135i Sway Bar diameters

[J-Sud]

Any word on the Stock sway bar sizes?

Eibach has a set 28mm front and 15 mm rear
H&R is 27mm front and 20mm rear.

I am wondering which would be a better balance in comparison to the stock size.

[MVF4Rrider]

I'm sure either is a big improvement over OEM. Size doesn't equal strength necessarily so it's near impossible to compare just on size differences alone. Design and materials (actual strength), and whether solid or hollow, matters as well. I prefer the H&R because the bushings stay quiet for life and the company is highly reputable for making a superior product.

[mikeo]

FYI, the OE front bar is hollow on the 135i, not solid like all the aftermarket bars (so far). That makes a diameter comparison to stock very complicated, not to mention aftermarket front bars will add poundage.

[blacknbean]

hotchkis makes hollow sway bars as well that are lightweight. ill be looking into them when i get my 135. hotchkis makes good stuff http://www.e90post.com/forums/showthread.php?t=123680

[mikeo]

I wonder when Hotchkis will have a 135i hollow bar package available?

[BMW Dreamer]

I wonder if strong large rear sway bars will change the balance? Making it handle worse? Don't you have to get the correct front and rear upgraded at the same time, and tested for real additional handling. You don't just throw on a thick rear bar and think it will handle better. So tell me whats up?

[Orb]

Originally Posted by mikeo

FYI, the OE front bar is hollow on the 135i, not solid like all the aftermarket bars (so far). That makes a diameter comparison to stock very complicated, not to mention aftermarket front bars will add poundage.

The stock bars are solid so I can’t imagine were you got this from. The calculations are fairly easy for stiffness by canceling the terms given all thing being equal:

D= Outside Diameter
d= Inside diameter

Solid Bar Stiffness = D^4
Hollow Bar Stiffness= D^4 – d^4

The modulus for steel are almost all the same so material doesn’t make a difference. The weight difference is not much BTW.

Orb

[mikeo]

Orb, it's in BMW specs and on a 1Addicts sticky, but I'm not going to do a search right now. OE front bar is hollow, believe it.

Edit: 3/24/08.
E82 Coupe Internal Training Manual, page 19.
"The springs and dampers have been specifically adapted to the E82 in terms of engine and car weight. They differ, therefore, from those in the E90. In the interests of weight, the front axle of the E82 is fitted with a tube-type anti-roll bar. Sports suspension tuning is available as an option..."

[CTB]

Originally Posted by Jeff1962

I wonder if strong large rear sway bars will change the balance? Making it handle worse? Don't you have to get the correct front and rear upgraded at the same time, and tested for real additional handling. You don't just throw on a thick rear bar and think it will handle better. So tell me whats up?

If you have experience with tuning suspensions and you want less understeer, then yes, you do throw on a thicker rear bar and think it will handle better. However, it pays to do a little work ahead of time to determine just how far you want to go. Put too much rear bar on and now you have an oversteer nightmare. Sounds fun, but it isn't. Everyone has their own taste for handling and what works for them. If there is a rear bar that offers a small size increase over stock, then perhaps that will work for some folks who just want a more neutral car. Others may want to increase the front roll stiffness as well to decrease the whole car's roll amout, and so on. And as noted above, the spring rate of a sta-bar is proportional to the diameter to the fourth power; thus, small changes in bar diameter result in big changes in roll stiffness. You also just can't look at the bar diameters alone. You have to look at bar efficiency/motion ratio. A sta-bar that attaches directly to a strut or knuckle will be a lot more effective than one that attaches in the middle of a control arm; with the efficient design, you'll see big changes with small changes in bar diam. With inefficient designs, you need to make bigger bar diam changes to get the same end result. Since I haven't been able to see a 1 suspension yet, I don't know how the bars work, but it is something that needs to be considered.

[BMWeber]

Originally Posted by Orb

The stock bars are solid so I can’t imagine were you got this from. The calculations are fairly easy for stiffness by canceling the terms given all thing being equal:

D= Outside Diameter
d= Inside diameter

Solid Bar Stiffness = D^4
Hollow Bar Stiffness= D^4 – d^4

The modulus for steel are almost all the same so material doesn’t make a difference. The weight difference is not much BTW.

Orb

Material and condition of that material (heat treating and such) can make a large difference.

[white911]

I know how sway bars work on the 911 and using them, I can adjust them from fast and furious drift car to a plowing pig (sort of like a Caprice or a Crown Vic). Also, the sway bars on the 911 are both hollow and thinner then the stock bars.

The sway bars on the 135I follow a more tortuous path then what I am used to. What effect do all the bends in the lever arms have on the effective length of the arms? Are any manufacturers offering adjustable bars?

[CTB]

More bends reduce the efficiency of a bar. The best bar is a simple U shape, but of course packaging means that isn't always possible. There are formulas that take all this into account, but you need to take measurements of the car or have the engineering drawing of the bar at your disposal. Today I test drove a 135i and intended on using my calipers to measure the bars. I couldn't even see the rear one when I looked under it, so I didn't get a measurement. Good question about adjustables. H&R shows adjustables on their site in the "glossy" pictures, but that doesn't mean the 1-er bars they offer are adjustable. Anyone know?

[white911]

I found the rear one when I had it on the lift and it appears the entire backend will have to come apart to replace it. But, then I am back to my suggestion to get the right springs and shocks for your driving style and the bar may be perfect.

[Orb]

Originally Posted by BMWeber

Material and condition of that material (heat treating and such) can make a large difference.

Your thinking about the yield strength of steel and that various as you already know. However, modulus is the stiffness of the material and it is very close to the same for all steels. Therefore, making a bar out different steel doesn't make it stiffer.

Orb

[CTB]

Originally Posted by white911

But, then I am back to my suggestion to get the right springs and shocks for your driving style and the bar may be perfect.

Unfortunately, I live in Detroit, home of the worst roads I've seen anywhere in the country. Thus, the right springs are the softest, highest ones; a bar is the only real way to tune the balance without having to increase my dental plan coverage...

[white911]

Pictures of the front and rear bars -- seem not to have worked the first time I tried to post.

Front multiple bends with a really long drop link. It seemed like it could do without the last 90 and shorten the drop link.

You can just see the rear and the drop link. You can even see it behind the spring -- but the rest is hard to follow.

[BMWeber]

looks like the front sway bar on my buddies Jetta that I was just making fun of the other day. better not let him see mine

[CTB]

These pics will come in handy when I go to measure the bars at a dealer. Any good samaritans out there that could measure the bars on their cars with a nice set of calipers?

[larryn]

The backs are the same as the e90 in appearance. They look like a piece of vermicelli. Puny little thing. Only problem is that you have to lower the rear subframe to get access to it for replacement, since it runs over the subframe.

Btw, for you track junkies, that inboard nut on the lower rear suspension arm is attached to an oblong, indexed waher, that allows you to dial in negative camber extremely easily (if you want more rear camber).

[Oregon]

So, what's all the icky stuff dripping everywhere?

[white911]

Originally Posted by Surname

So, what's all the icky stuff dripping everywhere?

It's curious, I did not notice it when I was looking at the suspension and the nice welds on the aluminum pieces. It was not wet or dripping. It looks like some of that spray on corrosion stuff.:iono:

[J-Sud]

might be grease...my VW was packed with that shit...leaked out every summer...yay for Texas heat