Firstly, I'm NOT an expert and would never claim to be. A lot of my knowledge has been gained from this forum and from people that know what they're talking about like docwra. I refer to your quote below:
OK, here's what I think has happened, as, under your own admission, you know nothing about cars and performance.
You asked the above question as you noticed the size of the tyres fitted to your car and were then told what the standard sized tyres were. You then purchased a set of standard sized tyres.
One importand factor missing is that you don't appear to of mentioned that you're running non standard wheels, that aren't the same size as the OEM ones. I think it may even be luck that you're current wheels are 18's - otherwise you'd of had even more problems!
Sorry if this comes across as being a bit blunt, it's not my intention. I just hope this helps answer why your tyres don't look quite right