Monthly Archives: January 2014

Golf Shaft Deflection

Modeling Static Load Deflection

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

Understanding the differences in golf shafts has never been easy. Bending is the product of the elastic modulus E and the area moment of inertia I of the beam cross section at a point on the beam. The formula looks like this:

w is the bending of the beam, x is the location and k is the curvature. This is the fundamental science used by all golf shaft designers of significance. It makes simple sense to use the same system to understand their designs.

Working with my friend and technical mentor, Dave Tutelman, I added deflection modeling to my shaft knowledge base. Deflection can be calculated from EI. Knowing the EI of 36 sections of a driver shaft, a composite bend can be modeled with weight as a variable. This illustrations shows the EI profile of two shafts on the left. On the right the shafts are loaded with different weights to model their deflection when loaded.

I picked these two shafts to illustrate the value of knowing the EI profile of golf shafts. These two shafts are both rated by their respective manufacturers as S flex. The EI profile shows the butt and tip stiffness to be about the same. And yet, they show very different bend patterns when loaded as shown on the right.

The loading illustration is what you would see if you used a deflection board. I borrowed this image of a deflection board from GolfWorks.This is a classic tool used by club makers to understand shaft bending properties and to rate stiffness.

Frequency instruments have replaced this instrument in most club makers shops. Frequency gauges give the club maker a number which many software systems translate into stiffness. What is not seen on frequency instruments is the bend profile seen on a deflection board. The shortcoming of deflection boards is that they do not quantify the bend profile, leaving the club maker to compare bend properties with tracings.

Using EI values along the shaft, the deflection profile can be calculated and quantified as shown. This lets shaft engineers translate the matrix of material properties used in the shaft, wall thickness, wall diameter and taper rate into computer simulated bend properties of a golf shaft. All major shaft design companies have created software to model their ideas before they develop prototype shafts.

My EI instrument brings the shafts we play with back into modeling. The club fitter, equipped with EI measurements, understands the bend properties of the shafts he fit with. That understanding is why it was necessary to invent my own instrument and system for measuring golf shafts. The fitters that are authors on this site understand the golf shafts they fit with from this perspective.

The load applied during a golf swing is transformed into shaft deflection. That deflection is what you feel as stiffness when you swing. Feel feedback helps you time your swing. The EI bend profile determines not only the amount of deflection but also the shape of the deflection. And that shape influences how your swing/shaft interaction presents the club head to the ball at impact.

Aldila RIP Alpha Hybrid Golf Shaft Review

Aldila RIP Alpha Hybrid

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


This is not a new shaft from Aldila, it was released several years ago. It was the pioneering release of Reverse Interlaminar Placement in Aldila shafts. It has been used in all subsequent shafts. It has never been clear to me exactly what was done. Their illustrations show bias plies at both the inner and outer wraps of the shaft. Most premium shafts over the last few years have adapted to some variation of this layup design.

What brought the RIP to my attention was the release of the KBS Tour V and the Nippon Modus3 Tour 130 designs. Both have a long stable butt and mid with a rapid loss of stiffness toward the tip in the high tip section of the shaft. When working on my Hybrid fitting system I saw this pattern in the RIP Alpha Hybrid.

AldilaRIPHybridEiDfTbI secured a few more review samples from Aldila and took a hard look at the model. It has really low tip torque numbers and excellent radial consistency. If you are familiar with the table from other reviews you will notice that the format of the balance column has changed. It is now expressed in terms of the midpoint of the shaft. A positive number indicates the balance is above the midpoint, a negative number below the midpoint. This makes it easier to see the amount of counterbalance build into a shaft. What we see in the Alpha is a ‘balanced’ shaft.


In future reviews you will see deflection profiles The EI profiles I have been using may cause some confusion and consternation when looking at the charts. You can see unusual peaks and valleys is many designs. This is not how the shaft bends. That is how the designer tailored the stiffness of the shaft to create a bend profile. In this illustration you can see increasing and decreasing load applied to the EI numbers and watch how the shaft bends in response to loading and unloading.

The Aldila RIP Hybrid shaft profile, what one shaft company tour rep explained as convex vs concave when discussing two popular models, is seeing a lot of play recently. I found an example of two shafts with similar butt and tip stiffness and in my new bend modeling software applied increasing tip loads to the shafts to help me envision how these two extremes compare to each other. LoadingAnamation
This is new methodology, I am not aware of any other software implementation of load modeling based on EI profiles. What we clearly see here is the mid shaft stiffness creating a propensity for a lower launch. What you also see is the importance of matching the load you apply to a shaft. Shafts that are too stiff for you barely bend, giving you a boardy feeling. Shafts that are too soft, bend too much. As they recover from applied load during the reduced acceleration that happens just before impact, they add too much variation to head speed and orientation. That is why being properly fit into a shaft is a huge factor in shot dispersion.

When warm weather returns to Dallas we will get to reaction from the local golf professionals comparing the feel of these two designs.