The car has an approval for the complete vehicle with certain combinations of wheel rims and tyres.
All wheel rims have a dimension designation, for example: 8Jx18x42.5.
8  | Rim width in inches | 
| J | Rim flange profile | 
18  | Rim diameter in inches | 
42.5  | Off-set in mm (distance from wheel centre to wheel contact surface against the hub) |