Whilst this is a useful little on-line wheel calculation tool, it suggests that it is perfectly alright to go changing the offset as long as you can fit the wheel within the body or it won't stick out too far. The whole purpose of the wheel offset it to keep the centre line of the wheel aligned with the centre line of the wheel bearings in the hub. If you change the offset, you put a torque loading on the bearings which they were not designed for, and they will wear and fail prematurely.
The calculator is quite useful as it shows the displacement of the centre line as you alter the offset.
The aim when fitting different wheels is to keep the offset the same or very close to the original to minimise the twist effect on the bearings. On a car with easily replaceable wheel bearings, I suppose it would not matter quite as much since they could be replaced regularly; but on a Bagheera or Murena where they are a big job to replace you really should not be changing the offset.
Roy
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