if you can afford it go low profile 205/35 tires...
cheaper option is to remove the plastic arch lining on the insides of every arch with a stanley knife
As it says you DONT need to mod the arches.
You have to have the correct offset tho, which by the sounds of thing you haven't.
I've ran 18s for over a year now. Driven the length of the country with 4 people in the car and a boot full. Not rubbed ever.
I have 215/35/18 and lowered 40mm all round (air bags going on very shortly now, thanks to my boss), yes they rub with people in the back but nothing too major. Not worth rolling the arches though unless you want 19`s.
Air suspension is the way to go.
Don`t roll the arches for 18`s, not worth the expense, just change your tyres IMO.
MK4 Golf 1.8T, Euro Style
i have the same problem with my 17's cos its so low im just going to remove the inner plastic and bond it high up in the arch
Balck Astra K Elite 1.4 Turbo
the tyre profile is wrong and your rolling radius will be out over standard. Lik emost have said you need to change the tryes for 205/35/18's What width are the wheels also? 7J ? Is it running on the inside of the tyre or the outside? Chech the tyre for marks. Front or rear that are rubbing?
I'm running 215/35/18"s but my rims are 7 1/2" wide. Dropped 40mm.
I've got 19's on my car and they don't rub with 5 up!!! I have had the rear arches rolled slightly tho!!