Speed restrictors are often set to the maximum tyre speed minus a bit of margin. eg. a "W" rated tyre is 270kmh max rated, so the manufacture might set the max

Speed restrictors are often set to the maximum tyre speed minus a bit of margin. eg. a "W" rated tyre is 270kmh max rated, so the manufacture might set the max vehicle speed to 250. Tyres get exponentially more expensive as speed ratings go up.