Calculating offset

[TimJM]

I am replacing my wheels/tyres and having just spent a lot of money on a proper geo and setup to get the car right I want to keep as close as possible to the current dimensions to keep the handling right.

I have a Cerbera and I know they are 5x114.3 on 19" rims but I wanted to calculate the width and offsets.

I measured the wheel width and the rear is 11" (so 11J), the front 10" (10J). From the hub to the outside of the wheel is 4" on both back and front.

So my calcs are as follows:

Rear:
11" = 279.4mm. The centre line will be 139.7mm.
From the hub to the outside is 4" = 101.6mm.
139.7 - 101.6 = 38.1mm offset.

Front:
10" = 254mm. The centre line will be 127mm.
From the hub to the outside is 4" = 101.6mm.
127 - 101.6 = 25.4mm offset.

Does this look right before I to order new wheels?

I think people say a Cerbera should run 42mm offset all round or 33 rear and 42 front. Obviously mine are currently different from those but that is probably down to the much wider wheels/tyres I run and the arch work that has been done to give clearance.