What is a wheels offset
A wheels offset is the distance from the centre line of the alloy wheels to its mounting face of the hub.
Alloy wheels offset are normally stamped into the alloy wheel and are measured in mm. On the alloy wheel you should see ET and then a number, for example ET38, this is your offset in mm.
A wheel with a zero offset would have its mounting face in line with the centre of the wheel.
A wheel with a negative offset would have its mounting face towards the back of the wheel, this is common on rear wheel drive cars.
A wheel with a positive offset would have its mounting face towards the front of the wheel, this is more common on small front wheel drive cars.