Why must agricultural tractor tyre pressures be adjusted when transitioning from soft field work to high-speed road transport?

1. Field pressures give too little grip on asphalt, so the wheels spin under power
2. Field pressures raise the rolling resistance so much that the engine overheats
3. Low field pressures let the sidewalls flex excessively, which overheats the tyre, spoils directional stability and wears the tread rapidly at road speed
4. Field pressures raise the tractor's design speed above its rating