Stud pin and pneumatic tire

A pneumatic tire comprising a tread portion provided with a stud pin installation hole and a stud pin installed in the stud pin installation hole, the stud pin comprising:

• a tip end protruding from the tread portion to make contact with a road surface;
• and
• a buried base including a flanged bottom portion provided on an end opposite the tip end and extending in one direction;
• a flanged trunk portion provided between the bottom portion and the tip end;
• the buried base being embedded in the tread portion of the pneumatic tire in which the stud pin is installed, and pressure from a side surface of the stud pin installation hole on the bottom portion and the trunk portion securing the stud pin;
• the bottom portion including a plurality of first recesses formed on and along an outer peripheral surface thereof that comes into contact with the side surface of the stud pin installation hole;
• the trunk portion including a plurality of second recesses formed on and along an outer peripheral surface thereof that comes into contact with the side surface of the stud pin installation hole;
• and
• the first recesses provided on the bottom portion and the second recesses provided on the trunk portion being provided at a same peripheral position on the outer peripheral surface of the buried base;
• and wherein a first projection is formed between the first recesses on the periphery of the outer peripheral surface of the bottom portion of the buried base, and a shape of the first projection along the bottom portion is a first arc having a radius of curvature of R1 larger than half a maximum size L1 of the bottom portion in a width direction orthogonal to the extending direction of the buried base.