A golf ball 2 has a large number of dimples 8 on a surface thereof. A trajectory of the golf ball 2 is divided into first to fourth segments. An average CD 1 of drag coefficients CD and an average CL 1 of lift coefficients CL in the first segment are equal to or less than 0.225 and 0.180, respectively. An average CD 2 of drag coefficients CD and an average CL 2 of lift coefficients CL in the second segment are equal to or less than 0.250 and 0.220, respectively. An average CD 3 of drag coefficients CD and an average CL 3 of lift coefficients CL in the third segment are equal to or greater than 0.260 and 0.220, respectively. An average CD 4 of drag coefficients CD and an average CL 4 of lift coefficients CL in the fourth segment are equal to or greater than 0.250 and 0.200, respectively.
1. A golf ball having a large number of dimples on a surface thereof, wherein
when a trajectory that is calculated under conditions of a ball initial speed of 57.4 m/s, a launch angle of 13.8°, and an initial backspin rate of 2450 rpm by a program created according to a manual provided by the USGA using a drag coefficient CD and a lift coefficient CL obtained through an ITR, is divided into a first segment from a launch point to a midpoint between the launch point and a top, a second segment from the midpoint between the launch point and the top to the top, a third segment from the top to a midpoint between the top and a landing point, and a fourth segment from the midpoint between the top and the landing point to the landing point,
an average CD 1 of drag coefficients CD in the first segment is equal to or less than 0.225,
an average CL 1 of lift coefficients CL in the first segment is equal to or less than 0.180,
an average CD 2 of drag coefficients CD in the second segment is equal to or less than 0.250,
an average CL 2 of lift coefficients CL in the second segment is equal to or less than 0.220,
an average CD 3 of drag coefficients CD in the third segment is equal to or greater than 0.260,
an average CL 3 of lift coefficients CL in the third segment is equal to or greater than 0.220,
an average CD 4 of drag coefficients CD in the fourth segment is equal to or greater than 0.250, and
an average CL 4 of lift coefficients CL in the fourth segment is equal to or greater than 0.200,
each dimple has a contour shape that is non-circular, and
the golf ball satisfies the following mathematical formula:
( Rh max− Rh min)>( R 1 −R 2),
wherein, in the mathematical formula, Rhmax represents a radius variation range of a dimple having a maximum radius variation range Rh, Rhmin represents a radius variation range of a dimple having a minimum radius variation range Rh, R 1 represents an average radius of the dimple having a maximum radius variation range Rh, and R 2 represents an average radius of the dimple having a minimum radius variation range Rh.
2. The golf ball according to claim 1 , wherein each dimple is obtained based on a contour of a Voronoi region assumed on a surface of a phantom sphere of the golf ball.
3. The golf ball according to claim 2 , wherein a pattern of the dimples is obtained by a designing process comprising the steps of:
(1) assuming a large number of circles on the surface of the phantom sphere;
(2) assuming a large number of generating points based on positions of the large number of circles;
(3) assuming a large number of Voronoi regions on the surface of the phantom sphere by a Voronoi tessellation based on the large number of generating points; and
(4) assigning a dimple and a land to the surface of the phantom sphere based on contours of the large number of Voronoi regions.
4. The golf ball according to claim 1 , wherein a radius variation range Rh of each dimple is equal to or greater than 0.4 mm.
5. The golf ball according to claim 1 , wherein each dimple meets the following mathematical formula:
Rh/Rave ≧0.25,
wherein, in the mathematical formula, Rh represents a radius variation range, and Rave represents an average radius.
6. The golf ball according to claim 1 , wherein a difference between a radius variation range Rhmax of a dimple having a maximum radius variation range Rh and a radius variation range Rhmin of a dimple having a minimum radius variation range Rh is equal to or greater than 0.1 mm.