The fronts for my work S1 are 18x7 +37.

I got a BBK wheel offset in the front. The previous owner put a 215/35/18 tire on the wheel. Can I up the tire to 40 series. With rolled fenders and lowered, would I have a problem? I just feel a 35 series seem too skinny for an 18in tire up front.

 

yes, you could go with a 40 profile 215

...well, you should.

 

Does that mean that I should not rub with fenders rolled and my car is not dropped aggressively? I haven't driven them on the car yet but isn't 35 series not made for an 18" front wheel?

 

it depends on how wide the tire is...

if you run a 215 or 225, you'll want a 40 profile
it you run a 245, 255, 265, 275 you'll probably want a 35
if you start to run 285+ 30 profile

no, if you roll your fenders, or run some camber, you should be just fine.