I strongly suggest you do not lower a European Specification 328 without first calculating the position you will need for the bump stops that are internal with the dampers. So, do the bump stops, maybe increase the compression and re-bound a little for the dampers and increase the spring rate probbaly about 20% as a guess. At full compression, the 328 will scrape the chassis rails just forward of the front suspension pick up points anyway so be warned. Added to that, the car will pick up bump steer from the offset tie rod ends (Unless you lower the rack with the car). Good luck with your project, if you do it properly, you have a lot of development to do.
Well, hold on here. While I'm in agreement that you shouldnt lower a Euro model (or any other car for that matter) without checking the very complete list carl888 gave you, you might need to! You haven't given us the size of your new rims. You'll need to calculate the new over all radius of your wheel and tire combo to see if you'll be raising the car from its current ride height. For example: let's say you're currently running 225/45/16 (I just pulled that out my butt) the radius is (225*45%=101.25mm. which is 3.99 inches) so, 3.99"+7.5"(radius of wheel) gives you a wheel/tire height of 11.49" to the center of your wheel hub. If you go to say 225/35/18 the radius is (225*35%=78.75mm which is 3.1 inches) so, 3.1"+9"=12.1" wheel/tire height there by raising the car an additional (12.1"-11.49"=) .61" Your car would now be sitting an addtional 1/2" higher. You'll need to drop it back down that 1/2" to get any advantage of the new wheel/tire combo. Otherwise I'd say rising your center of gravity that extra bit is a step backwards in regards to improving cornering performance. But, even if you do so you'll need to go through the list above.
He he, well done Kurt, thanks for the correction, no excuse for incorrect information except a bottle of wine!
