Nope, suspension cannot be adjusted. Pretty much all X3s have a "firm" ride, its just simply a matter of how firm it is. A 2004 or a sport model will have a much harder ride than later years without the sport suspension. However in order to get the X3 to handle as well as it does, the engineers pretty much designed the suspension settings to be on the aggressive side.

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2014 Mazda 3 GT: Ø Consumption: (click for details)