Under National Standard GB 7258-2017 (Technical Specifications for Safety of Motor Vehicles in Operation), what is the minimum statutory tire tread depth for ordinary motorcycles?

1. Not less than 0.5 mm
2. Not less than 3.0 mm
3. Not less than 1.6 mm (不得小于1.6毫米，或磨损至磨耗标志)
4. Tires have no minimum depth standard as long as fabric cords are not showing