The PCD is the diameter of a circle (usually stated in millimetres) drawn through the centres of all the bolt holes.
The smart fortwo 450, fortwo 451 and Roadster have the same PCD, 3x112.5mm.
The smart Forfour PCD is 4x114.3mm (4.5 inches).
The 453 fortwo and 453 forfour is 4x100mm.
The offset is the distance (in millimetres) from the centre of a wheel cross section.
As it moves away from the car the number increases from zero.
If it moves in towards the car it will go into minus numbers.
This picture is an example of one of the offsets found on the smart, for a full list click
The centre bore is very aptly named, it is the inside diameter of the alloy wheels and the outside diameter
of the bearing that the wheel locates over. The 2 have to match for 2 reasons, firstly it centres the wheel on
the hub so the wheel isn't off centre and therefore vibrate. Secondly it holds the wheel in position so the wheel
bolts only have to hold the wheel to the hub and not take any sheer force from any lateral movement.
Because the forfour was a re-engineered Mitsubishi Colt, it retained the Colt
centre bore which was different to the fortwo and Roadster centre bore.
Fortwo 450 = 57.1mm
Roadster 452 = 57.1mm
Fortwo 451 = 57.1mm
Forfour 454 = 67.1mm
Fortwo 453 = 60mm
Forfour 453 = 60mm