A base polymer of a cover 3 of a golf ball 1 includes a thermoplastic polyurethane elastomer as a principal component. Dimples 6 are formed on the surface of the cover 3. A proportion R 1 of number of dimples 6 having a ratio (B/T), which is a ratio of a height B of a bottom of the dimple 6 to a nominal thickness T of the cover 3, of equal to or less than 0.70 occupied in total number of the dimples is equal to or greater than 10%. A proportion R 2 of number of dimples 6 having the ratio (B/T) of less than 0.30 occupied in total number of the dimples is equal to or less than 10%. A mean value of the ratio (B/T) for all the dimples 6 is equal to or less than 0.86. The golf ball 1 includes a mid layer 5 having Shore D hardness of equal to or greater than 55. Difference (Hm−Hc) between Shore D hardness Hm of the mid layer 5 and Shore D hardness Hc of the cover 3 is equal to or greater than 5.
1. A golf ball which comprises a core, a cover and numerous dimples formed on the surface of said cover,
wherein a base polymer of said cover includes a thermoplastic polyurethane elastomer as a principal component, and
a proportion R 1 of number of dimples having a ratio (B/T), which is a ratio of a height B of a bottom of the dimple to a nominal thickness T of the cover, of equal to or less than 0.70 occupied in total number of the dimples is equal to or greater than 10%, and
wherein a proportion R 2 of number of dimples having said ratio (BIT) of less than 0.30 occupied in total number of the dimples is equal to or less than 10%.
2. The golf ball according to claim 1 wherein a mean value of the ratio (B/T) for all the dimples is equal to or less than 0.86.
3. The golf ball according to claim 1 , further comprising a mid layer having a Shore D hardness equal to or greater than 55.
4. A golf ball which comprises a core, a cover and numerous dimples formed on the surface of said cover,
wherein a base polymer of said cover includes a thermoplastic polyurethane elastomer as a principal component, and
a proportion R 1 of number of dimples having a ratio (B/T), which is a ratio of a height B of a bottom of the dimple to a nominal thickness T of the cover, of equal to or less than 0.70 occupied in total number of the dimples is equal to or greater than 10%,
wherein said core has a center and a mid layer, and wherein the Shore D hardness of the mid layer is greater than the Shore D hardness of the cover, and
wherein a proportion R 2 of number of dimples having said ratio (BIT) of less than 0.30 occupied in total number of the dimples is equal to or less than 10%.
5. The golf ball according to claim 4 , wherein a mean value of the ratio (B/T) for all the dimples is equal to or less than 0.86.
6. The golf ball according to claim 4 , further comprising a mid layer, wherein the difference in the Shore D hardness of the mid layer and the Shore D hardness of the cover is equal to or greater than 5.
7. The golf ball according to claim 6 , wherein Shore D hardness of said mid layer is equal to or greater than 55.