[KevinK2]

"..Eibach has used the V6 application for the MPS even though there is a 300lb weight difference and a heavier rear end with the extra lsd and drive shafts in the rear."

I'm really having a difficult time comprehending how a Mazdaspeed6 has more sprung weight than a standard Mazda6. Sounds like a nice little fable to give people a paranoia about the rear end sagging and Eibach being a crappy choice. Eibach is smart enough to realize the car has more weight. Obviously it's in areas that are not 'suspended' and hence, you have their approval!

Let's also logically try to keep in mind that the engine, transmission and drivetrain components are not SPRUNG weight.[/b]

Guess current topic is sprung weight.

Curb Weights 07:
3618 MS6
3320 M6 Mtx Sedan

Engine/trans/diff IS sprung weight, question is what is the extra UNsprung weight? 1/2 of the rear axles, and slightly heavier hubs and brakes. Most of the 300 lb added weight is sprung.

MS6 is listed as 60% front weight bias.

Mazda lists all M6 models at 60% front bias, but, based on car and driver wagon data, I figured only the 6S sedan has 60% front bias. That's why Eibach lists those springs for the MS6.

Any spring but proven coil-overs, or springs from RPM or autoexe, is a real compromise.

Example: MS6 rates are 5.0kg F and 3.7 kg rear. 6S Prokit is 5.8F and 3.6R per Eiback tech line. So you have close to 2" drop with only 16% stiffer fronts, and softer rears.

 

[KevinK2]

Assuming the chassis does not move and you run over a brick, anything that moves up and down with the wheel is UNsprung weight. This includes wheel tire control arms brakes and lower half of the coil spring. All else is sprung weight, ie supported by the springs.