Some reading to pass the time>
Tyre size options on 18", and other wheel sizes, but 18" especially are governed by the weight of the Cali which requires a minimum of a 101 load rating.
Load rating increases by 25kgs per digit, ie 101=825kgs, 102=850kgs, 103=875 kgs etc. Multiply that figure by 2 for the axle load capacity and again by 2 for total vehicle weight capacity. You should always have a safety margin to allow for weight transfer when cornering or braking not to mention potholes and kerb mounting.
You can go up in load rating legally but not down. Commercial VW van may have up to 117 load rated tyre fitted.
The Sportline rim will be probably be 8" wide. VW dealers supplied these with 235/50/18 101 tyres, probably because that is a cheaper tyre than a 255/45/18 103.
235/50 and 255/45 give very similar circumference to a 235/55/17 tyre. The 255/45 has slightly less resulting in road speed being less than indicated. The 50 and 45 figures are the sidewall height/profile as a percentage of the width. As the tyre width increases the profile must reduce to keep the circumference equal.
A 255 being wider will give better rim protection than a 235 against kerbing.
The 235/55/18 104 size is mainly made for the SUV market and is in my view a suitable alternative as SUV tyres have stronger sidewalls and the tread design copes with mud and stone clearing out better than normal road only designed treads. They also have a bigger range of Manufacturers and tread designs than the 255/45/18 103 tyre. Cheaper as well plus the actual road speed and indicated speed are pretty close.
VW Factory sized tyres usually have 2 or more MPH error at 70MPH. Indicated 70 but only about 68MPH road speed. Good for a camera safety margin, 235/55 has no safety margin other than not going over indicated speed.
I also like the increased sidewall for dealing with our potholed roads.
Tyres are a personal choice ultimately.
One to consider is the Pirelli Seal Inside as it is a bit of insurance if no matching spare carried.
Incidentally I have an 18" rim with a 235/55/18 tyre fitted that fits in the spare rack. Was a trial but stuck to 17" wheels in the end.
Pirelli Cinturato All Season Plus 235/55 R18 104V XL, Seal Inside Buy online, free shipping for orders of 2 or more tyres and quick deliveries from mytyres.co.uk - order comfortably online now!
www.mytyres.co.uk