What is the minimum legal tread depth for a bus tyre in Ireland?

1. 2.0 mm across any visible part of the tread on a steering axle
2. 3.0 mm across the central half of the tread on all driven wheels
3. 1.0 mm across the full width of every tyre fitted to the bus
4. 1.6 mm across the central three-quarters of the tread around the tyre