Golf club shaft

Abstract

The present invention provides a high-balance-point shaft capable of increasing ball speed. A golf club shaft formed by laminating fiber-reinforced resin, wherein the balance point obtained by formula below is set to be 53% or higher; and the kickpoint obtained by formula below is set to be 44% or higher.

What is claimed is: 
     
         1 . A golf club shaft formed by laminating fiber-reinforced resin,
 wherein the balance point obtained by formula (1) below is set to be 53% or higher; and   the kickpoint obtained by formula (2) below is set to be 44.5% or higher and 48% or lower, .   wherein the mass of the shaft M [g] and the full shaft length (L S ) [mm] satisfy the following formula,
   35≦M×(L S /1168)≦75
 
   balance point (%)=(L G /L S )×100   (formula 1)
 
 L G : distance from the gravity center of a shaft to the tip end of the shaft 
 L S : full length of the shaft
   kickpoint (%)=(L K /L B )×100   (formula 2)
 
 
 L K : when a shaft is curved by a compression load exerted on both ends of the shaft so that the linear distance between both ends is 98.5˜99.5% of the shaft length, the distance from the tip end of the shaft to a point where a straight line connecting both ends intersects with a perpendicular line drawn from the apex of the curve. 
 L B : when a shaft is curved by a compression load exerted on both ends of the shaft so that the linear distance between both ends is 98.5˜99.5% of the shaft length, the linear distance between both ends of the shaft, 
   wherein the shaft is formed in a tube shape; the inner diameter of the shaft tapers, gradually increasing from the tip end toward the butt end; the inner-diameter taper has an inner-diameter taper bending point (Pm); the inner-diameter taper bending point (Pm) is positioned at 550˜750 mm from the tip end of the shaft; and when an inner-diameter tapering gradient is set as (Tm) to indicate the inner-diameter inclination between the tip end and the inner-diameter taper bending point (Pm), and when an inner-diameter tapering gradient is set as (Tb) to indicate the inner-diameter inclination between the inner-diameter taper bending point (Pm) and the butt end, Tm>Tb is satisfied, and   wherein the inner-diameter taper has an inner-diameter taper bending point (Pt) positioned 40˜140 mm from the tip end of the shaft; and when an inner-diameter tapering gradient is set as (Tt) to indicate the inner-diameter inclination between the tip end and the inner-diameter taper bending point (Pt), and when an inner-diameter tapering gradient is set as (Tm′) to indicate the inner-diameter inclination between the inner-diameter taper bending point (Pt) and the inner-diameter taper bending point (Pm), the following are satisfied:
   Tt<Tm′
 
   0.1/1000≦Tt≦5/1000
 
   
     
     
         2 . A golf club shaft formed by laminating fiber-reinforced resin,
 wherein the balance point obtained by formula (1) below is set to be 53% or higher; and   the kickpoint obtained by formula (2) below is set to be 44.5% or higher and 48% or lower, .   wherein the mass of the shaft M [g] and the full shaft length (L S ) [mm] satisfy the following formula.
   35≦M×(L S /1168)≦75
 
   balance point (%)=(L G /L S )×100   (formula 1)
 
 L G : distance from the gravity center of a shaft to the tip end of the shaft 
 L S : full length of the shaft
   kickpoint (%)=(L K /L B )×100   (formula 2)
 
 
 L K : when a shaft is curved by a compression load exerted on both ends of the shaft so that the linear distance between both ends is 98.5˜99.5% of the shaft length, the distance from the tip end of the shaft to a point where a straight line connecting both ends intersects with a perpendicular line drawn from the apex of the curve. 
 L B : when a shaft is curved by a compression load exerted on both ends of the shaft so that the linear distance between both ends is 98.5˜99.5% of the shaft length, the linear distance between both ends of the shaft, 
   wherein the tip-side end of a weight layer (W) that weights 10˜30% of the shaft weight is positioned at 800 mm or greater from the tip end of the shaft, and the flexural modulus of the weight layer (W) in a longitudinal direction of the shaft is 70 GPa or lower, wherein the average thickness of the weight layer (W) is set at 0.5 mm or less, and the weight layer (W) is preferred to be disposed on the sixth layer from the outermost layer or closer, and   further comprising an angle layer made of fiber-reinforced resin where the fiber orientation is set diagonally to the longitudinal direction of the shaft; the weight layer (W); a straight layer made of fiber-reinforced resin where the fiber orientation is set to be parallel to the longitudinal direction of the shaft; and a hoop layer where the fiber orientation is set to be perpendicular to the longitudinal direction of the shaft.   
     
     
         3 . The golf club shaft according to  claim 2 , further comprising a reinforcement layer made of fiber-reinforced resin, wherein the reinforcement layer is disposed 400 mm or less from the tip end side of the shaft, and its fiber orientation is set to be parallel to the longitudinal direction of the shaft.