Well, there are already some aftermarket suspension out there for the E90, and although BMW come with great handling cars from the factory, a simple spring/shock change can turn a great handling car into a sick handling car
I tried to compile it all into one list for now so we can all use it for reference.. hope this helps, and if anyone has suggestions or finds new products please post them here, it would help everyone out !
For those that don't know, its always better to get a matched spring/shock set for a car in terms of handling performance, ie. a coilover set will be better then just springs, but it may also be overkill for the street, depending on what you use your car for..
I'll try to organize these by the amount of lowering they offer from least agressive to most agressive.
ALL LOWERING MEASUREMENTS ARE BASED ON THE STANDARD SUSPENSION, NOT SPORTS SUSPENSION. Obviously, if you have the sports suspension, then these options will lower the car a bit less then listed here.
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Springs:
0.6" --> OEM Stock BMW Sports Suspension
1.2" / 1.0" --> Eibach Pro-Kit (part # 2085.140)
1.2" / ???? --> KW Automotive Springs (part # 25020058)
1.2" / ???? --> Hartge Sport Springs
1.3" / 1.2" --> H&R Sport Springs (part # 50490)
1.35" / 0.8" --> H&R Sport Springs (part # 29187-1)
(** Europe-Part# ** this is aparently the same spring as the 50490 but with different lowering listings for some reason.)
1.57" / 1.3" --> Hamann Progressive Springs (part #20 090 120)
1.8" / 0.8" --> H&R Race Springs (part # 29183-1)
(** Europe only **)
2.0" / 1.4" --> Eibach Sportline (part # 4.0285)
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Shocks only:
Non-adjustable Shocks:
Bilstein B12 Tuning kit shocks (part # SE5-C043) -- Lowering Range--> 35mm
Bilstein B6 sport shocks (part # VE3-C037 / VE3-C038) -- Lowering Range --> retains stock height
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Matched Sets/Coilover Sets:
Non-adjustable Matched Springs+Shocks:
Eibach Pro-system (part # 70-20-014-02-22) -- Lowering range--> Front/Rear: 1.2"
Height Adjustable:
KW Variant 1 coilovers (part # 10220032) -- Lowering range--> Front: 1.2-2.3" Rear: 0.9-2.1"
H&R Coilovers (part # 29177-1) -- Lowering range--> Front: 1.58-2.78" Rear: 1.19-2.38"
Eibach Prostreet-S (part # 65-20-014-01-22) -- Lowering range--> Front: 1.38-2.57" Rear: 1.38-2.57"
Bilstein B14 PSS coilover (part # HE5-C047) -- Lowering range--> 30-50mm
Hamann Coilovers (part # 20 090 105) -- Lowering range--> Front: up to 2.36" Rear: up to 1.57"
Height Adjustable + Rebound Adjustable Dampening:
KW Variant 2 coilovers (part # 15220032) -- Lowering range--> Front: 1.2-2.3" Rear: 0.9-2.1"
Height Adjustable + Rebound Adjustable + Compression Adjustable Dampening:
KW Variant 3 coilovers (part # 35220032) -- Lowering range--> Front: 1.2-2.3" Rear: 0.9-2.1"
Bilstein B16 PSS9 coilover (part # GM5-C051) -- Lowering range--> 30-50mm
Bilstein B16 PSS10 coilover (part #GM5-D163-H1)
HKS Hipermax III (part # 80140-BE001)
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Anti-roll bars:
BMW Stock ZSP: 26.5mm (38291 mm^4) /13mm (2803 mm^4)
Biasing: 93% / 7%
BMW Stock M3: 26.5mm (39310 mm^4) /22.8mm (12904 mm^4)
Biasing: 75% / 25%
BMW Stock e93 M3: 28mm (46380 mm^4) /23.6mm (23000 mm^4)
Biasing: 67% / 33%
Eibach: 28mm (60343 mm^4)/ 15mm (4970 mm^4) (part # 2085.320)
Biasing: 92% / 8%
H&R: 27mm (52714 mm^4)/ 20mm (15707 mm^4) (part # 33211-1)
Biasing: 70% / 30%
Hotchkis: 32mm (75961 mm^4)/ 16mm (6433 mm^4) hollow bars (part # 22834)
Biasing: 92% / 8%
Dinan: 28mm (60343 mm^4)/ 15mm (4970 mm^4) (Front Part #D120-0510, Rear Part #D120-0515)
Biasing: 92% / 8%
UUC (first batch): 27mm (52714 mm^4)/ 19mm (12794 mm^4)
Biasing: 75% / 25%
UUC (Second batch): 28mm (60343 mm^4)/ 19mm (12794 mm^4)
Biasing: 82% / 18%
BMW Stock ZSP Front with BMW M Sport Rear Sway: 26.7mm (39310 mm^4) /14mm (3771 mm^4)
Biasing: 90.5% / 9.5%
BMW Stock Xi or e93: 26.7mm (38291 mm^4) /15mm (4970 mm^4)
Biasing: 89% / 11%