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      07-20-2018, 07:45 PM   #1
CO_Steve
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Rear sway bar upgrade only

I have a '15 M235 manual rwd with Dinan springs. I'm about to install the lsd and my shop says changing the rear sway bar would only add a bit more labor. Not a track car, just street and a couple of AX every season. Not serious. The car always felt to me like the rear bar was way too small. Has anyone run just an upgraded rear. Trying to maintain good street manners but don't want to severely unbalance the car.

Last edited by CO_Steve; 07-21-2018 at 05:06 PM.
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      07-21-2018, 02:31 PM   #2
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Not upgraded my 2 series, but I fitted the 235/40 rear ARB on my F30. Maybe a great improvement going from 13mm to 15mm. I expect the 2 series would benefit the same, just to give a little more rear stiffness.

I wouldn't go very stiff though.
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      07-21-2018, 05:05 PM   #3
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Quote:
Originally Posted by NISFAN View Post
Not upgraded my 2 series, but I fitted the 235/40 rear ARB on my F30. Maybe a great improvement going from 13mm to 15mm. I expect the 2 series would benefit the same, just to give a little more rear stiffness.

I wouldn't go very stiff though.
That was my intention but there are only a few choices. Both the Dinan and Hotchkis say they are 100% stiffer than stock in the rear. Not calibrated on if that's too much. For your 13 to 15 change for a solid bar that would be 50% stiffer (approx).
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      07-21-2018, 05:40 PM   #4
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Quote:
Originally Posted by CO_Steve View Post
Both the Dinan and Hotchkis say they are 100% stiffer than stock in the rear. Not calibrated on if that's too much.
You might try calling Bimmerworld to ask them about the Hotchkis unit (that they sell) - you'll get a straight answer from them as to the difference it would likely make given your needs and how you use your car.
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      08-13-2018, 03:44 AM   #5
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If upgrading the rear springs is an option, try going up in rate first.

A larger rear bar will take away the effectiveness of the LSD if you are still in a turn, especially so if you are running a gear type LSD.
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      10-28-2018, 08:05 PM   #6
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Quote:
Originally Posted by HP Autosport View Post
If upgrading the rear springs is an option, try going up in rate first.

A larger rear bar will take away the effectiveness of the LSD if you are still in a turn, especially so if you are running a gear type LSD.
Please help me understand a bit better. The rear bar on the M235i is Somewhere around 12mm to 14 mm I believe with the eDif
The M2 if I'm not mistaken is around 25mm with a true LSD.
so how is upgrading the rear Stabilizer bar going to decrease the effectiveness of the LSD in a M235???
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      10-28-2018, 09:51 PM   #7
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Quote:
Originally Posted by Shadowfax028 View Post
Please help me understand a bit better. The rear bar on the M235i is Somewhere around 12mm to 14 mm I believe with the eDif
The M2 if I'm not mistaken is around 25mm with a true LSD.
so how is upgrading the rear Stabilizer bar going to decrease the effectiveness of the LSD in a M235???
The larger rear sway will have more roll stiffness and will constantly try to lift the inside rear tire off of the ground in a turn. If you are looking for more roll stiffness, it's best to use springs or add a larger front bar first.
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      10-29-2018, 06:28 PM   #8
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Would definitely suggest it if doing the LSD at the same time, that and Diff Bushings, 100%

It will make the car sharper on turn-in and corner exits, and a bit more playful at the same time. If not doing the LSD, you'll create a lot more inner-wheel spin on corner exits..
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      11-19-2018, 03:05 AM   #9
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Quote:
Originally Posted by HP Autosport View Post
The larger rear sway will have more roll stiffness and will constantly try to lift the inside rear tire off of the ground in a turn. If you are looking for more roll stiffness, it's best to use springs or add a larger front bar first.
I have a 32mm sway bar in the front now!
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      11-19-2018, 03:09 AM   #10
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Quote:
Originally Posted by Dylan86 View Post
Would definitely suggest it if doing the LSD at the same time, that and Diff Bushings, 100%

It will make the car sharper on turn-in and corner exits, and a bit more playful at the same time. If not doing the LSD, you'll create a lot more inner-wheel spin on corner exits..
I have a Mperformance LSD now , planning to upgrade the subframe and Diff bushing. Would also like to upgrade the RSB while I'm at it.
The largest RSB I can find is a 20mm non adjustable
Do you know of anything larger that will work?
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      11-23-2018, 06:32 PM   #11
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Quote:
Originally Posted by Shadowfax028 View Post
I have a 32mm sway bar in the front now!
Add more rear springs.
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      11-23-2018, 07:04 PM   #12
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Quote:
Originally Posted by CO_Steve View Post
Not a track car, just street and a couple of AX every season. Not serious. The car always felt to me like the rear bar was way too small. Trying to maintain good street manners but don't want to severely unbalance the car.
Quote:
Originally Posted by HP Autosport View Post
The larger rear sway will have more roll stiffness and will constantly try to lift the inside rear tire off of the ground in a turn. If you are looking for more roll stiffness, it's best to use springs or add a larger front bar first.
Quote:
Originally Posted by Shadowfax028 View Post
Would also like to upgrade the RSB while I'm at it.
The largest RSB I can find is a 20mm non adjustable
Just curious: why do you want a larger bar - how do you expect that it will improve your car?

When I had my build done, I made it clear that getting this tank to turn in was a principal objective of mine. My signature shows what I've done, and I was informed by the builder that if I wanted better turn-in a front sway bar was the next step - but at the price of some street comfort. I did ask about a rear bar. I don't remember the response - basically, it wasn't part of the conversation. FWIW, my focus is Mid-Ohio, a handling track.
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Last edited by dradernh; 11-23-2018 at 07:11 PM.
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      11-24-2018, 09:24 AM   #13
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Quote:
Originally Posted by dradernh View Post
Just curious: why do you want a larger bar - how do you expect that it will improve your car?

When I had my build done, I made it clear that getting this tank to turn in was a principal objective of mine. My signature shows what I've done, and I was informed by the builder that if I wanted better turn-in a front sway bar was the next step - but at the price of some street comfort. I did ask about a rear bar. I don't remember the response - basically, it wasn't part of the conversation. FWIW, my focus is Mid-Ohio, a handling track.
The current RSB on the M235i if I'm not mistaken is 12mm. 15mm on the convertible. For a Autocross car that is called on to manage weight transfer from left to right at 40+ MPH it just isn't enough. The M235i for the most part comes from the factory with a open Differential. So a 12 to 15 mm RSB is probably enough for a DD aka grocery getter.

Hell, I had a Miata that came with a 12mm RSB. I have put a MPERFORMANCE LSD in this car and coded out the eDif nannies. So after driving in several events and driving the M2 with a 24mm RSB its obvious this car NEEDS a larger RSB. Heck BMW recognizes this thus the 24mm RSB on the M2.

The challenge for us M235i owners is finding a larger then 20mm RSB that is adjustable. What would be really be kool is for Bryan at Karcepts to build one of his most impressive three piece adjustable Sway Bars that he fabricates for the S2k and Miata crowd for us M235i owners with a true LSD.

Last edited by Shadowfax028; 11-24-2018 at 04:05 PM.
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      11-24-2018, 09:20 PM   #14
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Quote:
Originally Posted by Shadowfax028 View Post
The current RSB on the M235i if I'm not mistaken is 12mm. 15mm on the convertible. For a Autocross car that is called on to manage weight transfer from left to right at 40+ MPH it just isn't enough. The M235i for the most part comes from the factory with a open Differential. So a 12 to 15 mm RSB is probably enough for a DD aka grocery getter.

Hell, I had a Miata that came with a 12mm RSB. I have put a MPERFORMANCE LSD in this car and coded out the eDif nannies. So after driving in several events and driving the M2 with a 24mm RSB its obvious this car NEEDS a larger RSB. Heck BMW recognizes this thus the 24mm RSB on the M2.

The challenge for us M235i owners is finding a larger then 20mm RSB that is adjustable. What would be really be kool is for Bryan at Karcepts to build one of his most impressive three piece adjustable Sway Bars that he fabricates for the S2k and Miata crowd for us M235i owners with a true LSD.
The "adjustable" part of your dilemma could perhaps be addressed with adjustable endlinks. That is, get as think a sway bar as you need and use adjustable endlinks to tune it the way you want. Just a thought.

PS: the difference in handling between the M2 and M235i, though, hardly boils down to thicker sway bars alone. there's way too many differences between the two, e.g., subframe bolted to the frame directly as opposed to via bushings, different springs and shocks, harder bushings throughout, etc.
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      11-26-2018, 02:43 AM   #15
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Quote:
Originally Posted by Shadowfax028 View Post
I have a Mperformance LSD now , planning to upgrade the subframe and Diff bushing. Would also like to upgrade the RSB while I'm at it.
The largest RSB I can find is a 20mm non adjustable
Do you know of anything larger that will work?
I couldn't find anything adjustable for the rear, so settled for the Hotchkis set (front 3 settings). No complaints, the car handles great, and is plenty stiff on the lowest setting, especially with higher spring rates and uprated bushings..
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      12-05-2018, 10:52 AM   #16
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Quote:
Originally Posted by Dylan86 View Post
Would definitely suggest it if doing the LSD at the same time, that and Diff Bushings, 100%

It will make the car sharper on turn-in and corner exits, and a bit more playful at the same time. If not doing the LSD, you'll create a lot more inner-wheel spin on corner exits..
Just had the Turner solid Aluminum subframe bushings and H & R 20mm RSB installed. The M235i has responded extremely well to both upgrades.
Honestly cant tell the solid bushings are in.

The RSB definitely helps this car.
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      12-06-2018, 10:58 AM   #17
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Quote:
Originally Posted by Dylan86 View Post
I couldn't find anything adjustable for the rear, so settled for the Hotchkis set (front 3 settings). No complaints, the car handles great, and is plenty stiff on the lowest setting, especially with higher spring rates and uprated bushings..

After installing the LSD, rear subframe bushings and RSB.
What alignment specs did you settle on for autocrossing?

Camber, caster, toe in toe out?
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      12-07-2018, 03:09 PM   #18
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Quote:
Originally Posted by HP Autosport View Post
If upgrading the rear springs is an option, try going up in rate first.

A larger rear bar will take away the effectiveness of the LSD if you are still in a turn, especially so if you are running a gear type LSD.
Do you have a set of rear springs that are higher in rate?
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      12-07-2018, 04:01 PM   #19
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Quote:
Originally Posted by Shadowfax028 View Post
Do you have a set of rear springs that are higher in rate?
For coilovers will be easy. If you are running sport springs, a higher rate spring could potentially change the ride height as well.

PM us what you have on the car and we will respond.
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