Is the Shaft the Engine of the Golf Club?
BY Tom Wishon
If I’ve heard it once, I’ve heard it a hundred times that the shaft is the “engine” of the golf club. While I’ve been working to understand the real performance of the shaft in the club since the 1970’s, it has only been in the past five years that our work has led us to the point that we truly feel we know and understand precisely what it is, and equally what it is not, that the shaft does in the execution of a shot.
In short, the shaft is not the engine of the club. The golfer is truly the engine, while the shaft is better thought of as being the “transmission.” In an automobile, the engine generates the power; the transmission sends that power to the axles and the wheels to be able to propel the car down the road. In golf, the golfer is the whole and complete source of the power that drives the ball down the fairway. The shaft is simply one of the elements in the club that delivers all or only a part of that power to the ball.
The shaft cannot increase the power from the golfer that is delivered to the ball. However, the shaft can decrease that power, which is precisely what happens when the shaft is ill-fit to the size, strength, athletic ability and swing characteristics of the golfer.
Use a shaft that is too heavy and the power of the golfer will be reduced to a slower clubhead speed than would be possible with the correct shaft weight for the golfer’s ability. Use a shaft that is too light and the golfer may achieve their maximum clubhead speed, but they will lose control of the club, thus resulting in a higher percentage of off-centre hits for a loss in distance and accuracy.
A shaft that is the right weight, but too stiff or too flexible for the swing characteristics of the golfer, won’t drop the clubhead speed below the golfer’s potential, but it can affect the launch angle and swing timing to cause a loss of distance along with a loss of impact consistency and possible loss of accuracy too.
Perhaps the best way to convey the role of the shaft in the execution of the shot is to start with a full explanation of how the shaft actually bends and performs from the influence of a golfer’s swing characteristics. Key to this understanding is to accept the fact that the shaft can ONLY react to individual swing movements of the golfer. Different swing characteristics cause different shaft bending/twisting actions during the swing. By understanding what the different swing moves do to the behaviour of the shaft, golfers can then begin to realize how different shaft designs do or do not work.
Nothing Really Happens Until the Downswing Starts
From the standpoint of the performance of the shaft, the backswing has no relevance. It certainly does have a bearing on swing plane, swing path and face angle, but when discussing what the shaft does in the execution of the shot, the only role of the backswing is to rotate the club into a position such that the first bending action of the shaft will happen in what we call the “toe-up/toe-down” or, “6 o’clock/12 o’clock direction of the shaft in the club as shown in Fig 1.
The starting move of the downswing is called the “Transition.” Depending on the golfer, the transition can be sudden and forceful as if the golfer wants to apply a lot of force very quickly to start the downswing, it can be slow and smooth so the golfer gradually builds up force, or in-between. The more forceful the transition, the sooner and the greater the shaft will begin to bend. Conversely, the slower and smoother the transition, the less the shaft will begin to bend.
It is a modern principle of shaft fitting to say that the more forceful the transition, the stiffer the flex of the shaft needs to be, while the easier and smoother the transition, the more flexible the shaft should be for the golfer. This is because the more forceful the transition, the more the golfer will bend the shaft. It is very important to note that two golfers with the same swing speed can have totally different transition moves and from that, apply very different amounts of bending force to the shaft.
It is a common practice in the golf equipment industry for there to be swing speed ratings offered for different flexes within each shaft model. If these are done accurately, the swing speed rating is meant to convey the thought that for that swing speed range with an average transition force, the primary flex of the shaft will not be too stiff or too flexible.
If each shaft’s swing speed rating is created accurately, a golfer with a strong/forceful transition who applies more bending force to the shaft should use a shaft that comes from a swing speed rating that is HIGHER than the golfer’s real swing speed. Likewise, a golfer with a smooth and easy transition who applies less bending force to the shaft should use a shaft that comes from a swing speed rating that is LOWER than the golfer’s real swing speed.
What Happens After That First Bending of the Shaft?
Think about this for a moment. During a proper backswing, as we turn our shoulders and hips away from the ball, we also rotate the club with our hands/arms such that the force created by the transition move will cause the shaft to bend in a “toe-up/toe-down” or, “6 o’clock/12 o’clock direction – not in a “toward the target” direction of bending as shown in Figure 2.
How long the shaft can remain flexed after the force of the transition depends on two things in the swing. Firstly how long the golfer can retain the wrist-cock angle during the downswing and secondly whether the golfer can maintain a positive acceleration of the club through the downswing. Of these, the wrist-cock angle is of most importance. The very moment the golfer begins to unhinge the wrist-cock angle, the arms begin to slow down and any initial bending of the shaft created by the transition begins to “un-flex” or release.
The unhinging of the wrist-cock angle is called the “Release.” If the golfer has a very late release, the shaft will flex forward at the moment of impact. For golfers with a late release, the stiffer the shaft, the less the shaft can bend forward at impact. Conversely, for late release golfers, the more flexible the shaft, the more the shaft can bend forward at impact.
Whenever the shaft bends forward, the clubhead arrives at impact with more “dynamic loft” than the actual “static loft” of the head as measured in a clubhead specification gauge. Here again, the more flexible the shaft in relation to the golfer’s downswing strength, the higher the loft of the head will be at impact. The stiffer the shaft, the lower will be the dynamic loft. More dynamic loft means a higher launch angle with more backspin, while less dynamic loft means a lower launch with a little less spin.
The earlier the golfer releases the club on the downswing, the less the shaft can retain its “forward bend” position at impact. For golfers who release the wrist-cock angle very early on the dowswing, the shaft will expend its forward bend position too soon, and will arrive at impact in a straight position.
This is why golfers with a late release can see visible height differences between shafts while golfers with an early release tend to hit the ball the same height with any shaft they use. This is also why trying to use the shaft as a factor in fitting to change shot height only works for golfers with a later release.
There is one other factor which contributes to the forward bending of the shaft. The farther the clubhead’s Centre of Gravity (CG) is located behind the hosel bore, the more the shaft could bend forward and with it, increase the launch angle and spin of the shot. Clubheads with a greater amount of hosel offset and with a greater face to back size will hit the ball higher and with more spin than will heads with no offset and a smaller face to back dimension.
Do remember that none of this matters for the golfer with the very early release. The earlier the golfer unhinges the wrist-cock angle, the less forward bending of the shaft is retained by the time the club gets to impact. Hence the earlier the golfer unhinges the wrist-cock angle, the less effect any shaft OR clubhead will have on the height and backspin of the shot.
In discussing this forward bending action of the shaft, it is important to note that rarely, if ever, will the shaft arrive at impact in a “lag position” (as in Fig 3), in which the shaft is flexed backward. To do that, the golfer would have to arrive at impact with at least a part of their wrist-cock angle still un-released. Perhaps the closest example of a shot in which the shaft is close to lagging backward at impact would be Tiger Woods’ famous “stinger shot.” To hit the ball that low requires Tiger to not fully release the club as he drives his hands through impact ahead of the clubhead.
But What Does All This Mean to Fitting and Performance?
From a pure fitting standpoint, the shaft can only affect the following parameters of performance:
The Weight of the Shaft Controls the Total Weight of the Club
The weight of the shaft, controls the total weight of the club, this in turn has a strong influence on the golfer’s potential swing speed. Light shaft = lighter total weight = potentially more swing speed = potentially more distance. However, greater distance from a lighter shaft can only happen if the swingweight and length are well matched to the golfer’s swing transition, swing tempo, and swing path. If these factors are not well fit to the golfer, more off centre hits will result and from that, the golfer will LOSE distance.
The Torsional Stiffness
The Torsional Stiffness (Torque) can have a slight effect on the accuracy of the shot, but only for golfers with a strong transition move in their swing. Because the shaft is always attached to the wood or iron in the heel area of the head, a tremendous amount of the head’s mass is positioned out from the centre of the shaft. Therefore, the stronger the golfer’s transition move, the more chance there is for this head mass to twist the shaft and deliver the face open at impact. However, because most shafts today are made with a tremendous amount of torsional stiffness (torque 4Ã‚Â° or less), only the golfers with the strongest transition move need to think about using very low torque shafts under 3* to offset this possible mis-direction tendency.
Overall Flex + the Bend Profile Design of the Shaft
The overall flex + the bend profile design of the shaft can affect the launch angle, spin rate, and trajectory of the shot, but only for golfers with a later to very late release. The earlier the release, the less the shaft can have any effect on the height and spin of the shot.
The overall flex + the bend profile design of the shaft will also affect the feel of the shaft for golfers, who have enough sensitivity and experience to note such bending feel differences. For such golfers, the right bending feel is critical to the consistency of their swing rhythm and timing, and from that, supremely important to achieving the highest swing speed + on centre hit consistency.
If you have ever played with a shaft that is too flexible or too stiff feeling, what do you have to do to try to make the shaft work and feel right? You have to alter the swing, either swinging harder with a too stiff shaft to make it feel right, or slow down the swing to make a shaft that is too flexible feel better. Anytime the golfer consciously, or sub-consciously begins to change the swing to make the shaft feel match their bending feel desire, severe inconsistency in shotmaking will result.
For golfers who do have such a sense of feel, this is the most important contribution of the shaft’s flex and bend profile design to shotmaking performance. With a shaft that displays the right bending FEEL, the golfer can swing with better timing, rhythm, and with no restriction to the release of the club through impact. When that happens, the golfer will always achieve their highest possible swing speed and highest percentage of on centre hits.
A thank you goes to Rob Curtis – Trainee Pro at St Michael’s Golf Club – for his time as our swing model.