Long post below. TL;DR: Good street coilover that would likely do well on track. Don't expect a high end track setup. Won't go very low.
Finished pic first:
Ever since we were ordering my wife's F31, I was thinking that I would not be very happy with the suspension and would need to upgrade it. The US spec F31s only came in xDrive, and xDrive vehicles do not get a sport suspension setup. So knowing that I was going to swap out the standard xDrive suspension, we ordered the car without DHP. This is our street car, and won't see any regular track time. I might do a parade day or a few autocrosses, but track use was not a deciding factor for picking the setup.
Background and experience: This is our 4th 3 series, we have an E36, E90, this F31, and recently sold our E46. I do about 6-10 track events a year in my E36 track beater which have "high end" MCS dampers with Vorshlag and Hyperco hardware. My E90 has PSS10s, and I've been pretty happy with them - my old review here:
http://www.e90post.com/forums/showthread.php?p=6062243. Our E46 was a DD that had stock sport suspension that was not modified.
There simply were not many options for F31s due to the xDrive platform and the heavier wagon. There are some spring / shock combos out there, but I was not particularly interested as they often had weird lowering ranges (typically lowering the front of the car more), and even fewer F31 specific applications. I was pretty set on a coilover setup for the height adjustability, and damping adjustability. It's my wife's car so it can't be too low or stiff - she's not a car person so a more "regular" setup was important here.
It came down to a few choices: KW's V1/V2/Street Comfort, and Bilstein's B14 PSS/B16 PSS10. There are other KW alternatives but I was not interested in double adjustable dampers and the like for a street car. I'm biased towards Bilsteins as I've had them in numerous cars before without ANY issues. They're much more convenient to revalve, although their lead times have increased to weeks instead of days for a revalve now. The process to revalve KWs is a pain based on my friend's recent experience (took 11 weeks from door to door, when promised 6-8 weeks). I also prefer Bilstein's monotube dampers over KW's twin tube design - I just like the feel of them better. Finally, KW's F31 coilovers have had issues with rear springs that were too short and it required using a spring spacer to get the correct ride height. It looks like KW recently came out with a 2-part spring that alleviates this issue based on what I've read here.
Either way, I decided to go Bilstein and had to choose between PSS and PSS10. I actually had the Bilstein PSS coilovers on my E36 when it was a street car - and it rode pretty darn stiff. They used springs that were somewhat soft - 400F/425R lb/in respectively, but they were just valved stiff. While I was fine with that, I figured my wife would be bitching about it if the F3x application was the same (a few users here reported a stiff ride with the B14 PSS setup). In contrast, the PSS10s on my E90 were nearly as soft as the factory sports suspension at the softest setting, that I hoped the F3x application would be similar. So PSS10s it was. Note: Bilstein does not make a specific kit for each F30/F31/F32/F33/F34 etc. body styles. 1 part number for all xDrive F3x cars. Therefore, the spring rates are not be fully optimized for each chassis. I took the chance that it would work well on the F31.
The xDrive PSS10s might be pretty new at the time of this writing, as most supporting vendors here were unable to get an ETA or did not show availability at all for them. I was able to go through a vendor I've used many times in the past to get a set from Germany. They're not sponsors here so I won't mention them. In time, I believe this will be a non-issue so check with sponsoring vendors for a set.
The setup arrived quickly and a couple quick notes about the kit:
- Generally good quality as expected from Bilstein. Everything is machined well with good fit and finish.
- Damping adjustment has good tactile feel, important as you won't easily see them when you adjust.
- The rear shocks are inverted - the shaft which normally connects to the body, is connected to the control arm. This is pretty smart as it puts the damping adjuster at the control arm. My E90 setup was not like this and required a lot more effort to install, and also required cutting the interior carpet in the trunk to access the damping adjuster.
- The rear spring height adjuster does not have 2 perches that lock together to prevent movement. There isn't rotational force on a rear spring unlike the front Macpherson setup so it doesn't really need it I guess. My E90 had locking perches.
- The spring perches have holes for the adjusting wrenches instead of notches. I much prefer the holes as it's harder for the wrench to slip off.
- Bump stops are built in and dust boots already installed, no need to re-use OEM ones. NOTE: upon actually looking at the instructions, they state to cut the top 40mm of the front strut boot and re-use. I believe this is to prevent dust from getting to the strut mount, not into the strut. I didn't do this as I didn't know instructions were there. I'll report back of my strut mounts die early.
I've installed plenty of suspension setups so I tackled this myself over the weekend. I purposely didn't tell my wife to see if she would even notice a difference. I was caught red-handed when she arrived home early and I had the front end completely torn apart.
She was like WTF are you doing to my car?? Um... rotating tires...?
No truly "special" tools required. Spring compressors, pass-through wrenches, and e-torx sockets will be required, and they can be considered special tools depending on the size of your toolbox.
I used some great install notes from
wwmiller3 here:
http://f30.bimmerpost.com/forums/sho....php?t=1138911. Pay particular attention to #5 and #6. I'll add my 2 cents on those later.
Installation was pretty standard affair. If you've done suspension installs on other cars before then you won't have too much trouble here. I wasn't planning to do a big DIY, there are plenty of threads on the forum that cover that. I'll just note anything to be careful of or PSS10 specific.
- Tape the fenders on the front. It's easy to scratch them maneuvering the strut in and out of the wheel well.
- The front struts are held into a collar, pinched together by a bolt. You have to spread the collar, to remove the whole strut assembly. There's a lot of ways to do this. Mine: Take a pry bar and pry the collar apart just a bit, enough to fit a shitty 7mm hex drive into the collar. Rotate the 7mm hex drive 30 degrees so it spreads the collar. You'll have enough room to easily wiggle the strut out. You'll ruin the shitty 7mm hex drive bit.
- RE: wwmiller3's top hat reference (#5): The xDrive springs are TALL. You'll need to compress them a lot to relieve them of pressure to unbolt the strut's top hat. As you get them compressed, they start bending a bit and put a sideways force on the top hat. This can cause the top hat to split open, blasting bearings everywhere.
- RE: wwmiller3's axle reference (#6): The axle WILL come out of the differential when you swing the strut out of the fronts. Don't worry, it's easy to get back in. As you start to push the whole front assembly back under the wheel well, slowly rotate the brake rotor. This will spin the axle and when the splines line up they will slot right back in.
- Take out the rear spring by removing the lower control arm bolt close to the brake rotor. Relieve pressure on the bolt by jacking up the control arm basically all the way up. Re-aligning the hole to get this bolt back in is the hardest part of the install.
- On the rear shocks, Bilstein painted over the threads where the top nut goes on - shame on them. This makes it nearly impossible to get the nut on. Wire brush the paint off the threads.
- The front height adjustment is easy with tons of room to adjust. The rear height adjustment is ridiculous to adjust. Everything is in the way of the wrench. The best way is to loosen the felt wheel well (1 screw and 1 nut) so that it can flap about. Then you can turn the wrench 30 degrees at a time. You'll have to reposition the wrench 6 times to get 1 rotation of the spring perch.
- I usually start with coilovers at the highest position as it's easier to relieve tension than add tension. Don't do this for the rears (see above). Start with 8 full rotations from the highest position. That's 1" lower than stock. Reference: 14 turns down from the top is 1" lower for the fronts.
- If you don't want to use a spring compressor, or if your strut mounts are old, buy 2 new top hats and just install them onto the coilovers. This way you can take your OEM struts out complete and just set them aside without disassembling them. I would do this in the future to save 40 minute on install time, and if I have to revalve my Bilsteins, it's easier to reinstall my old setup to drive in the mean time.
- Total install time was about 6 hours by myself. I was a jackass and started late so I didn't use power tools as to not wake the neighbors. A buddy and power tools should make things quicker. Fine tuning of the height multiple times, and playing with settings probably took an additional 2 hours the next day.
- Take 1 extra minute to clean the calipers if you have pretty brakes.
- No noises, squeaks, creaks, rattles, or groans after install.
A special note about ride height. If you have the spring perches adjusted all the way up, it's actually higher than the factory xDrive setup. This kit will not slam your car, #stancenation guys will have to look elsewhere. The front ride height in the following photo is a hair high. I adjusted them down just a tiny bit after these pics.
On the road. You will notice that the car rides stiffer even on the softest setting. I think it's stiffer than F30s with sport suspension (RWD cars). It's comfortable enough for daily driving unless you're really old. I'm just starting to get old, so I'm OK with it. I then tried settings 3, 5, 6 and 8 (higher numbers are stiffer). Just 2 clicks up at 3, it's starting to get to the upper limit of DD comfort. Completely liveable, and if you want a firmer ride with a little less wallow, 3 is a decent setting all around. I'd call 5-6 a good canyon carving setting. Increased rebound and compression is nice to control the corners a bit better, and compliant enough to handle undulating roads. 8 is way stiff, stiffer than what most people need on the street I think. I never even got to 10. If you're going to do a few track days, the upper ranges will work better, and you can tune out some under/oversteer with different settings F/R. I left it at the softest setting of 1, it'll do great there on the mean commutes of the SF Bay Area.
Adjusting the dampers are easily done in 2 minutes, although you have to get on the ground. Turn the front wheels and you can easily access the fronts. The rears you just give her a reach around and feel for the knob and tinker with it.
Out in the twisties you immediately notice the springs are waaaayyyy stiffer than the xDrive ones. That's a good thing for most. I didn't bother to contact Bilstein about spring rates, don't really care about specifics for a street car. But the body roll is considerably less and the door mirrors are no longer scraping the pavement on corners. Left/Right transitions are handled well and it's just more nimble all around. It doesn't negate the huge amount of weight being thrown around with this boat of a wagon, but it does a good job controlling overall body movement. The terrible steering feel of the F3x remains terrible.
I didn't go crazy on public roads, but with the same numerical damper settings front and rear, the car still tends to understeer in steady state, slow cornering. The car does have staggered tires, but the tendency is still there. Without going to the track, it would be hard to tell how it really does. I could imagine running something like 8F/10R or something similar on track to dial out some understeer (pure speculation at this point). Maybe I'll sneak the car out to an autoX or track day soon to confirm. For occasional track days, I think the kit will work out fine too. I'd say if you do less than 4 events a year, this would be adequate (although stock is adequate too if you really think about it).
If you're building a track car, look elsewhere and heck, get a RWD car to start with. xDrive is just the wrong car to start a track car with IMO.
I'll update this thread with alignment specs and corner weights when I get them. I was pretty careful about lowering each corner the exact same amount to maintain the stock weight distribution. On my E36 and my E90, that has served me well and both those cars have 49.x% or 50.x% cross weights when I went in to corner balance them. Essentially, I didn't corner balance them since they were already spot on.
Finally, for shits and giggles, I took the Apex ARC-8 wheels from my E90 and test fitted them on the F31. They're square 18"x9.5" ET35 wheels, with 265/35/18 Dunlop Direzza ZIIs on them. The tires run super wide, wider than some 275s. They clear everything on the inside of the car, but if I drove the car I'm sure it would rub really bad all along the fenders. And these were shorter tires than the F3x size, a slightly taller and narrower 255/40/18 might fit nicely instead. Maybe I'll get new wheels for my E90 and put these on the F31. Doesn't look bad, although the front was still a hair high in this picture, it's been adjusted a bit lower.
Oh and when the wife drove it... "I don't notice any difference. At all."
