Tyre pressures on upgraded alloys

[T6180]

Ok ....so there are many threads regarding what size wheels and tyres to fit but I haven't found one regarding tyre pressures with upgraded wheels.

I intend to fit 8.5jx20 fronts with 255/45/20 tyres and 9.5jx20 rears with 275/40/20 tyres.....is there a thread anywhere that covers this off?

I've heard of wetting the floor and rolling over it to see if the tyre leaves the correct tread pattern on the floor...but this seems a bit of a crude method

 

[Steve1978]

I run my 18s at 42 psi. I played around between 32 and 45 until it felt right. Like you say, crude!