A quick search of 18” brought up this:
Providing the rolling radius is the same, your speedo reading should change.
Website www.willtheyfit.com will confirm this.
Click on the “18"” tag at the bottom to read a bit more about 18’s, such as wheel spacers etc
Two tyre sizes for 18” recognised by VW;
235/50/18 for up to T30
255/45/18 for T32
For standard summer tyres we tend to fit the bigger tyre to all applications, to offer more wheel protection.
Providing the rolling radius is the same, your speedo reading should change.
Website www.willtheyfit.com will confirm this.
Click on the “18"” tag at the bottom to read a bit more about 18’s, such as wheel spacers etc