whats the correct tyre presure for 18"

 

For 235x40x18 Prodrive recommend 35psi for the fronts and 31psi for the rears on the sheet that comes with the spring kit.

 

Same as for 17" or any other size. Tyre pressures are relative to the weight of the vehicle, not the size of the wheel or tyre.

 

Used to set my 18s" at 35/33 f/r as recommended by Mike Wood - lightened steering but you could feel every pebble and wore the track centres away for being slightly over-inflated.

Car came back from dealer service one time and ride was a lot better - asked them what they'd done and they said to set the pressures to those on the b-pillar, i.e. standard pressures of 33/32. This is for an MY05 STi.

 

i use 32 in the front and 35 in the rear on mine

 

37/35