Quote:
Originally Posted by jhnmdahl
I'll chip in late to this, having just installed Bilstein B8 + Eibach's springs (E10-20-031-06-22) on a 340ix. The car came with almost every option but had a standard suspension (168 lb/in front and 486 lb/in rear), while the Eibachs stiffened it about 20% to 194 in/lb and 542 in/lb (it is far more than the 10% stiffer that people keep repeating, unless you're upgrading from a sport suspension). The car felt underdamped to me before any work, so I also installed Bistein B8 shocks at the same time. Plus, more than one person on here has done Eibach springs only, and commented that they regretted not doing shocks at the same time due to it being underdamped.
Installation went smoothly, and I'd recommend a pass-through socket set with universal sockets (Craftsman has a decent 58 piece one that can be found for $50) for things like the reverse Torx-head bolts and sway bar link removal if you don't already have one. Predicted drop of .8 inches in front and .6 inches in back appears to be about what I observed.
Driving, the car no longer feels floaty and bouncy, and feels more agile. I don't care about "stance" or having a "sick look" as much as not scraping the ground like I did with my 330XI with H&R springs, and I'm pretty pleased with the Eibachs. The upgrade is exactly what I had hoped for - nothing extreme that would keep people from wanting to ride in my car, but turned it into a sporty sedan that handles well so it no longer feels like a Lexus.
Other options -
Dinan is a bit stiffer at 225 in/lb front and 668 in/lb at the rear with about .7" drop front and rear, but I don't think I need additional stiffness or drop after driving the Eibachs.
H&R (28832-1) drops about 1.5 inches in the front and in the rear, and although they don't have linear spring rates they use a 54SiCr6 spring steel that is quite stiff - starting about 15% stiffer than factory standard springs (about the same as Eibach) and becoming quickly progressively stiffer. Almost certainly more than I want given they have to compensate for the substantial drop in height with additional stiffness.
Sport springs (BMW) are about halfway between the Eibachs and the standard factory suspension, and not hard to find used due to other people upgrading. I figured I didn't want to go through all the time and expense of putting in a new suspension for such a potentially minor improvement, and I'm glad I didn't.
John
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Good info and impressions! It's always nice to see a calculated approach with specs/numbers to achieve functional ride/handling goals.
Where did you see the spring rates for your OE front/rear springs? The data I've seen said the 340ix came stock with 143lbs/in front and 426lbs/in rear springs and with the adaptive M suspension 174lbs/in front and 518lbs/in rear.
I've never seen then numbers for the Dinan kit before, but those spring rates are about equal to the 335/340i RWD M-Perf springs front and rear. With those rates the car might be close to a pitching frequency regime...