I believe the 4.8 suspension is stiffer. Probably different shocks and springs. I think the sway bars are the same though. The 20" wheels add to the stiffness in the 4.8 as well. One way to confirm if the suspension parts are different would be to compare part numbers on realoem...

Curious - why do you ask?

EDIT: Oops - I though you were comparing the 4.8 to the 4.4! My eyes are getting older... Anyhow, obviously take the wheels out of the equation, but realoem may still be helpful. However, since you're talking about a 4.6, even if the part numbers are different, it doesn't mean the 4.8 is stiffer. Sorry for the non-help...

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'08 335i Coupe - Barbera Red / Saddle Leather / Light Poplar Wood / 6spd Manual
Options: Sport, Premium, Cold Weather, Comfort Access, Active Steering (awesome!), Power Rear Shade, IPod Adapter, Navigation w/IDrive
Mods: M6 Wheels, Split Armrest, M-Steering Wheel, Euro Light Switch w/Rear Fog Lights, Short Shift Knob w/Matching E-Brake Handle, Clear Reflectors, CDV, Clear Bra

Retired:'04 X5 4.4i