i don't know if i'm going crazy or what, but i always thought the stock A4 wheels were a +35mm offset...then when i got my S4 wheels with the 45mm offset, they stuck out further, which would make sense if the stock wheels were a 35...but i just found out that my old stock wheels are stamped with a 45mm offset too....wtf?!

 

Actually the opposite is true - a larger positive offset will move the wheel/tire further inwards towards the car. See this offset calculator for details.

 

If you have wheels with same offset, but one set is thicker, wouldn't they stick out more? Probably not directly related to thickness and offset, but thickness would affect both inner clearance and outter protrusion...

 

If you mean one is wider, then yes - given the same offset it will stick out further on both the inside and the outside an equal amount.

 

^^^ right!