Method of selecting a golf club shaft

Abstract

An optimal golf club shaft for a golfer is selected from among various golf club shafts, the following. At first, a head speed of a golf club at a point when the golf club strikes a golf ball during a golf swing and a downswing time amount from a top point in time when a downswing begins during the golf swing until a golf ball striking point in time are detected. Then a golf club shaft stiffness suited to the golf swing by using the head speed at the time the golf ball is struck and the downswing time amount is computed. Finally, a golf club shaft having the computed golf club shaft stiffness is selected. The golf club shaft stiffness is computed such that the optimal golf club shaft becomes stiffer as the head speed becomes higher and/or as the downswing time amount becomes longer.

1 . A method of selecting a golf club shaft, comprising: 
 detecting a head speed of a golf club at a point when the golf club strikes a golf ball during a golf swing, and detecting a downswing time amount from a top point in time when a downswing begins during the golf swing until a golf ball striking point in time;    computing a golf club shaft stiffness suited to the golf swing by using the head speed at the time the golf ball is struck and the downswing time amount; and    selecting a golf club shaft having the computed golf club shaft stiffness.    
   
   
       2 . The method of selecting a golf club shaft according to  claim 1 , wherein said computing of a golf club shaft stiffness includes computing the golf club shaft stiffness to be larger as the head speed is higher and/or as the downswing time amount is longer.  
   
   
       3 . The method of selecting a golf club shaft according to  claim 1 , wherein: 
 a vibration frequency of the golf shaft is taken as an indicator of the golf club shaft stiffness; and    said computing of a golf club shaft stiffness includes computing the vibration frequency of the golf shaft based on the following equation:      vibration frequency( cpm )= a   0 + a   1 × HS ( m/s )+ a   2 × T (second)  (1)    where symbol HS denotes the head speed, symbol T denotes the downswing time amount, and symbols a 0 , a 1 , and a 2  denote constants.    
   
   
       4 . The method of selecting a golf club shaft according to  claim 3 , wherein: 
 the constant a 0  is within a numerical range of 21±5;    the constant a 1  is within a numerical range of 4.3±1; and    a 2  is within a numerical range of 157±40.    
   
   
       5 . The method of selecting a golf club shaft according to  claim 1 , wherein: 
 a vibration frequency of the golf shaft is taken as an indicator of the golf club shaft stiffness; and    said computing of a golf club shaft stiffness includes computing the vibration frequency of the golf shaft based on the following equation:      Vibration frequency( cpm )= a   0 + a   1 × HS ( m/s )+ a   2 × HS ( m/s )/ T (second)  (2)    where symbol HS denotes the head speed, symbol T denotes the downswing time amount, and symbols a 0 , a 1 , and a 2  denote constants.    
   
   
       6 . The method of selecting a golf club shaft according to  claim 5 , wherein: 
 the constant a 0  is within a numerical range of 74±20;    the constant a 1  is within a numerical range of 5.5±1.4; and    a 2  is within a numerical range of −0.38±0.1.    
   
   
       7 . The method of selecting a golf club shaft according to  claim 1 , wherein: 
 the golf club includes a grip portion;    a three-dimensional magnetic sensor that is sensitive to magnetism within a magnetic field and outputs position and direction information, is fixed to the grip portion of the golf club head;    a predetermined magnetic field is formed during the golf swing of the golf club;    the top point in time when a downswing begins during the golf swing and the golf ball striking point in time are determined using the position and direction information output from the three-dimensional magnetic sensor; and    the downswing time amount is found from the top point in time and the golf ball striking point in time.