Golf Shaft Stiffness

Understanding Golf Shaft Stiffness

By Russ Ryden, Fit2Score, A Dallas Fort Worth Club Fitter & Club Maker
The Golf Center at the Highlands, Carrollton Texas

How stiff is this golf shaft? That question is on the mind of anyone who has ever been curious about their golf clubs. Club makers have been trying to answer that question for a long as I can remember.

GWorksDBI am told the first tool commonly used was a deflection board. The butt of the shaft is clamped, a weight is hung on the tip and the amount the shaft bent was used to rate the shafts stiffness. This was and still is, an excellent way to rate shafts. The problem was that none of the shaft companies used the same board. Shaft sales and marketing created a letter system, LARSX, Ladies, Amateur, Regular, Stiff, X-Stiff. Brunswick shaft company patented a numbering system 4.0, 4.5, 5.0, 5.5, etc. The golfer was and still is confused about these numbers. The club making community made their own attempt at creating a standard. To date, the only standard is confusion.

I began my journey to understand the golf shaft about 15 years ago. I now have a database containing measurements of about 3000 different shafts. For those that are looking for a simple basis for comparing shafts I have adapted a method recommended to me by Jeff Meyer, Area Under the EI curve. Jeff has spent most of his life in the golf shaft business. The idea came to him when he was the shaft guru at Acushnet Golf.

As you watch this animation, you will understand the concept.

areaillustrated_650

The best ideas are often the simplest. Area under the EI curve is easy to compute once you have the inch by inch measurement. You add them up. To compensate for shafts of different lengths you divide the sum by the length of the shaft measured. To create a simple index, I divided that number by a common factor to create an easy to compare 2 digit stiffness index.

The recent reviews presented here at Golf Shaft Reviews, give a stiffness index for each shaft measured.

One of my friends, a fellow fitter who has been working with EI graphs since the very first day I began measuring them asked why I would reduce the elegance of the EI profiles to a single number. My answer, if you are going to use a number to try to understand shaft stiffness, be it LARSX or 4.0, 5.0, 6.0 7.0. area under the EI curve is a better number. It indicates all of the shaft, not just a single point. Is it the best way we now have available? No. Knowing the shape of the EI curve and its relationship to other shafts is the best way we now have available. But without knowing and studying the EI profiles of the 3000 shafts I have already measured, it is better than the alternatives. And given that the measurements were all taken the same way with the same instrument, it transcends manufactures, models and weights.

Lets lets look at some of the other ways shaft stiffness is presented and marketed.

Shaft Frequency

The concept of using shaft oscillation frequency was discussed in the 1968 book, “Search for the Perfect Swing” by Alastair Cochran and John Stobbs. “Search for the Perfect Swing” is one of the first explorations of golf technology. In Appendix I a formula for frequency is shown as a function that included “E=an elastic property of the material of the shaft” and “I=a quantity which depends on the precise cross-section of the shaft and which represents its ability to resist bending”. As you read this article you will realize the authors were saying frequency might be useful, but the complexity of the calculation was not likely to make frequency an easy way to define golf shaft stiffness.

GWlaserCPMDr. Joe Braly introduced club makers to using the rate of oscillation of a shaft (frequency) to understand its stiffness. In the 80’s he did research on the PGA tour. He used a frequency instrument to measure the shafts used by the tour players. From this research, he developed a formula for the stiffness of ratio of the different irons in the set. The ratio he found was 4.3 CPM (cycles per minute) per one half inch of length of club.

FrequencyStrainGaugeInspired by the research done by the Braly’s, a club makers organization, the PCS, endorsed and taught frequency based club making to its many, many members. it was a time when shaft design was not as complex as it currently is and when frequency instruments were one of the few tools available to club makers for measuring shaft stiffness.

The PCS recognized that frequency measurements were affected by clamp pressure, clamp length, weight and the actual instrument being used. They established a standard primarily focused on one of the instruments. Software knows as “The Equalizer”  was sold to PCS members. It came with a calibration stick that was used to standardize the readings to a common denominator across instruments. During its dominance as a club makers organization the PCS did not promote discussion of alternative shaft stiffness systems. Nor did it inform its membership that the shaft designers and manufacturers primarily used EI for understanding shaft stiffness.

Let’s take a look at an EI chart of three shafts with the same frequency.Each of these shafts has a frequency of 354 on my instrument. I use a pneumatic clamp, clamped 7″ from the butt of the shafts. These are 6 iron shafts and were measured with a 261 gram 6 iron head. Seven inches, the Fujikura standard, is still used by some club manufacturers and shaft companies.

CPMSameEIDifferent As you can plainly see, these three shafts which have exactly the same frequency are quite different when viewed with EI analysis. Tom Wishon, then at GolfSmith, recognized that butt frequency alone did not work. He measured frequency at several points down the shaft while sorting a box of iron shafts for a set he was building for a PGA tour pro. That evolved into a system of measuring the shaft with a frequency instrument at different point down the shaft. With that, the term ‘shaft profiling’ was born. That system was flawed in more ways than I want to discuss here. It gave very crude charts of stiffness down the shaft when compared to EI charts. If you want to understand the relationship and the difficulty of using frequency to estimate EI read page 205 of Cochran & Stobb that I referred to at the beginning of this section.

Shaft frequency is not of much use in evaluating shaft stiffness. The problem for club makers and fitters who recognized the importance of shaft profiling was that there was not an affordable EI instrument until I designed and manufactured one. They used the frequency instruments they had. As with all technologies, instruments and expertise evolves. Frequency profiling and frequency rating of shaft stiffness were an attempt by club builders to reverse engineer shaft knowledge not shared by the shaft companies. Affordable EI instruments have closed the knowledge gap between the shaft engineer and the club fitter.

Shaft Stiffness Labels – LARSX

Most shafts have a stiffness label. These labels are referred to as LARSX by club makers, Ladies, Amateur, Regular, Stiff, X-Stiff. As we all know, there is no standard for assigning stiffness between manufacturers. But what you may not realize is that there is no standard for assigning these labels to different products made by the same manufacturer. Let’s look at three different KBS shafts all labeled S flex.

MFGstiffAs you can see, the KBS 120 gram Tour and C-Taper have very similar stiffness at the butt. The 110 gram C-Taper Lite also labeled S flex is much softer throughout the shaft. This is quite common. KBS shafts were at hand when I was measuring and creating charts for this article, they are not unique in this practice, all shaft companies do this. To make any sense out of shaft company labels you must recognize that LARSX refers to shaft stiffness of that particular model and weight, It does not apply to shafts of different models or weights.

What you might have started to notice here is that Jeff Meyer’s system, area under the EI curve, as a single metric rating system, actually makes some sense.

Shaft Stiffness Labels – 4.0 ~ 4.5 ~ 5.0 ~ 5.5 ~ 6.0 ~ 6.5 ~ 7.0

The Rifle shaft produced by FM precision/Brunswick/Royal Precision (different names, same company) introduced and patented a numeric stiffness rating system. It was a detailed system for relating swing speed to shaft stiffness. Using shafts that were both weight and frequency sorted in the factory, the club maker made iron shaft sets by matching swing speed to shaft stiffness. It was revolutionary in its day. The first systematic attempt at shaft fitting. There are many club makers that still use the Rifle system or variations of it.

The Royal Precision shaft company was purchased by True Temper and with that purchase was the numeric stiffness rating patent. Here is a look at how that system is currently applied.

MFGnumbers1

Two shafts, the Project X and the Project X LZ are both labeled 6.0. The EI measurement clearly shows these shafts have different stiffness. Once again, we see that stiffness labels on shafts show the difference in shaft stiffness within models not between models.

Now, let’s loop back to butt frequency and add another shaft to this chart.

MFGnumbers2

The frequency of these three shafts is Project X 5.0 = 350, Project X 6.0 = 363 and Project X LZ 6.0 = 349. Notice how the Project X 5.0 and the Project X LZ 6.0 are similar in the butt area, having the same butt frequency. They are quite different in the mid zone. And once again, take note of the EI area rating of these two shafts.

Conclusion

Back to the question posed in the opening sentence of this article, How stiff is this golf shaft? The  systems we have to rate golf shaft stiffness do not work across brands or even across models within brands. Most experienced club fitters use their experience to understand golf shaft stiffness. Many use some systematic method, most often frequency, to rate the shafts they work with. Then with that rating in mind, they test golfers performance and reaction to various shafts. A sense of what works and does not work develops through experience and is indexed by the shaft labels or their shaft stiffness rating method. The current key to understanding shaft fitting is experience. Years of experience. Because there was no current system that accurately indexes the stiffness of the golf shaft.

Now, thanks to Jeff Meyer, there is.

Project X Iron Shaft Review

Rifle Project X Iron Shaft Review

By Russ Ryden, Fit2Score, A Dallas Fort Worth Club Fitter & Club Maker
The Golf Center at the Highlands, Carrollton Texas

RifleProjectX_image

The Precision Rifle Project X has been with us for a very long time. It somehow got missed when I was in the early days of measuring the vast number of shafts in the market. I noticed its absence when I measured the Project X LZ model. It was originally made by Royal Precision Shaft Company in Connecticut. They were acquired by TrueTemper and the production was moved to Tennessee.  You will see many of the best players in the world playing this shaft. Compared to a Dynamic Gold X100, it is slightly softer in the butt and stiffer in the Mid. Unlike the TrueTemper Dynamic Gold, the  Project X profile is the same for all weight/stiffness variations. The heavier the shaft the stiffer it gets. The profile remains the same for all flex designations.

Lets look at the profile:

The measurements are available only to registered readers

My friend and mentor, Dave Tutelman posted this comment in another discussion of the shaft stiffness range metric. I cannot express my thoughts about this new metric any better than he did. “A big advantage of “measuring” shaft stiffness by plotting the EI curve is that you can do mathematical operations like this. You chose a simple one, with simple arithmetic. But it isn’t that hard to use a butt-biased weighting function that will predict frequency, or a tip-biased weighting function to predict trajectory height. The combination of a known EI profile and spreadsheet capabilities means it’s just arithmetic. As we understand shafts better, EI will not become obsolete; just the way we use and display it will.”

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Dynamic Gold AMT – Tour Issue – Golf Shaft Review

Dynamic Gold AMT Iron Shafts

By Russ Ryden and Mark Maness

By Russ Ryden, Fit2Score, A Dallas Fort Worth Club Fitter & Club Maker
The Golf Center at the Highlands, Carrollton Texas

DGAMT_Image

AMT stands for Ascending Mass Technology. It is not a new concept. Ping has had ascending weight shafts for many years. Nippon 999’s were ascending. Aerotech Players Spec were ascending. If you are not a club maker you probably have not been exposed to the concept. Briefly, there are primarily two kinds of shafts; constant weight tapers and parallel’s. Constant weight tapers are made to length in the factory and the shafts in the set are all the same weight even though they are different lengths. Parallels are made to one length in the factory. The club maker cuts them to the length needed for the club he is building. As they are cut shorter they weigh less. The shafts in a set are lighter in the short irons than in the long irons.  I wrote an article about this some years ago in the technical stuff section of this site; Constant Weight vs Parallel Iron Shafts.

Iron heads get heavier as the the numbers get higher. The 4 iron head is heavier than the 3 iron, the 5 iron is heavier than the 4 iron and so on down to the gap wedge. In sets made of parallel shafts, the shafts get lighter while the head gets heavier. In sets made from constant weight shafts, the shafts are the same weight while the heads get heavier. In ASCENDING WEIGHT sets, the shafts get heavier as the heads get heavier. This has always been an attraction the club builders that create MOI, Moment of Inertia, matched sets.

The technical discussion, measurements and testing results are available only to registered readers

This is a great step forward in iron shaft technology. Keep it coming, True Temper, the club building community has waited a long time for a set of iron shafts like this!

EI Measurement Refined

Adjusting 3 Point Bend Measurements for Tube Deformation

By Russ Ryden, Fit2Score, A Dallas Fort Worth Club Fitter & Club Maker
The Golf Center at the Highlands, Carrollton Texas

EI profiling is one of several methods used by shaft designers and club fitters to understand a golf shaft. In several research papers on golf shafts, 3 point EI bend testing is faulted for failing to account for tube deformation under load. With the assistance and coaching from Dave Tutelman I began a study of shaft deformation in a 3 point bending test. That study, which lasted over a year, is now complete. I have developed a simple measuring process to compensate for tube deformation in 3 point EI measurements.

These illustrations show a cross section of the shaft measuring process and graphically illustrates the deformation issue.

Understand EI Deformation 1Figure 1:  The typical 3 point measuring system uses a gauge positioned at the top of the shaft. A preload is applied to the shaft, and the measuring gauge is set to zero.

This set of drawings is vastly exaggerated to illustrate the point. In fact the deformation of the shaft is a very small percentage of the bending of the shaft.

 


Understand_EI_Deformation 2Figure 2:
 When load is applied to the shaft, It bends. Golf shafts are hollow tubes, not only do they bend, they also deform, becoming oval. Deformation is a function of the hoop strength of the shaft. In linear bend testing, the oval deformation is a source of error. We want to measure the bending of the centerline of the shaft shown here as 10 units. We actually measure both ovaling and bending.

 

 

Understand_EI_Deformation 3Figure 3:  Remember, In these drawings, the ovalization of the shaft is vastly exaggerated. The top to bottom dimension of the loaded shaft changes by 40 units. Part of that dimension, 30 units is the deformation of the shaft. Not the bending of the shaft.

 

Understand_EI_Deformation 4Figure 4:  The correction; measure both the top wall and the bottom wall of the shaft to calculate how much the shaft deformed. Subtract half of that difference from the top wall measurement. In this exaggerated illustration, the actual centerline deflection is 10 units. That is determined by subtracting half the difference between the top and bottom wall deflection from the top wall deflection.

This deformation occurs in three places, the left support, the center press and the right support. To accurately determine the centerline EI, all three deformations must me measured and accounted for in the calculation of EI.Understand EI Deformation 5

Figure 5:  This is an EI instrument built for researching and understanding tube deformation during 3 point loading. A gauge under the shaft measures deformation at the bottom wall. The difference between the top and bottom gauge is ovalization of the shaft. A third gauge measures deformation at the beam support. After studying many shafts, we can now forecast deformation from hoop stiffness alone. 

ActualDeformationAdjustmentThe ovalizing of the shaft shown above is exaggerated for the purpose of the illustration. In fact it is typically less that 2% near the tip and as much as 20% near the butt. The correction does not change the shape of the EI graphics. It does modify the slope. The butt section of shafts is revealed as stiffer than uncorrected top wall deformation data. As you can see here, the subtle stiffness changes shown in inch by inch 3 point profiling are apparent in both the uncorrected and adjusted graphics. Those stiffness bumps that are the essence of feel and performance are apparent in both graphics. The adjusted graphics make butt stiffness more accurate going forward.

The three gauge instrument shown above is time consuming to use. It is now available for purchase. We knew at the onset of this research project that deformation was going to correlate to the hoop strength measurements we are already taking with a single gauge instrument.

HoopDeformationAdjustmentApplying a multiplier to the hoop deformation we have been measuring, we correct the EI data. In this illustration you can barely see a difference between the 4 point measured deformation and the 1 point + hoop adjusted deformation. The measured deformation is done at both the tip and butt supports and the press. The hoop deformation is done under the press, applying the load to the shaft while it is firmly supported on a block of metal.

A great number of shafts with different materials have been run through the 4 point measurement process. A universal correction factor has been shown to apply universally to all shafts we have tested. Hoop deformation against a solid block is a method that accurately corrects top wall measurement to center line bending. This should forever end the critique of the accuracy of 3 point measurement of golf shafts. I am indebted to my friend Dave Tutelman for his guidance and assistance as we worked on this project for over a year.

 

Golf Shaft Review KBS Tour 105 TaylorMade Stock

KBS Tour 105 TaylorMade Stock Iron Shaft

By Russ Ryden, A Golf Digest America’s 100 Best Clubfitter
Fit2Score, Dallas Fort Worth, Texas

KBS105_Image
Many of you have probably seen a KBS Tour 105 shaft in stock TaylorMade RSi 1 and RSi2 irons. As of the date this review was published this shaft is not available in the USA after market, the review samples were shipped from the KBS factory in Taiwan.

ParallelvsTaperTipIllustrationThe KBS Tour 105 used in the TaylorMade RSi’s are parallel shafts. A taper version will soon be available to club makers in the USA. For those that are not club makers and are not familiar with the terms parallel and taper let me explain. This illustrations shows the bore in the hosel of a club head. Some heads, like the RSi1 and RSi2 have parallel bores. The hole in which the shaft is inserted has parallel sides. They are typically 0.370″ diameter. They are designed for parallel tip shafts. Heads designed for constant weight taper tip shafts have a tapered bore. The bottom of the hole is 0.355″ diameter and slowly increases in diameter.

Taper tip shafts are sold in sets. Each shaft in the set is specifically designed for a particular iron, 3i, 4i, 5i, etc. The shaft lengths in the set are in 1/2″ increments and typically weigh the same despite being different lengths. The stiffness of the shafts is set by the designer. The shafts are butt trimmed by the club maker to get to the lengths needed for you set. Parallel shafts are sold individually, one length for the entire set. They are tip trimmed by the club maker to create stiffness for the different irons then butt trimmed to create the lengths needed for the set. Because they are trimmed from both ends, the shaft weight gets lighter as it gets shorter.

The balance of sets made with constant weight tapers and parallels is different. You should not attach a value judgement to that fact. But you should realize that if you are accustomed to the balance of one design, changing designs will affect your game despite the fact that the swing weights will be the same. If you want to learn more about this it is explained in greater depth in the technical article, Parallel and Constant Weight Iron Shafts.

Now that you have a basic understanding of Parallel shafts, lets take a look at the KBS Tour 105 parallels.

The technical discussion, measurements and testing results are available only to registered readers

The after market addition to the KBS Tour line of shafts, the 105 constant weight tapers is coming soon. Stay tuned, 105 grams is a great weight and will be a great compliment to the CTaper light in a fitting system matrix of shafts.