Thinking of getting after market rims, the main reason is to improve the looks but I would like a improved grip level and have high cornering speeds. Which would be best 17's or 18's.The 16's are just to small!
I don't want to make the ride on normal roads bad , but i could stand it a little worse.

Any advice from abybody whose recently changed up to bigger wheel would be great

 

17x7.5 & 17x9 would be my pick.

Tire rack has some ASA's for a good price with those specs
Volk has ce28n's with those measurements also.

Then I would run a sticky 225/45/17 and 255/40/17 tire.
For 255's in rear...you will need at least +60mm offset for the 17x9's in rear.
The ASA and CE28n's have offsets in excess of +60mm.

 

I don't know what that figg'in title is about

 

Do as Unicorn suggests and you will be fine. Many of the wheels, that some are running on the S, require tires that are narrower than the SO2's and don't offer the grip.

My first requirement for getting new wheels was to increase tire width. I accomplished that by going with the ASA's 225/255 setup. I love the tire widths (no rubbing and my car is lowered) and I did not have to take a second on the house to buy them.