What do you think, could i fit my st wit 17" rims and 225/40 or 215/40 wheels?
Would i need some spacers?

The rims on the ST should already 17" if you live in the UK. If you are talking about using the standard rims you will not be able to fit 225. You might get away with 215's though. In both cases however if you keep the 40% profile you will change the overall diameter of your wheel (standard being 40% of 205) resulting in lower performance.

so i should go with 215/35 or 205/40

Yes either of the 2 should work. The difference in radius between those two should be only 7 mm and the 215's are the lower diameter which means it will pull slightly shorter. IMO you should stick with the 205/40's though as that is the standard dimension. For the 215's you should also investigate if they are tolerated for the width of the rim and that is a different story altogether. I think the width of the ST wheels is 7 inch thouch I have 16's so I don't know for sure for the 17's. Before you buy a tyre go to the tyre manufacturer website and they will tell you the tolerated rim width for a particular tyre. I know for instance that TOYO do - I've been looking at track day tires from them and they 'don't make a tyre for my 16 inch wheels, but they do make a good 205/40x17 which is why I'm now hunting for a set of 17's. Hope this helps you.

I recall seeing pictures on a forum of a performance blue ST with 18x8 FRS wheels and then with 19x8 OZ Superleggeras but I can't seem to find it now. It would have been an interesting thread to read. I think he found the Superleggeras were too big and the FRS wheels were OK but he was going to try 18x7 ST220 wheels.

Would 17x7,5 fit the

Hi Danku,
Depends on the tires that you will fit on them and on their offset.