I suspect it is because, if used, there will be unmatched wheels on the vehicle so the 50mph maximum speed is probably enshrined in some law somewhere for the use in emergency only.
Because the wheel will be a different width and weight to the alloy on the other side if it is on the front there is a potential for a braking and steering inconstancy. Less so on the rear but the vehicle manufacture could be liable in the event of a incident of lost control if they did not insist on a low limit.
26-04-2021, 01:53 PM (This post was last modified: 26-04-2021, 01:53 PM by Pedronicus.)
The number of BMWs that I see flying along the M25 well over the limit and one wheel is a spacesaver is beyond belief. Local plod nicked one recently doing 110mph.