Shaft Fitting
When it comes to shaft fitting, players have a variety of options. Characteristics like weight, flex, and torque can affect how a shaft feels and how it performs. For irons and drivers, the shaft type and its characteristics can have a significant effect on the sensation a player experiences during the swing and impact, while also influencing the launch and spin characteristics that can be achieved. This article aims to educate the reader about some of the different elements that characterize driver and iron shafts and present insights into why shaft fitting is important.
Shaft Elements
Although shafts are typically categorized by an overall flex, there are many shaft parameters that influence the way a shaft feels and performs. Below is a list of some of the most common parameters that are used to characterize a shaft, along with a brief description of what they are and how they may influence performance.
Flex
The flex of a shaft can be a fairly complex characteristic. The holistic characterization of the flex of a shaft is something called an EI profile. An EI profile presents the local stiffness of a shaft, from one end to another. In most environments, more general terms are typically used such as stiffness, butt stiffness, and tip stiffness. These values represent an average stiffness of different regions of a shaft, or an overall average stiffness. The following measurements are some of the most common.
Static Flex: There are two methods that are typically used to characterize the overall stiffness of a shaft. The first is what I would call a static-flex measurement. This is basically a cantilever loading where the shaft is clamped at the butt end and a load is applied to the tip. The amount the shaft bends corresponds to its stiffness. In general, a Ladies flex will bend much more than an X-flex using this method. In many cases the softer the overall stiffness, the greater the launch angle and spin rate. This is not always the case, as players can respond differently to variations in stiffness. This will be expanded upon in one of the following sections.
Frequency: The second method is more of a dynamic measurement, where the shaft is clamped at the butt end, and the shaft is pulled and released with a weight on the tip end. This causes the shaft to oscillate back and forth. Generally, the faster it oscillates, the stiffer the shaft. Shaft mass can also slightly affect this measurement. If two shafts have the same static flex, but one is significantly heavier, the heavier shaft will have a slightly lower frequency measurement than the lighter one. Changes in frequency have a similar effect as static flex on performance.
Tip Flex: Tip Flex, or Retro Flex, represents the average stiffness toward the head side of the shaft. Sometimes this is measured in a very similar fashion as the static-flex measurement. The difference being that the tip end is clamped and the load is applied to the butt end of the shaft. The more a shaft bends in this configuration, the softer the tip. Tip flex has a similar effect on performance as static flex, in that the softer the tip the greater the launch angle and spin rate.
Kick Point
Kick point is essentially another way to talk about the difference in tip stiffness and butt stiffness in a shaft. The softer the tip is compared to the butt end, the lower the kick point, and vice-versa. As one could gather from the above discussion on flex, the lower the kick point, generally the higher the launch and spin characteristics for a shaft.
Weight/Balance Point
The overall weight of a shaft and its center-of-mass can play roles in performance. These characteristics are pretty much the easiest to measure since all that is required is a scale and a knife edge (or 2 scales). Both metal wood and iron shafts can come in a range of weights and balance points.
Overall weight is typically the first characteristic a player notices when trying various shafts. Some players have a strong preference for a heavier or lighter shaft. We have seen in testing that a heavier shaft can promote lower ball flights with more left-to-right trajectory while lighter shafts can promote higher ball flights with more right-to-left trajectories. It should be noted that the easiest way to make something stiffer is to add more material, so in many cases weight and stiffness can trend together.
Iron shafts offer a choice between graphite and steel. Graphite will typically play lighter, and is great for players who struggle to get enough club head speed with steel or who would like to minimize the harshness that can sometimes be prominent on mishits with a steel shaft. Steel shafts are available in a variety of weights and can produce a range of impact sensations.
Another shaft term that has become quite common in the fitting environment is counter balanced, or high balance point. One benefit of a high balance point or counter balanced shaft is it allows for more head weight without drastically affecting the swingweight of a club. These types of shafts typically promote a bit of a higher launch angle, and are available as aftermarket options as well as stock in some OEM models.
Torque
Of all the characteristics that can describe a shaft, torque is the one I receive the most questions about. There seems to be a pretty strong sense that if a shaft is lower torque (more torsionally stiff), it is somehow better. I have yet to see evidence that this is true. It is true, however, that making a shaft with lower torque can be more difficult, and as a result can lead to a more expensive shaft. One way to measure torque is to clamp one end of the shaft and apply a constant couple-moment (turning force) to the other end. The more the shaft twists, the higher the torque.
Having conducted testing on shaft torque, we know that it affects both feel and performance. One of the clearest insights from testing is that shafts with lower torque FEEL stiffer and shafts with higher torque FEEL softer, even when the EI profiles (stiffness) are pretty much the same. From a performance standpoint, there was little difference (at least statistically) between shafts of high and low torque. There did appear to be some minor evidence to suggest shafts with lower torque delivered the face more shut, while shafts with higher torque delivered the face more open relative to path. Even though there was some slight evidence in the data, if this effect is really present it is extremely small.
Is Shaft Fitting important?
There are a number of reasons why shaft fitting is an important component of most any fitting, and something all players should consider before purchasing new equipment. Here are a couple reasons why I feel one should make it a priority to be fitted for a shaft.
All Flex codes are not created equal
In previous articles on iron and driver fitting, I discussed the reality that the flex codes labeled on a shaft (e.g. R, S, X) can adversely influence a fitting. Not only can the flex code elicit an unfair emotional response from a player who may perceive a softer flex as a reflection of their strength or ability, but there is no standard for these codes. Two shafts with different flex codes may, in actuality, have very similar flex. This is depicted in Figure 1, which shows the Trajectory Effect of a shaft (discussed in a following section) and the Flex. Studying this figure and the overlap of flex codes, it is clear that there are some R-flex shafts masquerading as S-flex shafts. It should be noted that on the PGA tour, where players generate plenty of club head speed, the flex of iron shafts spans a range from R-flex to X-flex. As a player being fit, do not allow the flex code to cloud your judgement regarding which shaft will lead to the best performance.
Figure 1: Shaft Trejectory Effect vs. Flex
New Model? Might need a new shaft.
Another important thing to note is just because a shaft worked well with one driver model or set of irons, does not mean it will perform optimally for the same player in another model. The way a shaft behaves and delivers the club head depends on the characteristics of the head itself. The mass properties of the head (things like total mass and center-of-mass location) can change quite a bit from model to model. As a result, a player may find that one shaft works really well in one model, but another shaft works best in another model.
You might not always see what you expect
In the previous section, I described some of the elements that can characterize a shaft and how, IN GENERAL, varying these elements can influence ball flight. One challenge with fitting is that the player and club do not always behave in a predictable manner. For example, two players who appear quite similar can react differently to changes in shaft characteristics (e.g. stiffness).
An informative academic paper that exemplifies this phenomenon, written by Dr. Sasho MacKenzie, is entitled “The Influence of Golf Shaft Stiffness on Grip and Clubhead Kinematics1”. This paper presents a study conducted using a motion-capture system where participants hit drives with an R-flex driver shaft and a more rigid X-flex shaft. One of the more common notions held by club fitters, and something we have seen in our own testing, is that more-flexible shafts can generally lead to higher launch angles. Although this may hold true in a number of situations, the effect may vary drastically from player to player. MacKenzie found that there was a significant difference in the deflection of the shaft at impact (in the loft direction) and shaft handle lean. The R-flex shaft functionally added 2° more loft through lead deflection. However, the actual mean delivered loft the ball saw for the R-flex shaft was only 0.4° higher, and was not statistically significant. These results can be seen in figure 2. Essentially, some players compensated for the added shaft lead with the regular flex by delivering the handle with more forward handle lean, which competes with the added loft from the shaft. In some cases the R-flex shaft was actually delivered with less loft. Others kept a similar handle lean, and did see higher delivered loft numbers with the R-flex shaft.
Figure 2: Effect of Shaft Overall Stiffness on Club Head Delivery
All this shows that players may alter the way they swing a driver based on the feel and feedback they receive from the shaft. Ongoing research looks to understand and predict how players react differently to inputs such as shaft stiffness. This again highlights the importance of shaft fitting. There are some general shaft-fitting behaviors that on average hold to be true, but there are always exceptions. Comparing shafts in a fitting environment and examining actual performance data is still the best-case scenario since you may not always get the results you expect.
Choosing a Shaft
So, with all this information on shafts, how does one begin to understand what type of shaft might be best for them? There are definitely some ways to start to narrow down the type of shafts that may be best for you, and allow you to enter into a fitting with an idea of what might be best. Typically, fitters will base an initial driver shaft recommendation on a player’s swing speed and/or distance. Although other factors (tempo, transition, impact position, etc.) will influence shaft recommendations, club head speed is a decent starting point. As you try different shafts, the fitter should solicit feedback about feel (flex, weight, impact) and performance, and evaluate how each shaft affects ball flight.
I feel one of the best ways to look at a range of shaft offerings is to plot the Trajectory Effect of a shaft against the Flex. An example of such a chart is shown in figure 3, which at PING we call a Shaft Visualization Chart. The Trajectory Effect is a number we use that considers the effects of all the different elements (flex, torque, weight, etc.) and provides a relative measure of how a shaft on average might compare to another. The Flex is basically the static flex of the shaft. In general, every 10-point increase in Trajectory Effect will increase the launch angle by 1/3 of a degree and the spin rate by 100 rpm with a driver. We have found that players will end up “getting along” with shafts in specific regions of a chart like this. Even though there might be some subtle differences in the shafts someone might need when changing the head model they are using, one does not move to extremely different regions.
Figure 3: Shaft Visualization Chart
Let me talk through an example of what it might look like to understand where you would find yourself on a chart like this. In a simplified sense, we use 3 different characteristics to determine what region of this chart someone would find the best shafts for them.
- Club Head Speed: We typically would start with club head speed (CHS) to try and understand a general region of flex that may work best. So someone with a driver CHS around 105 mph on average would do best with a shaft having a flex value around 3.5. Without considering any other aspects of this player’s swing, a shaft sitting somewhere in region A on figure 4 would have the best chance of performing well for this player.
Figure 4: Shaft Visualization Chart with Example Regions - Loading: The initial part of the downswing plays a fairly big role in the stiffness profile that is optimal for a given player. Players who exert concentrated, high levels of force and torque during this phase of the downswing typically do better with a shaft that plays a bit stiffer than CHS alone would suggest. Conversely, players who are a bit more gradual in their loading of the shaft typically get along with shafts that are a bit softer. Let’s say our example player loads the shaft gradually, and more along the length of the shaft. This would shift the region upwards and to the right to region B on figure 4.
- Handle Lean at Impact: The last of the three parameters that we use to determine the appropriate region on the shaft visualization chart is the position of the hands at impact. Looking at a general handle location can influence whether shafts with higher or lower trajectory numbers will perform best for a particular player. If we look at our example player and realize he is someone who generally delivers the driver with a lot of forward shaft lean, the region of shafts that would most likely perform best would move upward, into region C on figure 4.
It should be noted that this philosophy of leveraging swing characteristics is based on average behaviors across large samples of players. Finding a region on a chart like the shaft visualization chart provides a high probability of converging on the best shaft, but as was discussed earlier in this article, you may not always see what you expect. Validating shaft choices with actual ball flight will always provide the highest level of confidence in a choice of shaft. To help determine the region of the Shaft Visualization chart that may be right for you, start with the club head speed numbers located at the top of figure 3, and then move around based on your specific swing and preference.
PING Fitting Example
Figure 5 shows the difference in dispersion between the shafts, and table 1 shows the ball-flight data. On average the R-flex produced a much higher launch angle with a little bit more spin. This ultimately led to 11 more yards of carry and 7 more yards of total distance. The extra launch and spin helped boost carry distance, even though the average ball speed was down 1 mph. The steeper landing angle led to slightly less roll-out, but the net gain was still significant. In addition to the gain in distance, the player’s dispersion area shrunk significantly.
Table 1: Ball Flight Data From Shaft Fitting
The resulting differences can not only be attributed to the way the shaft was bending, but the way the player was responding to the shaft. The combination of shaft deflection and the way he delivered his hands to the ball with the R-flex shaft led to some compelling results. It should be noted that this is a single example comparing two significantly different shafts. Although results between shafts may not always but this drastic, this shows the sort potential that lies in a shaft fitting.
PING Staff Player Example
One of the benefits of conducting research at a major OEM is the exposure to a huge range of swings, abilities, and research tools. In particular, tour players on staff provide a fantastic pool of players to examine with tools like motion capture and high-speed video. Many times when working with a staff player, the data and results are purely for our use as scientists and engineers to support research projects and club designs. In other instances, this time is spent trying to answer questions that arise from the player during the fitting process or from on-course experiences.
Figure 6: Impact Heat Map Comparison of Shaft A to Shaft B
In one particular instance, one of our staff players was trying to understand and validate some of the things he was feeling when comparing two different iron shafts. Both were constant-taper iron shafts with labeled flex codes that were similar. He had a sense that one was performing a bit better than the other, but was not completely sure he wanted to switch from his current shaft (shaft A) to a new shaft (shaft B). To help provide some insights, we compared the two shafts using a motion-capture system. After having the player hit ten shots with each shaft while alternating clubs through the process, we spent some time looking at the results. Figure 6 shows a comparison of the impact pattern for the two different shafts. It was immediately apparent that shaft B was leading to a much tighter impact pattern on the face. In addition to the tighter impact dispersion, the player was able to deliver the club head with a mile-per-hour greater club head speed on average with shaft B. The tighter impact dispersion and increased club head speed ultimately led to a decrease in dispersion landing area and greater carry distance, as seen in figures 7 and 8. This helped validate what the player was seeing on the range, but also demonstrates why shaft fitting is important. It can definitely affect performance!
So the next big question is, “Why did shaft B perform better than shaft A for this player?” After evaluating the data produced by the motion-capture system, it was clear the shafts where loading and unloading in a different fashion. The difference in actual dynamic deflection of the shaft during the downswing influences the sensation the player experiences, and can lead to kinetic responses that vary in consistency, timing, and magnitude. Ultimately what I am saying is that players tend to “get along with” different dynamic bending profiles, leading to more-consistent performance and sometimes more-efficient delivery of the club head, a behavior that was also evident in the previous fitting example. This is a great instance of how different shafts can lead to significantly different results, even when the two shafts look similar and have similar flex codes.
Summary
The study of how shafts influence the delivery of the club head and the way they can elicit different responses from a player is complex. It is something that the industry and scientists in academia are continuing to research and understand. Even though this is the case, being fit for a shaft can be extremely fun and lead to improved performance on the course. It is something all golfers should spend some time doing if they desire to improve their game. Hopefully this article has given you a good idea of the importance of shaft fitting, the different elements of a shaft and how they may affect performance, as well as how swing characteristics can be used to converge upon an optimal set of shaft options.
1 MacKenzie, S. J., Boucher, D. E. (2016). The influence of golf shaft stiffness on grip and clubhead kinematics. Journal of Sports Sciences, Accepted Feb 18, 2016.
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