Rear sway bar question

[m3f_Baby ///M3]

Lately, I've been reading a lot about whether a thicker rear sway bar is needed for the performance enhancement of the E36 M3. The consensus seems to show the following:



1. Consider all other adjustments and suspension fine tuning before actually installing aftermarket sway bars.



2. A bigger front sway bar corrects the understeering nature of the E36. This effective is counter intuitive and opposite of the what a larger front sway bar does to other cars.



3. The rear sway bar can be deleted, provided that the rear springs are stiff enough to reduce the body roll.



4. Installing a bigger rear sway bar requires reinforcing the sway bar mounting tabs.



As of now, my car has the following suspension components:



Vorshlag camber plates

AST4100 coilovers

Hyperco 450lb front and 550lb rear springs

225/40/18 and 255/35/18 tires (36psi all around)

Eibach 26mm front sway bar

Stock rear sway bar



The 450/550lb spring combination is really the harshest setting I would like for now. As it is, the car has a very neutral handling characteristic, maybe a very slight understeer when it's pushed hard. Body roll is not terrible.



The question is, should I go with a bigger rear sway bar to help the car handle better for street driving (and occasional canyon runs)?



Eibach makes two types of rear sway bar for the E36. The 24mm for the M3 and the 21mm for the standard E36. Which of these is a better choice?



Will I compromise the performance of my suspension setup with a larger rear bar?



I would hate to have a tail happy E36 but wouldn't mind having a sharper turning rear end in case I take the car to an autocross event.



Any opinions?



Thanks in advance.



Jon

[m3f_fiveightandten]

Putting a stiffer bar in the rear will make the rear more apt to give up traction.


What are your alignment specs (front and rear camber, most importantly)? If the car is already pretty neutral, putting a rear bar on could make it a bit tail happy in some situations. I have the Eibach M3 sway bar kit. I was running the rear for a while, but I put the stock bar back on. It's pretty balanced like that, but my spring rates are a lower than yours, so things are different. High spring rates mean that the bar works less (less travel for it to deflect).


Personally, based on your descriptions and your setup, I don't think you need it. But everyone has different preferences, and I haven't driven your car. You have nothing to loose but money if you decide to experiment with it. But I would recommend welding reinforcement tabs on, as you mentioned above. I have the AKG set and they work fine.

I would hate to have a tail happy E36 but wouldn't mind having a sharper turning rear end in case I take the car to an autocross event.

The front end steers the car. Changes to the rear end don't yield sharper turning, they change the handling balance of the car (and how much it rolls or how easily it puts power down). I've found that I get plenty of throttle induced oversteer at autoX without the rear bar. But the car is definitely easier to rotate with it there. It's a tradeoff. Without it, I can put power down earlier and easier. With it, I can rotate the car easier. It depends on what you want out of it.


ALL of that is only based on your relatively high spring rates, and presumed low ride heights. A stock car should definitely have both bars.


EDIT: I just realized you're running 225's and 255's. Get a squared setup on the car if you want the handling to be a touch more neutral without oversteer issues. Or, run 245's in the rear at least. 225 to 255 is a big differential for a staggered setup.

[m3f_Baby ///M3]

Thank you very much for the helpful comments and feedback!



Although I should, I don't have my alignment specs with me at the moment. Interestingly, the outer edges of my rear tires are wearing out much quicker than the rest? This is weird because I can visualize a slight negative camber on the rear tires.



Since you have lower spring rates and found no need for the rear sway bar, am I correct to assume that it's even less likely that I'll be needing one? If I stick with my stock rear sway, is it beneficial to weld on the reinforcement tabs?



Thanks for pointing out that upgrading the rear sway does not mean sharper turning. I guess at this point, whether to upgrade the rear sway bar only is a matter of how easy I want to put the power down in the back end. Is there any advantages/disadvantages to either option for spirited street driving? I am making around 380rwhp.



Another question I have is that typically aftermarket companies sell both front/rear sway bars for the E36 M3 as a set. Is this purely done from a marketing standpoint?



I am sorry for the typo. My fronts are 235s, not 225s.



Jon

Putting a stiffer bar in the rear will make the rear more apt to give up traction.



What are your alignment specs (front and rear camber, most importantly)? If the car is already pretty neutral, putting a rear bar on could make it a bit tail happy in some situations. I have the Eibach M3 sway bar kit. I was running the rear for a while, but I put the stock bar back on. It's pretty balanced like that, but my spring rates are a lower than yours, so things are different. High spring rates mean that the bar works less (less travel for it to deflect).



Personally, based on your descriptions and your setup, I don't think you need it. But everyone has different preferences, and I haven't driven your car. You have nothing to loose but money if you decide to experiment with it. But I would recommend welding reinforcement tabs on, as you mentioned above. I have the AKG set and they work fine.



The front end steers the car. Changes to the rear end don't yield sharper turning, they change the handling balance of the car (and how much it rolls or how easily it puts power down). I've found that I get plenty of throttle induced oversteer at autoX without the rear bar. But the car is definitely easier to rotate with it there. It's a tradeoff. Without it, I can put power down earlier and easier. With it, I can rotate the car easier. It depends on what you want out of it.



ALL of that is only based on your relatively high spring rates, and presumed low ride heights. A stock car should definitely have both bars.



EDIT: I just realized you're running 225's and 255's. Get a squared setup on the car if you want the handling to be a touch more neutral without oversteer issues. Or, run 245's in the rear at least. 225 to 255 is a big differential for a staggered setup.

[m3f_NolliM3]

Yes, I agree that Nick gave good feedback. I have BMW 26mm (from 318) front sway to install with 450lbs spring rate coilovers front and rear on square setup. I wish I could share.

[m3f_Bimmerman325i]

I wouldn't mess with the bar if you're happy with the balance of the car. I drove for years on stiff-ish coilovers, track alignment, and 325iS front bar/stock rear bar. I went to GC front/rear bars, and....the car is stiffer and I can tune the car more, which was my goal. I'm not convinced it did much though, the car handled really well before and was nice and compliant. Now it's a bit less compliant, but my friends no longer make fun of the body roll, so...hooray?


If you want to try removing the rear bar, just undo one of the rear endlinks from the control arm. My suspicion is your spring rates aren't high enough to really make that setup work.


Honestly unless you want the ability to more easily tune the front/rear balance of the car...I wouldn't mess with sways.

[m3f_vmbray]

Agree with what's been said, and I've installed a HR rear sway but haven't autocrossed it yet. I think rear sway delete is for higher spring rates as well.


Everything suspension related is a compromise and is dependant on the whole setup. For example, you should choose sway thickness based on what tires and how much grip they have, and thus how much body roll is created. Hoosiers should need bigger bars than a 200 tread wear tire for example.


I am lifting a wheel a lot when racing so I am trying the rear bar. On the street I already like it, feels more balanced and puts down power better out of a corner (while still turning but haven't pushed it 100% yet), due to less squat, or at least it feels that way. Remember even with rear springs 100 lb harder, the inboard location renders a lower rate than the fronts. I've thought about running 400/550 just to try.


You also might reduce rear camber a touch to counteract the straight line grip loss but that might not be good at speed in a slalom. I'm a little nervous about higher speeds in slalom because the car is so good now, but it lifts all the time so it's worth trying. Also I think it will help with lower speed understeer because yes a bigger front sway helps BUT you are still causing the weight to transfer quicker in the front so it's not a magic bullet, and the rear sway will transfer weight quicker in the rear and should help balance it at lower speeds.


Haven't had time to go run it because we're moving soon.


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