Iron type golf club head

An iron-type golf club head comprising:

• a heel portion;
• a toe portion;
• a sole portion;
• a top-line portion having a total top-line thickness of no greater than 9 mm;
• and
• a striking face having a flat forward-facing ball-striking surface having a loft of 18-64 degrees, a face center, and a rearward-facing surface;
• wherein the striking face has an unsupported region with an unsupported striking face thickness that varies, a heel portion of the unsupported region is located on a heel side of an imaginary center vertical plane that extends perpendicularly to a ground plane and that contains an imaginary line that extends in a direction normal to the striking face at an ideal striking location when the club head is in a normal address position, and wherein a toe portion of the unsupported region is located on a toe side of the imaginary center vertical plane;
• wherein a face stiffness ratio of a mean point-wise cross sectional bending stiffness of the toe portion of the unsupported region to a mean point-wise cross sectional bending stiffness of the heel portion of the unsupported region, is at least 1.20;
• wherein a vertical wall hitting region of the unsupported region of the striking face lies between an imaginary heel side vertical plane and an imaginary toe side vertical plane, where the heel side vertical plane is spaced 20 mm to the heel side and is parallel to the center vertical plane, and the toe side vertical plane is spaced 20 mm to the toe side and is parallel to the center vertical plane, and the following inequality is satisfied:
• [
• (
• ∑
• n
• =
• 1
• N
• E
• n
• ⁢
• t
• n
• 3
• )
• ÷
• N
• ]
• ÷
• [
• (
• ∑
• m
• =
• 1
• M
• E
• m
• ⁢
• t
• m
• 3
• )
• ÷
• M
• ]
• >
• D
• v
• ⁢
• w
• ;
• wherein:
• DVW is 1.25,
• En and tn are the effective Young's Modulus value and the unsupported striking face thickness, respectively, for an nth cross-section of the toe portion of the vertical wall hitting region of the striking face,
• Em and tm are the effective Young's Modulus value and the unsupported striking face thickness, respectively, for an mth cross-section of the heel portion of the vertical wall hitting region of the striking face, and
• N and M have values determined by discretizing a SATOE HR and a SAHEEL HR within the vertical wall hitting region of the striking face, respectively, into 1 mm×1 mm sections;
• and
• wherein the club head has a relative coefficient of restitution that is in a range from −0.045 to 0.000.