Wheel width is determined by required tire size, required handling target performance and package space on the vehicle. The design of the wheel is led by styling, but JLR aim to match the weight and stiffness across all styles so the vehicles have a consistent performance regardless of the visual aspect of the wheel.
The offset of the wheel affects the steering and handling of the car, so JLR ensure that there are only small differences in offset across the different wheels styles, again so the vehicle performance is consistent.
The wheel design also has to be sufficiently strong and robust to carry the front and rear axle loads of a car loaded to GVW condition. The wheel paint finish has to meet a stringent corrosion resistance specification. A stringent test programme is conducted on each wheel to validate its strength and resistance to corrosion.
JLR test requirements for strength and fatigue are significantly more stringent than the industry minimum SAE test procedure. Non OE Wheels may not necessarily have been designed and tested with the relevant vehicle load conditions in mind.
Non-OE wheels may not have the same high standards of corrosion protection, and hence show cosmetic defects much earlier. It is likely that the non-OE production process will be generic, and hence the wheels will be less uniform (round) which potentially could cause vehicle vibration concerns.
Non-OE wheels will be designed to fit a variety of vehicles, and so will not be specifically optimized for the Jaguar product in terms of rim width or offset. Using wheels of an incorrect geometry will result in potentially higher wear in suspension bushes and hub bearings and change the handling/steering behaviour of the car.