Let me first start off by saying Iím not extremely technical but I do have some suspension experience with my E46, sport bikes and spend a good bit of time at the track supporting various friends both car and motorcycle. My E46 was fairly highly modded. In terms of suspension I had: UUC sways, Ground Control bits, RSM etc, and Bilstein PSS9s. When I purchased my M3 I was very unhappy esthetically with the wheel gap. At the time, I decided to purchase lowering springs with the intent of purchasing a coilover suspension once the market matured a bit and there were products I felt were a large performance increase over the stock suspension.
I purchased the H&R sport plus springs which interestingly are sometimes called race version and on H&Rs website it lists them as the race part number from EAS. These springs claimed a 1 inch front drop and .6 in the rear. I actually think itís slightly more than that in the front. The race springs have a higher spring rate and are progressive. They donít publish rate so itís hard to know what they really are and since itís non-linear Iím not sure how much help it would be. I can say visually it made the car much more appealing. The ride was firm but really not a problem for me. I daily drive the car about 90 miles a day and pretty much always leave the edc set for sport. Well, Iíve had the springs for about 2.5 or so years and now the car has 65k on it and I can feel the stock dampers starting to go.
I launched into a pretty exhaustive search about which coilovers to switch to based on some great information like rldzhaoís thread
and then various reviews of KW, AST, Moton, Ground Control, TC Kline etc. I must say there are some outstanding threads contributed by members with excellent information. I really needed a quality suspension without a crazy rebuild cycle. I needed a suspension that wouldnít kill me during daily use. I wanted a suspension I could use for some track days and that was a performance upgrade from stock. The biggest ďchallengeĒ is that there are many quality suspensions available for our cars and the suspension ride quality is very subjective.
I had kind of committed to a double adjustable or triple because I felt the flexibility of individual compression and rebound adjustments would allow me to dial the suspension in to better suit my needs. At this point, I contacted Harold from HP Autowerks. Harold suggested the TCK DAs paired with Swift springs. I had been strongly leaning toward ASTs but Harold felt the design of the dampers vs the monotube design of the ASTs would allow for a more compliant street driving experience. I decided on 728lb rears with 448lb fronts.
Also included in my setup are Vorshlag camber plates, HPA adjustable sway bar links and Swift springs and thrust sheets. Haroldís customer service has been outstanding dealing with about 20 different questions I had. I would highly recommend him. Tomorrow, I have new tint being installed and the car goes the GT Performance here in Maryland on Friday for install. Check back for pictures and a review to follow.
Fairly current look with H&Rs for reference: