Just wondering that how big tires can u fit on S4 stock FC ?
Considering the suspension and all are stock...

I have 225/45 R17 on the rear... 215/40 R17 on the front...
Can I put 225/45 on the front too without rubbing problems ?

 

Well yes you can run 225/45/17 in the front, hell there are some guys who are running 245 up front, its just all in the offset/size/ of your rims and your roll/pull/oversize of your fenders thats all. So here have fun and start reading the great FC wheel fitment guide. The Official FC Wheel Fitment Thread

 

It would depend on the section width of the tire and your well offset. It would be the same width as a 225/50-16, but not all manufacturer's have identical sizes, some would fit on the stock wheels and no rubbing, others wouldn't.
Why not put your rear tires on the front and give it a try.

A quick check shows that the section width on the 224/45-17 runs from 8.7" to 9.4". That .7 of an inch makes a big difference when it's close.

 

Thanks
This makes things so much easyer, maby I´ll change the rear tires to the front tomorrow and give it a shot...