/9x out along with single adjustable. Our valving in both, lifetime warranty on dampers. We have our triple adjustable on the 135 race car and double remotes on our TTRS.

https://contactsuspensionengineering.com