Golf ball 2 has a core 4 , a mid layer 6 , a reinforcing layer 8 and a cover 10 . Base polymer of the mid layer 6 includes an ionomer resin as a principal component. The mid layer 6 has a hardness Hm as measured with a Shore D type hardness scale of equal to or greater than 55. Base polymer of the reinforcing layer 8 is a thermosetting resin. Base polymer of the cover 10 includes a thermoplastic polyurethane elastomer as a principal component. The cover 10 has a nominal thickness Tc of equal to or less than 0.6 mm. The cover 10 has a hardness Hc as measured with a Shore D type hardness scale of equal to or less than 54. Ratio (Tr/Tc) of the thickness Tr of the reinforcing layer to the nominal thickness Tc of the cover is 0.005 or greater and 3.0 or less. This golf ball 2 includes dimples 12 having a depth Dp. Thickness Td of the cover 10 immediately below the deepest site of one or more of the dimples 12 is greater than (Tc−Dp).
1. A golf ball which comprises a spherical core, a mid layer positioned outside of the core, a reinforcing layer positioned outside of the mid layer and a cover positioned outside of the reinforcing layer, wherein
the principal component of the base polymer of said mid layer is an ionomer resin,
said mid layer having a hardness Hm as measured with a Shore D type hardness scale of equal to or greater than 55,
the principal component of the base polymer of said cover is a thermoplastic polyurethane elastomer,
said cover having a nominal thickness Tc of equal to or less than 0.6 mm,
said cover having a hardness Hc as measured with a Shore D type hardness scale of equal to or less than 54,
the ratio (Tr/Tc) of the thickness Tr of said reinforcing layer to the nominal thickness Tc of said cover is 0.005 or greater and 3.0 or less,
said goff ball comprising dimples having a depth Dp on the surface thereof, and
the thickness Td of the cover immediately below the deepest site of one or more of the dimples is greater than (Tc−Dp).
2. The golf ball according to claim 1 wherein the proportion P 1 of the number of the dimples on the cover having a thickness Td immediately below the deepest site of the dimple of greater than (Tc−Dp), to the total number of the dimples is equal to or greater than 30%.
3. The golf ball according to claim 2 wherein the proportion P 2 of the number of the dimples on the cover having a thickness Td immediately below the deepest site of the dimple of equal to or greater than (Tc−Dp+0.03), to the total number of the dimples is equal to or greater than 30%.
4. The golf ball according to claim 1 wherein the base polymer of said reinforcing layer is a thermosetting resin.
5. The golf ball according to claim 1 wherein said reinforcing layer has a tensile strength of 150 kgf/cm 2 or greater and 500 kgf/cm 2 or less.
6. The golf ball according to claim 1 wherein said reinforcing layer has a pencil hardness of 4B or greater and 3H or less.
7. The golf ball according to claim 1 wherein both the reinforcing layer and the mid layer are recessed below the dimples.