Hi guys I'm looking for some help. My local dealership (100 mile round trip) were less than helpful so im hoping some of you friendly people can help!

I have owed my GTC for almost a year on a 63 plate. It has lots of extras including the upgraded body kit and 19" alloys. However since owning the car I have noticed the rear suspension is very soft. When I brought the car from the main dealer it had 4 new tyres fitted 235/50/R19's the first weekend I had the car me and my fiancée went away and whilst away every bump in the road was causing the tyres to rub the inner arch lip! After contacting Vauxhall I found out the profile of the tyre they had fitted was incorrect and should have been 235/45/R19. As a matter of course they replaced the tyres but to be on the safe side I had them fit 235/40/R19's after having confirmed it should not impact the speedo by the dealership. However I still fine the back end soft and it rubs the arches. I have had the springs etc looked at and they all seem fine. The car also has low mileage and is more a weekend toy. Before I upgrade the springs to stiffer aftermarket springs has anyone else had this problem and what did they do about it?

I have been recommended eibach lowering springs for the car as they have a higher load rating as well as improving the look filling the arches more. Has anyone used these and to what success?

Thanks in advance people!