The depth of the grooves in a tire (pneumatic-air pressure) which comes in contact with the road should not be less than:

Why this is the answer

The correct answer in the official bank: 2mm, including the spare tire.

The tread grooves of a tire that touches the road must be at least 2mm deep, and this applies to the spare tire too, since it may be fitted at any moment and used for driving. Shallow grooves clear less water, so grip on wet roads drops and braking distance grows. 2cm is far deeper than the tread of any ordinary tire.

Topic: Rules and regulations. The bank marks it for these classes: Light truck (C1), Heavy truck (C), Bus (D), Motorcycle (A), Private car (B).