I have a 2018 S3, i have just upgraded to 50mm Carbons (25mm external) with GP5k’s i have got a huge amount of rub on the inside of my chain stays, its gone through into the carbon. i tried running 23mm tyres and still the same, i think it is down to the width of the wheel and not enough clearance. i say that, but i am a big guy. im at a loss as to what to do as 90% of wheels now are atleast 25mm wide.