[johnung]

Originally Posted by Alpine_F30

Damn that first car is dope! :P

Couple things to note...

1. The angle of the picture, distance it's taken from, etc. will greatly affect how you're perceiving the ride height in a photo! For example, the first picture appears a little deceivingly low from that angle, also it's a slight downhill slope.
2. Many Xdrive versions of springs will sit a little higher, especially in the front, than RWD. I've seen many disappointed people who installed Dinan springs on their XDrive only to see their car still have a ton of wheel gap up front because they were looking at photos of RWD cars.
3. There's also some minor drop variation between models (ie. RWD Dinan 335i = 3/4" drop, 328 = 1" drop, etc.)
4. The tire size and wheel offset will also effect how low the car appears. Stick with meatier tire setups to minimize wheel gap when lowering on springs, and potentially look into spacers of lower wheel offset to fill out fender.

Drop-wise I think the H&R sports are pretty close to perfect, and this is from someone who had Dinans on RWD and was happy with them, but wanted to go lower. For a subtle drop Dinan, ACS, and Eibach are all pretty much the same, lowering the car ~1in. or less and giving a slightly more aggressive stance. H&R sports take it ~1/2" lower than the above, which looks as close to perfect to most people without going to coils/bags.

Wondering if anyone's done Swift springs on stock struts on the F30...

Excellent points!
BMW engineered Xdrives to have a natural reverse rake where the wheel gap in front is higher than in the rear. Eibach springs for xdrive are nice because they get rid of a lot of that reverse rake. Front drop is 0.8", rear is 0.6".

I did not want to drop my Xdrive by 1.5" for fear that I'd get into limits of suspension geometry and cause myself problems. Plus I'm in a snow climate and don't want it any lower. In my own testing, moderately dropped on Eibachs it can still handle 6 inches of new snow without getting stuck.

Good point about sidewall height affects on wheel gap. For instance, going from a stock 225/45-18 to a 245/45-18 will fill wheel gap so car appears dropped without doing so. To calculate actual wheel gap don't go by sidewall markings. TireRack lists actual tire diameter measurements in Specifications tab for each model/size of tire.

[FaRKle!]

Originally Posted by johnung

Correct!
B4 = OEM
B6 = heavier duty than OEM
Both B4 & B6 are supposed to be used with stock height springs, but at the same time Bilstein claims they can handle up to a 40mm drop which is 1.5".

Personally I'd use:
Stock springs: B4/B6
Moderate drop springs, 3/4": B6/B8
Full drop springs, 1-1.5": B8

I characterize it a bit differently:
B4: OE-ish levels of dampening (but you don't know which model or base/M-sport suspension the damping is based off of).
B6/B8: Over damped, even with stiffer springs (provides "tight" ride feeling and body control at the expense of increased harshness and lower grip over very bumpy surfaces).

I don't recommend B6 front struts for lowered vehicles, but the rears are OK. Even with the recommended Eibach springs for my vehicle (where the drop is considered light to moderate by most standards) the internal bump stops were already engaged at static ride height. The B6 stops are pretty soft, so it wasn't jarring, but still not optimal.