These are 16" wheels...... how are you fitting 18" tyres to them exactly ?
What you're asking is a bit difficult to answer, technically speaking with 185/50/16 tires I don't think you're too far off what the original wheel fitment is. Really you should be matching the tires dimensions to what ever the original fitment is so that you keep the accuracy of the speedometer but if you start lowering it even with the OEM wheels there will come a point the wheel will rub.
So how much you lower the car, how much weight is in the car the tires and wheels all have a bearing. If you are not sure then you should be speaking to specialist about what you can and can't do. Chances are if you start lowering the car massively then you'll always have issues with rubbing.
Then there is the width, a quick search shows a 8 inch wheel should have a minimum 215mm width of tire fitted, 225 -235 is the ideal spot. I get that people like the stretched tire look but the more you push it the more dangerous the tires become and I think you're seriously overdoing things with a 185 tire on an 8 inch wheel.
^^^^^^ this, all of this. I think you're taking your life in your hands with this and your insurance company wouldn't touch you.