245/40/18 is just to big.. it slows the car down because of the greater circle one turn takes...

and the car cant be lowered enough to it looks like a off road car..

245/30/18 would result in a close to the standard size , so my speedometer would be correct aswell ..

other choice would be 235/35/18 resulting in the same size as the standard wheels of a cosworth...
but 245 looks more bling but cant find any on the net..