Alloys for XC70

[MartinK]

Originally Posted by fwoody

Hi JonnyA, Does going down a rim size from 17" to 16" or I suppose going up from 17" to 18" not effect your speedometer reading?

fwoody - you would need a tyre with a different depth of sidewall. If tyou have 17" now, and go to an 16" rim, you would need a tyre with more sidewall to retain the same rolling diameter for the wheel. If you went from 17" to 20 inch, you would need a lower profile tyre, to maintain the same rolling diameter of the wheel as a whole - this keeps your speedo (and the car's gearing) correct. See this (borrowed) table:



The tyre shop (or faff with google for a while) will show you which tyres you need. However I stayed with 17" on summer & winter wheels to keep the car standard.

When you are looking at tyre sizes (see table above), the first number (eg 255) is the width in mm, the second number is the "aspect ratio", and the final number is the rim width (in inches bizarrely). Teh letter "R" is the speed-rating for the tyre (R is slow...V and H are what we would need)


The aspect ratio is a bigger number for more depth of sidewall, and a smaller number for a lower profile tyre.