Notes on shaft properties - flex torque, kick-point ...

Shaft properties, including flex, torque, kick-point (bend or flex point), shaft length and weight, play important roles in affecting the balance and feel of golf clubs as well as ball trajectory. Particularly, graphite shafts come with a wide range of specifications, and are acknowledged to be very beneficial for improving our game. Drivers with graphite shafts have enabled average golfers to hit more consistently and longer balls off the tee. While steel shafts for drivers in general weigh roughly 90-120 grams, graphite shafts are generally lighter. The shaft weight of 65 grams seems to be the most popular weight nowadays while it ranges mostly between 50 grams and 90 grams (ultra light graphite shafts are less than 40 grams). The torque of steel shafts is at around 3.0, while that of graphite shafts could be as low as 2.0 and up to 12.0. As to the kick-point, graphite shafts are more versatile, too. However, steel shafts are rather popular in the applications for irons, and today's steel shafts could be very sophisticated.

Advanced shaft technology is a result of the advancement in new material development and its applications. It appears that the recent trend in the market is not lighter shafts with consistent properties in torque and strength, but rather more performance oriented considerations such as lower torque, damping effect, or application of flow design. These changes are seen in both steel shaft and graphite shaft markets.

[b]Balance and Feel[/b] - In assessing shaft performance, it is important to understand that a combination of flex, torque, kick-point, club weight and swing-weight, given a certain club-head (weight, center of gravity and gravity angle) determines the balance and feel, and consequently the performance of a golf club. Today's golf club manufacturers provide a wide range of combinations to choose from. Let's take a look at the case of Titleist 975D Titanium Driversicon, which comes with 5 different types of graphite shaft with a variety of flex (a total of 20 different shaft selections).

Flex and Frequency Matching - A general guide line for shaft flex selection is: 70 - 90 mph driver head speed = R; 90 - 100 mph = S; excess of 100 mph = X. Shaft flex can be determined by the vibration frequency, which is measured by fixing the butt of the shaft and attaching a 10-ounce weight on the tip of shaft and then vibrating it to the vertical direction. If the number of vibration or frequency is 280, the flex is defined as 8.0, and likewise the frequency of 260 becomes 6.0. Although there is no standard in the industry, generally for drivers, R is 5.5 and S is 6.5. Short irons are equipped with higher frequency shafts. The frequency matched golf clubs are built with shafts of synchronized vibration frequency throughout the set. (see "flow design" for more information).

Torque - Shaft torque describes how much a shaft would twist given a certain twisting force (1 oz weight is used for the measurement). A proper shaft torque in relation to the shaft flex, kick-point as well as club-head weight and position of CG influences your ability control ball trajectory. In principle, the lower the torque, the harder the feel and the less twisting feel (club-head turning around the shaft). Shaft torque of steel shafts does not vary too much, at around approximately 2.0, but that of graphite shafts varies more. It varies in the range of 1.8 to 12.0, although 3.5 to 5 appear to be the most common graphite shaft torque. If the torque of a shaft is less than 3, it is considered as a low torque shaft in general. Low torque, stiff shafts are difficult to use without sufficient head speed, while with a higher head speed, a high torque soft flex shaft causes off the target shots to the left. Without a sufficient club-head speed, a stiff low torque shaft tends to cause a push to the right.

Kick-point - It refers to a maximum bending point of the shaft, and it is also called flex-point or bend-point. The lower the kick-point, more tip-flex the shaft, which in turn makes you feel that the club-head moves more through impact, while a high kick-point shaft tends to make you feel the opposite. However, a high kick-point shaft is much easier to control the direction. Since more golf clubs are made with low center of gravity club-heads, low kick-point shafts seem to have lost its role to play to some extent.

Shaft Diameter Standard shaft diameters are 0.600" at butt, and 0.335" at tip for woods and 0.370" for irons. Two noticeable shaft technologies were introduced by Taylor Made ("Bubble Shaft") and Wilson ("Fat Shaft"). Wilson claims that the Fat Shaft employs larger tip diameters for better torsional stability, and therefore increasing the accuracy. While the standard shaft tip is 0.370", the shaft tip of Fat Shaft is 0.500", and the recent model offers even larger diameter at 0.540". Consistency in shaft torque (normally lower torque) appears to become available by making the shafts with larger diameters. Particularly, the larger tip diameter is effective in making shaft torque lower. However, it has to be understood that larger tip diameters make the kick-point higher.

Shaft Length and Weight - The standard shaft length is 35.5" for 9-iron and wedges and 43" to 50" for driver. While the standard shaft length of driver was 43", many drivers are equipped with 45" shafts and occasionally even longer. (The maximum legal length of a shaft is 48".) Long irons such as 2-irons and 3-irons come with 39" shafts. As to weight, most steel driver shafts weigh between 90 to 120 grams, while graphite shafts are between 65 to 90 grams, with many ultra-light models weighing less than 60 grams or less up to approximately 40 grams. The weight of traditional shafts for irons vary in accordance with the length of shaft. The incremental for 1 club is normally 0.5", and the incremental weight is around 2 grams. The shaft weight of conventional long irons is approximately 120 grams, while that of short irons is approximately 110 grams.

Flow Design - Modern technologies allow designers to control more over variables in shaft properties. True Temper, for example, offers the new product named "TRI GOLD", which provides unique features in weight, flex and kick-point - totally different from the traditional concepts. Normally shorter the irons, the lighter the shaft (as much as the length of shafts). However, the mass of each TRI-GOLD shaft increases as the shaft lengths get shorter. The company calls it "Ascending Weight" technology. It also offers a technology named "Progressive Flex" which is to optimize the variation of flex throughout the set - shorter the shaft, stiffer the shaft. In addition, it offers so called "Tri-Step" design pattern for the different tip action, or kick-point, in each shaft optimizing ball flight for each club (lowering the kick-point for a longer club).

BiMATRX - Recently, True Temper has introduced a new shaft that combines a high modulus graphite shaft with a special steel alloy tip. The Company claims that the new design realizes a light weight shaft with the consistency and torsional stability of steel shaft. It is designed to deliver the distance advantage of graphite and reduces dispersion by up to 40 percent. The shafts are designed for the use of drivers and fairway woods. The shaft weight ranges from 73 grams to 77 grams (firmer the shaft heavier the weight), and the shaft length is 46" for drivers and 44" for fairway woods. For more information, visit www.truetemper.com

Other Factors - Also, it is important to know the fact that the shaft torque and the effect of that to the golf swings is influenced particularly by club weight and the factors determined by the position of center of gravity (explained separately). It is the feeling, not specific properties such as shaft flex, kick-point, and torque, that influences the performance of each individual golf swing. Golfers should find right combinations of a number of factors. For those who lack club-head speed, extra yardage is always a premium. Needless to say, longer golf shots require faster club-head speed at impact. Lighter golf clubs with longer shafts help golfers get a faster club-head speed. The length of golf shaft is another factor when looking for the right combinations of the above factors.


Shaft Manufacturers - True Temper, Royal Precision, and Aldila are the most prominent shaft manufacturers in the U.S. True Temper offers a full range of shafts from steel and titanium shafts to graphite shafts. "SensiCore", the vibration damping steel shaft is the top of the line in steel shafts. Royal offers step-less "Rifle Shafts" which are built through the Frequency Coefficient Machining. Aldila is famous for its graphite shafts. The tour grade series is a complete line of high performance graphite shafts designed for better players. Other American shaft manufacturers include Apollo, Fenwick, Grafalloy, Harrison, Innovative Graphite, Penley Sports, Phoenixx, Rapport, and UST. Japanese shaft manufactures such as Fujikura and Graphite Design have become very popular
nowadays.


Torque is a twisting force. Imagine a screw cap on a bottle of wine (some good ones nowadays come without a cork). To remove the cap, you would need to twist it with enough torque to break the seal.

In golf, torque measures a shaft's resistance to twisting. Some shafts may only twist 2° (low torque), while others may twist 6° (high torque). The torque varies in graphite shafts, depending on how the fibers that make up the shaft are oriented. (Steel shafts do not vary enough to worry about.) Low-torque shafts are generally more difficult to make and more expensive because the graphite fibers must be carefully oriented to maintain the proper weight and flex.

The correct "twisting stiffness" is important because the clubhead must rotate on the downswing into the proper hitting position. For 99% of golfers, a shaft with 3° to 4° of torque is sufficient. Some very fast swings (120 miles per hour or higher) may need very low torque shafts.

Now for kick point. If you were able to push on both ends of a shaft at the same time with quite a bit of force, it would bend under the load. Because the shaft is tapered, it would bend at a point closer to the smaller-diameter tip end than to the larger-diameter butt end. A low-kick-point shaft has this flex point closer to the tip and produces a higher launch angle; a high-kick-point shaft has this bend point only about 5 inches from the low kick point, closer to the butt end of the shaft, and produces a lower launch angle.

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