PURPOSE: To make compatible the driving and braking quality with the improvement of the turning performance of an all-season pneumatic tire of a block base pattern having a calf on an iced road by specifying a distribution mean value and a ratio of a maximum value to a minimum value respectively in all directions for a ratio of the total projected length of the calf in a direction orthogonal with an active force direction and a total tread area.

CONSTITUTION: A calf 5 is subjected to an active force F from a direction at an angle of α with a tire peripheral direction E-E'. In this case, the mean distribution value of a ratio ΣLn(α)/S of a total ΣLn(α) to a tread surface area S is set to 0.03 to 0.05mm-1 when the angle α is changed by 0 to 360 degrees for all carves 5 of the projected length (α) in a direction orthogonal with the active force F. Also, a ratio of the minimum value of the distribution to the maximum value is specified to 0.5 or more. According to the aforesaid construction, driving and braking quality is maintained and a cornering performance can be improved on an iced road.