[auscobra]

Anyone know the proper way to calculate wheel offset before I order any wheels?
I have the tyre widths, distance between where I want the outside of tyres to be, and distance between hub faces. Body is not on the car.
I assume the calcualtion would be
(tyre width / 2) - ((distance between outside of tyres - hub to hub distance)/2)

In the case for my rear wheels it would be (this is approx)
(315 / 2) - ((1680-1400)/2) = 17.5mm offset.

This in effect is the distance between where the wheel/tyre centre would be to where the hub face is.
Tyres haven't arrived yet so I will be meauring these once I get them. I would guess 315's may be slightly different when actually measured. Is this the case?

Have I got this calcualtion right?

Cheers,
Auscobra