Summer tires
Do not drive with a tire tread depth of less than 0.12 in/3 mm.
There is an increased danger of hydroplaning if the tire tread depth is less than 0.12 in/3 mm.
Winter tires
Do not drive with a tire tread depth of less than 0.16 in/4 mm.
Below a tread depth of 0.16 in/4 mm, tires are less suitable for winter operation.
Minimum tread depth
Wear indicators are distributed around the tire's circumference and have the legally required minimum height of 0.063 in/1.6 mm.
They are marked on the side of the tire with TWI, Tread Wear Indicator.
BMW X3 Owners Manual > PDC Park Distance Control: Hints
Personal responsibility
Even an active system does not relieve
the driver from personal responsibility while
driving.
Technically the system has its limits, it cannot
independently react to all traffic situations.
Monitor your driving, be on the alert, observe
the vehicle surroundings and ...