Iron golf club set and golf club head

1. A golf club set comprising n (n is an integer equal to or greater than 2) iron golf clubs,

wherein each of the n clubs has a rail extending backward from an intermediate position in a face-back direction of a sole; and

when a distance d 1 between a leading edge and a rail starting point is defined as d 1 (1), d 1 (2), . . . , d 1 ( n ) in an ascending order of a real loft angle from the club having the smallest real loft angle, the golf club set satisfies the following relation 1:

d 1(1)< d 1(2)≦ . . . ≦ d 1( n ), and d 1(1)< d 1( n )  [relation 1].

2. The golf club set according to claim 1 , wherein the golf club set satisfies the following relation 2:

d 1(1)< d 1(2)< . . . < d 1( n )  [relation 2].

3. The golf club set according to claim 1 , wherein the rail extends to a back face.

4. The golf club set according to claim 1 , wherein

the two rails are provided on a toe side, and a sole groove is formed between the two rails; and

the two rails are provided on a heel side, and a sole groove is formed between the two rails.

5. The golf club set according to claim 4 , wherein

the sole grooves extend backward from the intermediate position in the face-back direction; and

when a distance d 2 between the leading edge and a sole groove starting point is defined as d 2 (1), d 2 (2), . . . , d 2 ( n ) in an ascending order of a real loft angle from the club having the smallest real loft angle, the golf club set satisfies d 2 (1)<d 2 (2)< . . . <d 2 ( n ).

6. The golf club set according to claim 1 , wherein the rail is not brought into contact with a ground in a base state where a face center position Pc is a ground point.

7. The golf club set according to claim 1 , wherein

each of the clubs has the plurality of rails; and

when an average value d 1 a of the distances d 1 is defined as d 1 a (1), d 1 a (2), . . . , d 1 a ( n ) in an ascending order of a real loft angle from the club having the smallest real loft angle, the golf club set satisfies the following relation 3:

d 1 a (1)≦ d 1 a (2)≦ . . . ≦ d 1 a ( n ), and d 1 a (1)< d 1 a ( n )  [relation 3].

8. The golf club set according to claim 7 , wherein the golf club set satisfies the following relation 4:

d 1 a (1)< d 1 a (2)< . . . < d 1 a ( n )  [relation 4].

9. The golf club set according to claim 1 , wherein

each of the clubs has the plurality of rails; and

when a maximum value d 1 b of the distances d 1 is defined as d 1 b (1), d 1 b (2), . . . , d 1 b ( n ) in an ascending order of a real loft angle from the club having the smallest real loft angle, the golf club set satisfies the following relation 5:

d 1 b (1)≦ d 1 b (2)≦ . . . ≦ d 1 b ( n ), and d 1 b (1)< d 1 b ( n )  [relation 5].

10. The golf club set according to claim 9 , wherein the golf club set satisfies the following relation 6:

d 1 b (1)< d 1 b (2)< . . . < d 1 b ( n )  [relation 6].

11. The golf club set according to claim 1 , wherein

each of the clubs has the plurality of rails; and

when a minimum value d 1 c of the distances d 1 is defined as d 1 c (1), d 1 c (2), . . . , d 1 c ( n ) in an ascending order of a real loft angle from the club having the smallest real loft angle, the golf club set satisfies the following relation 7:

d 1 c (1)≦ d 1 c (2)≦ . . . ≦ d 1 c ( n ), and d 1 c (1)< d 1 c ( n )  [relation 7].

12. The golf club set according to claim 11 , wherein the golf club set satisfies the following relation 8:

d 1 c (1)< d 1 c (2)< . . . < d 1 c ( n )  [relation 8].

13. The golf club set according to claim 1 , wherein the golf club set comprises m (m>n) iron golf clubs comprising a club having a real loft angle equal to or less than 42 degrees and having a rail; and a club having a real loft angle greater than 42 degrees and not having a rail.

14. The golf club set according to claim 1 , wherein the golf club set includes a 6-iron;

the head of the 6-iron comprising:

two rails extending backward from an intermediate position in a face-back direction of sole and disposed on a toe side of a face center position Pc; and

two rails extending backward from the intermediate position in the face-back position direction of the sole and disposed on a heel side of the face center position Pc,

wherein the four rails of the 6-iron are not brought into contact with the ground in a base state where the face center position Pc is a ground point.

15. The golf club set according to claim 14 , wherein

a sole groove is disposed between the two rails disposed on the toe side of the 6-iron; and

a sole groove is disposed between the two rails disposed on the heel side of the 6-iron;

wherein the sole grooves of the 6-iron extend backward from the intermediate position in the face-back direction.