Okay so the Mk4 GTI has the standard 16" wheels. I believe the tyre dimensions to be 205/55R16.
I want to get 17" wheels with a 205/8" width and stretch the tyres. I would put a 195 width tyre on but to keep the outer diameter the same so that the speedo doesn't read the wrong speed, what sidewall dimension would I need to get. Isn't true that if you stretch a tyre then the sidewall size becomes smaller because your basically pulling the tyre closer to the wheel?
I would also like to know the sidewall size I would need for 17 inch rims if I was just to fit the a normal 205 tyre onto the 8 inch wide rims and keep the outer diameter of the tyre the same as the standard 205/55R16 tyres.