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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > Koni FSD, B&G S2 springs, E93 M3 rear sway bar, etc. on my E92 335xi



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      07-05-2016, 02:39 PM   #1
AtlasM
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Koni FSD, B&G S2 springs, E93 M3 rear sway bar, etc. on my E92 335xi

After a delay of this project due to UUC sway bars being back ordered, I've now got my new suspension on my 2011 335i xDrive coupe. So far I'm extremely happy with the drop from the BG springs, I spent a long time agonizing over photos of the drop from Eibach & H&R and these seemed like the best to me.





Initial impressions:

Ride quality is pretty damn close to the soft xDrive stock suspension, but way less floaty. It may actually be a bit better over some bumps. There's a small additional amount of NVH on grooved concrete, probably from some the firmer bushings or end links. Occasionally it gives a sensation of "hovering" over certain kinds of bumps, but not in a bad way, more like the car is keeping the wheels planted on the ground while controlling body motions very well.

Cornering is a noticeable, if not earth-shattering improvement. The front end has a lot more grip and it stays much more planted in turns. Initial turn-in bite is improved, although not drastically, and the xDrive steering ratio is still slower than I'd like. I still need to get an alignment, and I'm going to shoot for something like 2.5 to 3 degrees of negative camber in the front plus as much positive caster as they can get out of it. So turn-in may be further improved from getting the right alignment.

Excess ride motions like brake dive, and head toss during shifts, are also very much reduced. On the stock suspension the car had a tendency to squat down on the rear and raise the front while accelerating out of tight turns, and that is mostly eliminated.

Overall the handling is much more planted and confidence-inspiring but doesn't scream "modified car," more just nicely sorted.

Tires are Kumho Ecsta PS91 235/35-19 front, 275/30-19 rear. I was pretty sure I really liked the tires on the stock suspension but it was a little hard to tell. Now I for sure really like these tires. The wheels are Advanti DST Catalan 19x8.5" +32 and 19x9.5" +32. They're relatively not-crazy-expensive flow-formed wheels available from Tire Rack, and weigh about 21-22 lbs per wheel. I've had a bit of rubbing (I think on the struts) with these wheels on both the stock and lowered suspension. Mostly in the front. Once the car settles and it's aligned I'm going to measure for spacers. Nothing too aggressive, especially in the rear since I'm already pretty flush with the fender lips there.

Parts list:

B&G S2 lowering springs (08.1.166)
Koni FSD shocks (2100 4123)
E36 M3 front bump stops (31332225377)
E85 Z4 M rear bump stops (33507836826)
Ground Control E90 xi street camber plates
Ground Control front adjustable sway bar end links
Hotchkis rear adjustable sway bar end links (25834R)
Seals-It rod end boots (RERS-2) - these ended up only fitting the Hotchkis rod ends, not Ground Control
Strongflex front tension strut bushings (031528B) x2
Strongflex red front sway bar bushings (031248B 26.5mm) x2
Whiteline rear subframe bushings (KDT917)
E93 M3 23.6 mm rear sway bar (33552283962)
E93 M3 rear sway bar bottom bushings (33552283709) x2
E93 M3 rear sway bar top bushings (33552283710) x2
E93 M3 rear sway bar bushing brackets (33552283714) x2
E93 M3 rear sway bar bolts (07119906077) x4
BMW front upper spring pads (31336767500) x2
BMW front lower spring pads (31336764372) x2
BMW front dust boots (31331094749) x2
BMW rear upper spring pads (33536764419) x2
BMW rear lower spring pads (33536764420) x2
Monroe rear upper shock mounts (907984) x2
Monroe rear lower shock mounts (907985) x2

Last edited by AtlasM; 07-05-2016 at 02:44 PM.
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      07-05-2016, 06:41 PM   #2
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Car looks great btw, love the color! Wish I had it. I've looked over your parts list and begin to wonder why you put on so much because the feedback I am getting is that it made a difference but not earth shattering. Was it really worth it? I figure go with coil overs and be pretty much done. How much better can we get our cars is the question. We keep spending for this and for that but at the end of the day is it a track beast or a very good daily driver? I'm just trying to figure out and justify my new suspension on what to do really. I'm thinking Bilstein (?)/Eibach...maybe sway bars down the road. The other stuff I have no clue about...control arms, bushings, bump stops, etc. WTF! I just don't know enough about this stuff to even contemplate anything more than the basics. Need your feedback on everything if you could...
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      07-05-2016, 08:07 PM   #3
AtlasM
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When I say "not earth shattering" I mean that the car didn't suddenly transform into the handling abilities of a Lotus Elise. But there are lots of different improvements in different aspects that fall under "handling." Add them all together I would call the improvement pretty significant though. It's subtle, because going down the road, the overall comfort feels very much similar to before. It's only when I chuck it into a turn does it get noticeable.

But even stuff like the reduced brake dive and head toss while shifting is noticeable. On the stock suspension, just driving around town, my fiancee complained about the car rocking back and forth when I'd shift, and I like to think I'm pretty good at shifting.

Part of the reason the parts list is so long is I did all new stuff to go with the shocks and springs. But spring pads and dust boots are all pretty minor cost wise.
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      07-06-2016, 03:15 PM   #4
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So to give you a bit more of a breakdown, all this stuff is just to have fresh parts when installing the shocks & springs:

BMW front upper spring pads (31336767500) x2
BMW front lower spring pads (31336764372) x2
BMW front dust boots (31331094749) x2
BMW rear upper spring pads (33536764419) x2
BMW rear lower spring pads (33536764420) x2
Monroe rear upper shock mounts (907984) x2
Monroe rear lower shock mounts (907985) x2

The stock rear shock mounts are weak and the Monroe pieces have harder rubber, which is why I went for those.

If you're going with lowering springs on Koni shocks, you should use shorter bump stops, E36 M3 front and Z4 M rear. This is because lowering springs reduce your suspension travel and give your shocks less room to work. By going to shorter bump stops, you get back some of the suspension travel you lose from lowering. I believe Bilstein shocks have integrated bump stops but I'm not 100% on this.

Adjustable sway bar end links are because lowering the car changes the orientation of the sway bar with the rest of the car. On a lowered car, in order to get the sway bar back in its desired position with the sway bar end parallel to the ground, you need longer end links in front and shorter in rear. You can run stock end links but it's not ideal.

Changing the rear sway bar requires dropping the rear subframe. This is a non-trivial process. Replacing the subframe bushings at the same time is good so you don't have to drop the subframe twice. The stock subframe bushings are too mushy and soft and allow the back end of the car to bounce around too much.

The front tension strut bushings are to help improve steering feel, because the stock front tension struts have a hydro bearing type "bushing" that allows too much slop in that part of the suspension. This is why on the rwd cars, people switch to M3 front lower control arms, but those don't fit on the awd cars. The options available for awd cars are Strongflex bushings (they offer two different hardness levels) and Syncro Design custom control arms.

I put poly bushings on my stock front sway bar because in going for a stiffer rear sway bar, I wanted to get the most possible effectiveness out of my stock front sway bar. The bushings are a small improvement but they help the front sway bar do its job a little better.

Camber plates are to dial in a specific amount of negative camber in the front. Lowering the car gives you some negative camber anyway but I wanted to have the car fully aligned. You don't necessarily need them, or a cheaper option is the Dinan fixed camber plates that re-use the stock upper shock mounts.

I chose B&G springs when everyone seems to talk about Eibach or H&R as the only choices, because I didn't really like how the drop from Eibach and H&R looked. To me, all the pictures I saw of the H&R xi-specific springs lowered the car a little too much in the rear and not quite enough in the front, and many people complain about their stiff ride. Eibach looked alright but I figured I could go with a bit more lowering. B&G are supposedly a little stiffer and lower than Eibach but not nearly as stiff as H&R. Personally, I think the drop I got out of them is just about perfect. I took these pics only a couple days after the suspension was put on so it may settle a bit more.

I went with the E93 M3 rear sway bar because I wanted to reduce overall body roll and get the car to rotate a bit more while powering out of a turn, while not making the car too tail-happy. The E93 M3 23.6 mm bar is the thickest BMW OEM hollow sway bar for our platform, whereas the aftermarket solid bars, even those that are thinner like 19 or 20 mm, are significantly stiffer than the E93 M3 bar. I was worried that those bars might make the rear end too loose. The list of parts for the E93 M3 rear sway bar looks long because I listed every single bushing, bracket, and bolt needed to put it on the car.

I still need an alignment to get the camber and other things dialed in but as it is right now, the front end has a lot more grip and stays way more planted than before, the car rotates nicely with power on corner exit but is not overly tail-happy, and body roll is reduced, but not eliminated. All while there is essentially no increase in ride harshness.

If you're looking to do a first step improvement that's not as much of a project, you can just do shocks and springs, and not worry about the bushings, camber plates, sway bar, etc. You can in theory reuse the spring pads, dust boots, and shock mounts but I decided to replace all those because they're cheap and the Monroe rear shock mounts do a better job of keeping the shock solidly mounted. I would at the very least still go with the E36 M3/Z4M bump stops, and adjustable sway bar end links.
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      07-07-2016, 10:59 AM   #5
AtlasM
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Cleaned up the car and got out my good camera instead of my phone. Very happy with the ride height!

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      07-07-2016, 11:05 AM   #6
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Quote:
Originally Posted by AtlasM View Post
Cleaned up the car and got out my good camera instead of my phone. Very happy with the ride height!

Car looks perfect imo. Ride height is spot on. I still want your car...
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