sway bar questions.

[e30leigh]

hi there guys.

im asking the guys in the know. about sway bar effects on handling.

its my understanding that when fitting a larger sway bar in the back of a rwd, such as an e30, it will promote oversteer if the front has not been replaced with a larger one to compensate.

is this true? my last car was fwd and it was the opposite with that. it would understeer if i had a large one in the front only.

ive been given a 19mm rear sway bar for my e30. and my fears are that it will promote oversteer. and the lil old 318i has just enough power to get me into trouble and not enough to get me out of it.

basically i need to know if its ok to fit the bar or if i should wait till i get a larger front one too.

thanks, leigh

[Van Westervelt]

Wait. A lot of people will recommend not even using a rear bar at all on e30s. I usually upgrade the front bar with all reinforcements/mounts, and leave the rear bar stock, but redo the mounts etc.

[fporro]

^ yeap, specially track guys.

I'm running a 25mm front and 22mm rear, very happy with them on my 325iC .

[oldmann]

My DD is same car, I found a 19mm rear bar from 325ix, and 22mm front bar from 325i vert, both on car now, very pleased with the result. billstein hds all around with stock springs.

[110stx]

I run a 25mm front bar and stock rear bar on my autoX car.

I would not install the rear bar by itself.

[TobyB]

Yes, to your original question, stiffening the rear roll rate will trend you towards oversteer,
everything else being equal. You will get more weight transfer at that end in corners, and
thus reduced rear lateral grip, relative to the front.
Likewise, a smaller front bar would do the same- the front suspension would
become more roll compliant, the 'roll loading' would be transferred to the rear more,
and you'd again head toward oversteer.
Conversely, a bigger front or a smaller rear will head towards understeer.

Now, it's important to realize that a roll bar is pretty soft compared to your springs. So
if you're running 600# springs all around, a mm or 3 in the roll bar isn't going to make very much
difference at all in the overall car balance.

And that said, a 19mm bar is not a particularly
stout thing, so if you're understeering now, it's not going to make the car immediately
undrivable- it'll just understeer less.
Once you get used to the difference, it'll just be different. Then you can see if you
like it- or not.

fwiw.

t

[Jaxx_]

Depends on what you want. Track guys don't recommend using a rear sway because you can get on the throttle earlier. You'd have to trail brake and use the throttle to steer the car. If you want a neutral setup at a constant velocity, a front only sway setup probably isn't going to work well.

[e30leigh]

i have 440 front and 675 rear spring rates. and bilstien sports. i want a rather well balanced set up. with the stock sway bars its pretty well balanced. but in high speed corners theres just alittle too much roll for my liking.

my thoughts were the 19mm sway bar in the back, its not huge. but enough to take some roll out, i may even change it to factory if it gets too tail happy. and a larger 25mm in the front. ill also be raising the rear subframe for roll centre improvement. and all new stiffer bushes in the back and m3 cab in the front. with full braces ect.

my only issue is i like to go out drifting on the odd day. so i guess i could swap bars in the back if need be.

[dothadance]

My DD is same car, I found a 19mm rear bar from 325ix, and 22mm front bar from 325i vert, both on car now, very pleased with the result. billstein hds all around with stock springs.

just a heads up. neither of those numbers are correct

[Smelser]

I have to check how BMW mounts say bars, but if its like GM, You can adj the side to side by shortening where and how it is mounted to the control arm. its mounted to the car body, then shorten or lengthen the adj point on the controlarm will also have an effect.

You can just take them both off all together. we do on dirt, and it allows the car to lean hard and get good bite on the right side when sliding in the dirt!!!

[e30leigh]

can car will be on the road/ track only. its way too low for dirt haha. ill get a matching pair i think. from who ever i end up getting them from.

[yeaseth]

It depens on your springs rates as well. When I did 22mm sways front and 19 rear with my eibach springs the car handled awesome, just enough oversteer to pivot the car around. Now I have those same sway bars with 450 and 750 spring rates and my back end pops out even easier which is exactly how I like the car to handle for autocross but im interested to see what my car will do with the stock rear sway bar :)