Burakkiliboz said:
Hi, I understand that we need spacer and longer bolts. What about tires? Can we use 225/40/18 in front and 255/35/18 in rear with F30 wheels???
To expand on the answer above, which is correct of course, the important number is the rolling circumference or radius.
Tyre sizes are quoted in width (say 225), profile (say 40) and diameter of wheel (say 18"). Why the sizes are both metric and imperial is anyone's guess. The width is in millimetres. The profile is a percentage of the width, in this case 40% (90mm). This will give a rolling circumference of (90mm + 90mm + 457mm x pi) = 2,000mm.
So a different wheel with the same diameter (18" in this case) will need the same tyre dimensions to give the same rolling circumference.
Tyre profiles go up in 5% increments, 30, 35, 40 etc. If you were to increase your diameter of wheel to 19" and put a 40 profile tyre on, it would give a rolling circumference of (90mm + 90mm + 483mm x pi ) = 2,082mm. So 82mm larger. So you reduce your profile by one increment to 35 in this case: 78.75mm + 78.75mm + 483mm x pi = 2,011mm. Only 11mm larger circumference, or 0.5% which is acceptable. I think the 'rule of thumb' is around 1.5% as being OK without problems.
Rolling circumference staying within 'limits' is important to ensure speed is shown correctly and, with modern cars, sensors in and around the wheels operate correctly.
Wheel spacers is a completely different subject....but I'm tired now. HTH
Attleborough, Norfolk
Scottish Borders
