yes correct ALL BELOW IS A GUIDE ONLY FOR EXAMPLES OK hope it helps all
If you need info p.m me ok happy To help when i can Tyres i love them
if you calculate rolling radius to tyre size using the usual formula will be 99.9% same if calculated with accuracy
So if you add 1 inch to diam of wheel eg 17 to 18inch add 20mm to tyre width and reduce/subtract aspect ratio by 10%
This gives you the calculated rolling radius for accurate readings on speedo and mileage
there is a formula for calculations
EG running 245-45-17 17inch x 9.5 wheels changing to 18inch wheels based on same width
wheel radius is half diam (17)so 8.5inch/215.9mm + side wall 45% in mm is 110.25mm
rolling rad is 215.9mm +110.25mm = 326.15mm
so 18inch x 9.5 wheel for example
245mm width as 9.5 inch wide (tyre is 245mmwide to start as 9inch rim)
radius is 9.5inch/241.3mm half diam
so to calculate we need a rolling radius of 326.15mm
so aspect ratio must be a % of 325.15mm we need for rolling radius - half wheel diam 241.3mm
so rolling required is 325.15mm - 241.3mm half wheel diam = 83.85mm
Calculate aspect ration from mm to % of 245 mm wide tyre which is done by
245mm tyre width calculate what % 83.85mm is of the tyre width which is (34.10%) = 35/40% aspect ratio
so all in the tyre can be 245-40-18 or 245-35-18 if wheel is wider this is based on 9.5inch/241.3mm wheel change figures for wider wheels on the above formula(or ask)
This should keep speedo and mileage accuratly in range for the change
:hohoho: ok
merry xmaS