rolling radius help!

[CJA318T]

finally ready to upgrade and looking at a set of 18's tonight. Someone mentioned i should check the rolling radius so that it doesn't screw my speedo up!

old tyres are 205/55/16's
new are 225/40/18's

will the new 18's be ok? help please!

cheers

2001 A3 1.8T Sport

 

[S3-ROB]

Try this site mate

TYRE_SIZE_CALCULATOR

 

[Dave_Bayern]

Yes, its within normal tolerances so not enough for you to actually have to take any notice of on the speedo.

The rolling Radius issue only tends to be a problem when fitting the likes of 18" wheels on Saxos and things, basically actually increasing the rolling radius they were designed for as the Saxo has a small standard wheel.

The middle figure in your 225/40/18 is actually a percentage of the first figure, not a fixed sum in itself, as its the percentage of sidewall compared to width.

Basically, yes it'll be fine and the speedo wont really change.