Sway Bar Sizes

[Earendil]

Stock:

318i(m10): Front: 18mm Rear: none
318is(m42): Front: 20mm Rear: 12mm
318ic(m42): Front: 21mm Rear: 12mm
325e(pre 9/86): Front: 18.5mm Rear: 12mm
325e(9/86): Front: 20mm Rear: 12mm
325i(m20): Front: 20mm Rear: 12mm
325is(m20): Front: 20mm Rear: 12mm
325ic(m20): Front: 21mm Rear: 12mm
325ix(M20): Front: 17mm Rear: 14.5mm
325ix Touring(M20): Front: 18mm Rear: 14.5mm
M3(s14): Front: 19mm Rear: 14.5mm



Aftermarket:

AC Schnitzer: Front: 20mm Rear: 16mm
Eibach: Front: 20mm Rear: 16mm
Suspension Techniques: Front: 22mm Rear: 19mm
Ireland Engineering (adjustable): Front: 25mm Rear: 22mm
H&R (adjustable): Front: 22mm Rear: 18mm
Racing Dynamics Early Style (adjustable): Front: 22mm Rear: 16mm
Racing Dynamics Late Style (adjustable): Front: 22mm Rear: 19mm
M-Technik: Front: 20mm Rear: 14.5mm

If you have more info to add, post here and i will update the faq.

Enjoy.

I'm curious what the point of all the 20mm aftermarket bars are? Are they made out of a different and thus stiffer material? And if so, why measure them in mm instead of some sort of force per distance rating?

Unless of course the multitude of 20mm bars are all for the 318?

[nando]

because stiffness is directly related to the diameter of the bar. bigger bar = stiffer. generally they're all made of the same sort of spring steel.

you can figure out the relative stiffness if you only know the diameter. (new/old)^4 - so a 20mm swaybar is almost *8* times stiffer than a 12mm bar. you can see how many consider such a large rear bar to be massively oversized.. that would be like increasing your front spring rates from stock to ~1300/1800#.

[Earendil]

because stiffness is directly related to the diameter of the bar. bigger bar = stiffer. generally they're all made of the same sort of spring steel.

you can figure out the relative stiffness if you only know the diameter. (new/old)^4 - so a 20mm swaybar is almost *8* times stiffer than a 12mm bar. you can see how many consider such a large rear bar to be massively oversized.. that would be like increasing your front spring rates from stock to ~1300/1800#.

So if they are all the same material, why the same size front aftermarket bars?

AC Schnitzer: Front: 20mm Rear: 16mm
Eibach: Front: 20mm Rear: 16mm
M-Technik: Front: 20mm Rear: 14.5mm

That little math bit, if correct (:)) is quite a useful piece of info that I hadn't seen mentioned in a swaybar discussion before. Make me think a 22mm upgrade from 20 might actually be worth something (46% increase).

[blefevre]

Because they run a business. They want to compete in the market of sway bars. You can take your pick on where you send your money.

[nando]

So if they are all the same material, why the same size front aftermarket bars?

AC Schnitzer: Front: 20mm Rear: 16mm
Eibach: Front: 20mm Rear: 16mm
M-Technik: Front: 20mm Rear: 14.5mm

That little math bit, if correct (:)) is quite a useful piece of info that I hadn't seen mentioned in a swaybar discussion before. Make me think a 22mm upgrade from 20 might actually be worth something (46% increase).

stiffer isn't neccesarily better. especially the massive increases people like to go about.

[Earendil]

stiffer isn't neccesarily better. especially the massive increases people like to go about.

I agree. But unless you had a 318, why would you buy a 20mm sway bar unless someone stole yours off your car? (Excluding the ix since it requires a different front sway entirely).

I guess I'm just puzzled why an aftermarket performance parts company would sell a part that is identical to the stock part. A stock part that doesn't really wear out. It seems they would attempt to sells something smaller or larger, anything but what most E30's have.

If a 20mm bar doesn't perform the same as every other 20mm bar, that would explain things, but you seem to be saying that isn't the case?

So if a stock E30 buys, say, the Eibach kit (20mm and 16mm) they will end up with a different rear bar, but they might as well be installing a freshly painted stock bar in the front?

I still feel like I'm missing something here. I can't believe that these companies are either that stupid/conniving, or that the buyers are that stupid/ignorant. Maybe when it comes to things I can't believe, I'm the one that's that stupid/ignorant :)

[blefevre]

I get what you are saying. I have never seen an ACS or Eibach bar. It is possible they are adjustable with different mounting locations for the sway bar link.

[ieatpeople]

i have a new, never installed st rear bar (19mm) for sale, $40+ shipping. pm me if interested.

[jdog]

Sent you a PM on the rear bar.

[pantelones]

basically if you dont understand what makes a suspension feel stiff then you will probably buy aftermarket sway bars, ignorance is bliss i guess. bigger diameter bars are only necessary when you run really soft springs and you need the extra force of a bigger bar, it helps keep the wheels on the ground and reduce the added body roll from soft springs. if you run stiff springs (which most people who would buy aftermarket sway bars would be) you dont need bigger bars, the vert 21mm front and 14.5mm XI rear would be a perfect set up for a little stiffer suspension, and cost less than $100. i think its pretty silly to spend $300+ on new swaybars.

[NufnSus]

bump for a nice info resource

btw, can anyone confirm that the E30 320i came with an 18.5mm Front Bar?
...at least that's what my callipers say I've got, and it sure looks OEM (& in need of a new p/coat)

also, this;
How Sway Bars work
pretty sure I've seen it linked elsewhere within the cosmos of this forum before, but I figured this is maybe a more appropriate place.

[Earendil]

basically if you dont understand what makes a suspension feel stiff then you will probably buy aftermarket sway bars, ignorance is bliss i guess. bigger diameter bars are only necessary when you run really soft springs and you need the extra force of a bigger bar, it helps keep the wheels on the ground and reduce the added body roll from soft springs. if you run stiff springs (which most people who would buy aftermarket sway bars would be) you dont need bigger bars, the vert 21mm front and 14.5mm XI rear would be a perfect set up for a little stiffer suspension, and cost less than $100. i think its pretty silly to spend $300+ on new swaybars.

As with most things, this "depends", right? I know the Pro-3 guys run hella stiff suspension with a larger front sway bar. That said, they run a stock rear bar (or in some cases no rear bar?). But back to the "depends", they also are trimming for race application, and have crazy [compared to street] camber, and sticky tires.

In general, I think you're right. But it's not an absolute if my understanding is correct.

[pantelones]

As with most things, this "depends", right? I know the Pro-3 guys run hella stiff suspension with a larger front sway bar. That said, they run a stock rear bar (or in some cases no rear bar?). But back to the "depends", they also are trimming for race application, and have crazy [compared to street] camber, and sticky tires.

In general, I think you're right. But it's not an absolute if my understanding is correct.

Oh of course that statement is not an absolute. What size bars and how you have them adjusted all comes down to the specific application, and driver preference. Though general in a street application you really don't need that big of sway bars, but in an actual race car it becomes a whole other story. Sway bars do play a role in your over-steer/under-steer, and they can be used as a tool to correct one or the other to an extent.

[carguy101]

I saw this and thought it would be useful here http://www.houseofthud.com/cartech/swaybars.htm

[Earendil]

I saw this and thought it would be useful here http://www.houseofthud.com/cartech/swaybars.htm

I saw this too... Three posts above this. But thanks :)