[vasillalov]

Hi Everyone,

I am doing some research on rear sway bars for my E90 track car. My car is FBO, caged, gutted with OSGiken LSD and full M3 linkages. I run TCKLine single adjustable coilovers, solid bushings for everything.

I am looking to reduce the understeer that is still present even with the multitude of modifications that are listed above.

So, in doing research I discovered that there are several interesting options for rear sway bars depending on the diameter of the bar. Here is what I've found so far:

OEM:

335i Sedan RSB: 33556764425 D=13MM
335i Vert MSport RSB: 33556764427 D=15MM

M3 Vert RSB: 33552283962 D=23,6MM
M3 Sedan RSB: 33552283655 D=22.5MM
1M Coupe: 33557845522 D=22.5MM

Aftermarket:

CobbTuning RSB: D=15MM
Dinan RSB: D=15.8MM
ECSTuning: D=15MM
H&R RSB: D=20MM


Looks like the Stock 335i RSB is 13MM in diameter which is the smallest and the M3 Convertible RSB is 23.6MM in diameter which is the largest.

Considering that I have full mods + an awesome LSD, I would be looking for something closer to the M3 RSB.


Questions:

1) What's the difference between M3 and 1MCoupe sway bars? Which one fits my car? I know the 1MCoupe is narrower, but it has the same subframe as M3. Also, I know the M3 has a wider track and different geometry than 335i. So, do I get the M3 RSB or the 1MCoupe RSB?

2) Is the M3 Convertible RSB an overkill and create too much oversteer?

3) Is there anyone running H&R RSB on a dedicated track car? What are your impressions?

[feuer]

The differences in the rear sway bars in the vehicles listed above is due to difference vehicle weights (especially in the rear), diferent shocks and diferent spring rates. They should be all interchangeable. Why do you expect larger rear sway bar will remedy the understeer issue your are experiencing? If the rear is easier to rotate is it because the front has more grip or the rear has less grip and will oversteer?

[vasillalov]

I need to get the rear to rotate easier. One way of doing that is to put narrower tires. Another way of doing that is to get a bigger rear sway bar.

The 15mm rear sway bar is designed for cars that do not have LSD and with soft springs. This is not the case with my car as you well know. Running stock sway bars on heavily modified car makes them mismatched to the spring rate and the weight of the vehicle.

I simply want a bit more rotation in the rear that I can control.

[refugeeofwar]

What are your toe and camber settings?

[avocet]

for a dedicated track car I would seriously consider playing with spring rates.

I have a street/occasional track 328i and am going thru the same process as you. I am running a 20mm h/r rsw with a stock front(had a Hotchkis but have found it too stiff) and just acquired a set of swift springs that increase the spring rate considerable(compared to oem sport). With coilovers you should have a big selections of spring rates to play with.

I have just a tad over(under?) -2° of neg front camber(have new plates sitting in a box... looking for -2.5° or more(less?)). Rear camber is pretty tame... -1.7° IIRC

0" toe front/1/8" total toe rear. Might try for 1/16" total rear toe next alignment. I think 0° rear toe might be a little too squirrelly.

[vasillalov]

Originally Posted by avocet

for a dedicated track car I would seriously consider playing with spring rates.

I have a street/occasional track 328i and am going thru the same process as you. I am running a 20mm h/r rsw with a stock front(had a Hotchkis but have found it too stiff) and just acquired a set of swift springs that increase the spring rate considerable(compared to oem sport). With coilovers you should have a big selections of spring rates to play with.

I have just a tad over(under?) -2° of neg front camber(have new plates sitting in a box... looking for -2.5° or more(less?)). Rear camber is pretty tame... -1.7° IIRC

0" toe front/1/8" total toe rear. Might try for 1/16" total rear toe next alignment. I think 0° rear toe might be a little too squirrelly.

I am at -3.5° camber at the front and -2.0° at the rear. I might get either the H&R or the M3 RSB.

Wheel/tire setup?

[Jeff@TopGearSolutions]

I personally run the M3 RSB with UUC FSB but I'm XI on my latest coupe.

I'd recommend the H&R RSB to start since it's not as aggressive as some of those bigger M3 RSB. You don't want to go too far on the RSB if you don't have a matching set in the front.

The sway bars will help keep the camber you specify in your alignment.

-2 is not as advantageous for you in the rear, you may want to try -1.25

[feuer]

So what you want to do is reduce rear grip for car to rotate easier? Is not semantics. You are not fixing the under steer issue with your car that way. At least not properly. If I'm doing it I would look into increasing front end mechanical grip. I honestly don't see how it will make the car go faster around a corner if you are only reducing the rear end mechanical grip. Can someone explain it better?

[mrnuke]

Originally Posted by feuer

So what you want to do is reduce rear grip for car to rotate easier? Is not semantics. You are not fixing the under steer issue with your car that way. At least not properly. If I'm doing it I would look into increasing front end mechanical grip. I honestly don't see how it will make the car go faster around a corner if you are only reducing the rear end mechanical grip. Can someone explain it better?

Basically you're wanting to dumb down the rear end to the front end's level instead of bring the front end up to the rear ends current level. This = lower overall grip instead of increasing overall grip if the front end is working better.

[feuer]

Originally Posted by mrnuke

Basically you're wanting to dumb down the rear end to the front end's level instead of bring the front end up to the rear ends current level. This = lower overall grip instead of increasing overall grip if the front end is working better.

Working better for what? To power slide? I don't think it will result in being able to carry higher speed through corners.

[mrnuke]

Originally Posted by feuer

Working better for what? To power slide? I don't think it will result in being able to carry higher speed through corners.

I am on your side, I should have bolded when you said for someone to try and explain it better.

[vasillalov]

Originally Posted by mrnuke

I am on your side, I should have bolded when you said for someone to try and explain it better.

Guys,

I think you are missing some of the point I am trying to make here. I have a dedicated track car which is still running stock swaybars front and rear.

The 335i OEM swaybars are too soft from the factory because there is no LSD. But I am not driving a stock 335i. Instead mine is fully built, minus sway bars.

Yes, I agree with you entirely. There are multiple ways of "fixing" the understeer. One way is to improve the mechanical grip on the front end. I think I already maxed this option out and I don't think I can do anything else here.

Another way is to reduce the mechanical grip in the rear to make the car more balanced. To do that I can run narrower tires in the back, I can change the spring rate, I can swap the sway bar or I can do a combination of the three.

Right now, if I am mid corner and I apply power, the rear does not rotate at all. There is so much grip in the back that the car starts pushing forward instead of turning. That's not me overdriving it. That's just how the balance is right now. I just want a more balanced car.

Let me see if I can put it in another way:

The M3 Sedan which is about same weight as the 335i has different sway bars, different springs, different suspension components. My car is pretty much M3 suspension wise except for the sway bars.

So now explain to me why I should not get the M3 sway bars?

[avocet]

Originally Posted by feuer

So what you want to do is reduce rear grip for car to rotate easier? Is not semantics. You are not fixing the under steer issue with your car that way. At least not properly. If I'm doing it I would look into increasing front end mechanical grip. I honestly don't see how it will make the car go faster around a corner if you are only reducing the rear end mechanical grip. Can someone explain it better?

It is not reducing grip. It is allowing, or in this case, not allowing, lateral weight transfer in the rear and allowing it to move to the front and allowing the front to transfer the weight and load up and grip.

[cvc 22349a]

M3 F/R sway bars imo. Been a long time since I looked at this stuff but that seemed to be the best combo a few years ago, iirc that H&R rear bar is solid v. M3 is hollow.

[AWDBooSTIn90]

I would highly recommend getting the M3 sedan/coupe Front and Rear Sway bars. They will make a huge difference.

The front end will have much more grip and muchh less understeer and the rear will match the front, with the LSD, just like an M3 has.

The 1M shares the same front and rear subframes as the E90 M3, including the sway bars..

The stock front 335i sway bar tapers down to 3/4 of its size in the center which really reduces its effectiveness, the M3 sway bar does not.

Also like others have said the M3 sway bars are hollow and are very light, but very strong.

I cant believe you have all these mods and DON'T already have front and rear M3 sway bars.

After you do the front and rear m3 sway bars. You can adjust them slightly with poly sway bar bushings or switch to the M3 Convertible Sway Bars Front or Rear or both...

[rismo]

Hi,

I have a similair setup and also not happy with my car handling.

- Full m3 stuff, Drexler LSD, suspension/engine "mounts" replaced with medium hard rubber versions
- M-sport sway in the front
- M3 sway in the back

My issue: I lose traction halfway the corner on my outer rear wheel.

This is caused due to the to stiff rear m3 sway bar.

My plan:

- Chamber plates in the front (More negative chamber)
- Linear spring around and in the rear also stiffer springs
- Replace the rear sway with a normal m- sport sway

With replacing the rear sway back to original I hope to achieve 2 things:

- Bring the car back in balance
- Allow the rear wheels to move more independent

With the more heavy rear springs I hope to keep longer traction on both wheels in the corner avoiding sudden oversteer.

I have learned quite a bit myself form the following two sources:

http://www.racingonthecheap.com/reco...andling-guide/ (Very clear per situation)

and this book:

https://www.amazon.co.uk/Sportscar-K.../dp/1845842073

My adjustments should be finished around the 15th of October and I hope to return to a race track early november before the winter kicks in over here.

Hope this is useful for you..

[rismo]

By the way, sways are the last layer of adjustments, going more heavy is not advicable.
You can drive without a rear sway if your springs and dampers are set correctly.
The lighter the better more or less. When heavy sway are really required you might have other setup issues like again your spring weight.

But to be fair, I have not tuned dozens of cars, I'm more a nerd, looking into the numbers and test configs when I have the opportunity.

[cvc 22349a]

Originally Posted by rismo

Hi,

I have a similair setup and also not happy with my car handling.

- Full m3 stuff, Drexler LSD, suspension/engine "mounts" replaced with medium hard rubber versions
- M-sport sway in the front
- M3 sway in the back

My issue: I lose traction halfway the corner on my outer rear wheel.

This is caused due to the to stiff rear m3 sway bar.

My plan:

- Chamber plates in the front (More negative chamber)
- Linear spring around and in the rear also stiffer springs
- Replace the rear sway with a normal m- sport sway

With replacing the rear sway back to original I hope to achieve 2 things:

- Bring the car back in balance
- Allow the rear wheels to move more independent

With the more heavy rear springs I hope to keep longer traction on both wheels in the corner avoiding sudden oversteer.

I have learned quite a bit myself form the following two sources:

http://www.racingonthecheap.com/reco...andling-guide/ (Very clear per situation)

and this book:

https://www.amazon.co.uk/Sportscar-K.../dp/1845842073

My adjustments should be finished around the 15th of October and I hope to return to a race track early november before the winter kicks in over here.

Hope this is useful for you..

+1 There have been a few track drivers on this forum that have commented the rear loses grip mid turn with the M3 or similar rear bar and have removed them.

[AWDBooSTIn90]

Originally Posted by rismo

Hi,

I have a similair setup and also not happy with my car handling.

- Full m3 stuff, Drexler LSD, suspension/engine "mounts" replaced with medium hard rubber versions
- M-sport sway in the front
- M3 sway in the back

My issue: I lose traction halfway the corner on my outer rear wheel.

This is caused due to the to stiff rear m3 sway bar.

My plan:

- Chamber plates in the front (More negative chamber)
- Linear spring around and in the rear also stiffer springs
- Replace the rear sway with a normal m- sport sway

With replacing the rear sway back to original I hope to achieve 2 things:

- Bring the car back in balance
- Allow the rear wheels to move more independent

With the more heavy rear springs I hope to keep longer traction on both wheels in the corner avoiding sudden oversteer.

I have learned quite a bit myself form the following two sources:

http://www.racingonthecheap.com/reco...andling-guide/ (Very clear per situation)

and this book:

https://www.amazon.co.uk/Sportscar-K.../dp/1845842073

My adjustments should be finished around the 15th of October and I hope to return to a race track early november before the winter kicks in over here.

Hope this is useful for you..

The Msport Front Sway bar also tapers like the 335 front sway bar does also I believe. Why not try a stock M3 front sway bar?

Then you can decide if you want to remove the M3 rear sway bar.

Going from the 335i RSB to the M3 RSB is a big jump in stiffness.

Ive personally liked the M3 FSB & stock RSB combo I am currently running. I dont know if I would change to an M3 RSB without trying out stiffer rear springs first. The back end seems to come out when I want it too, under heavy steering and then applying a decent amount of power. Plus the car barely understeers with the M3 front control arms and M3 FSB.

I would say for faster track times, hold off on going immediately to a stiffer RSB.

For fun, put in the E90 M3 RSB with the front for some sideways action more easily and often. It also depends on driving style and type of driving/track setup you're doing as well. Considering the RSB is not a quick swap like the front Sway Bar is, I could see the appeal of possibly going for an aftermarket adjustable RSB that has multiple mounting positions for the end links, for dialing in the rear without having to change it out...

[rismo]

I think if you look on the info below, which I stole from ORB, at this link

https://www.e90post.com/forums/showp...1&postcount=10

You see the difference between the M3 oem spring rates and the e9x non M 335, (Orb did not include the M-sport versions (eu/us) but it's somewhere in this forum).

You see a big difference in spring stiffness. Also front - rear ratio is significant different, M is almost factor 4.
Anyhow, to be honest I'm not completly sure why M went with both stiffer springs and sways. Stiffer springs I can imagine. But the more heavy sways, I can only guess, it might be a good fit for our chassis.

I'm also not sure if they are progressive or linear.

The message from Orb:

The motion ratio for the car:

• Front: 0.96^2
• Rear: 0.563^2

Calculation for wheel rates:

Coil spring rate * Motion ratio = Wheel spring rate

Stock 335i example.....

E.g. 145lb/in * 0.96^2 = 134 lb/in
E.g. 460 lb/in * 0.563^2 = 146 lb/in

Spring rates:

Stock 135i:

• Front: 120 lb/in
• Rear : 350 lb/in

Stock 335i e92:

• Front: 145 lb/in
• Rear: 460 lb/in

Stock M3 e92:

• Front: 160 lb/in
• Rear: 550 lb/in

335i KW v3:

• Front: 260 lb/in (progressive average)
• Rear: 570 lb/in

335i KW Clubsport:

• Front: 400 lb/in
• Rear: 570 lb/in

M3 KW v3:

• Front: 285 lb/in
• Rear: 630 lb/in

M3 KW Clubsport:

• Front: 508 lb/in
• Rear: 800 lb/in

335i Bilstein PSS10:

• Front: 385 lb/in
• Rear: 615 lb/in

Orb’s 335i:

• Front: 336 lb/in;
• Rear: 672 lb/in;

To scale the OEM suspension frequencies you can use this formula to get a rear spring rate.

(New front spring rate/OEM front spring rate) * OEM rear spring rate = new rear spring rate

E.g. (265 lb/in /145 lb/in) * 460 lb/in = 840 lb/in

If you do the calculation you will see the rear spring is really soft in these performance setups. Soft ass end means more understeer! Kind of makes one wonder if anyone is telling the truth that thier car is all that great!

End of copy...
------------------

I'm still looking for the exact m-sport spring rate and sways. Will get back to that one.

[rismo]

Originally Posted by AWDBooSTIn90

The Msport Front Sway bar also tapers like the 335 front sway bar does also I believe. Why not try a stock M3 front sway bar?

Then you can decide if you want to remove the M3 rear sway bar.

Going from the 335i RSB to the M3 RSB is a big jump in stiffness.

Ive personally liked the M3 FSB & stock RSB combo I am currently running. I dont know if I would change to an M3 RSB without trying out stiffer rear springs first. The back end seems to come out when I want it too, under heavy steering and then applying a decent amount of power. Plus the car barely understeers with the M3 front control arms and M3 FSB.

I would say for faster track times, hold off on going immediately to a stiffer RSB.

For fun, put in the E90 M3 RSB with the front for some sideways action more easily and often. It also depends on driving style and type of driving/track setup you're doing as well. Considering the RSB is not a quick swap like the front Sway Bar is, I could see the appeal of possibly going for an aftermarket adjustable RSB that has multiple mounting positions for the end links, for dialing in the rear without having to change it out...

I was actually thinking about the same, however I want to understand why BMW does not apply that ratio themselves and went for a heavy rear sway and springs.