Lessons from ShaftLab - 2

What TrueTemper learned

The November 1994 issue of Golf Digest contained an article (Ed Weathers, "What Flex Do You Need?") describing shaft research done by TrueTemper at their lab in Olive Branch, Miss. The research was based on a new instrument they were using to measure shaft bend dynamically. The instrument, shown in the picture which was clipped from the article, is clearly the prototype for ShaftLab.

The article put forth a number of findings, based on measuring many golfers' swings with the prototype instrument. Here are the lessons Weathers reported -- and some other stuff from reading between the lines and having played a little with ShaftLab.


(1) The three profiles

All golfers' swings fall into one of three basic shapes on the ShaftLab trace (figures courtesy of the ShaftLab web site):
Double-peak -
The most common swing, accounting for more than half of all golfers. The swing loads the shaft to start the downswing, and again with the wrist snap.
Single-peak -
Typically hard swingers with quick swings, who load the shaft for the whole downswing.
Ramp -
Smooth swingers with longer, slower swings, who often don't bend the shaft a lot to get their clubhead speed.

(2) Clubhead speed is not a reliable indicator of how much you bend the shaft.

The length and style of your swing has at least as much to do with it as the eventual clubhead speed. Acceleration is probably a lot more important. If you get to your maximum clubhead speed in less time, then you are accelerating more -- and probably bending the shaft more.

In addition, the shaft bend is affected by which muscles you are using to get the clubhead moving. If you are getting clubhead speed from your body turn and just allowing the clubhead to release using "soft hands", then you probably don't bend the shaft as much as someone who uses hand and wrist action on the grip to generate clubhead speed.

(3) The biggest factor in shaft fitting is maximum bend of the shaft.

Weathers writes,
"Most of the players we tested had, over the years, come to prefer shafts that gave them between 2 and 3 inches of toe-up deflection -- a bit more for quick-hitting swingers. More than that, the theory goes, and the club is bending too much to control; less, and you don't have any feel for the club."

This implies that TrueTemper believes that shaft fitting involves choosing a flex that keeps the maximum bend within a prescribed range. And, when I looked at ShaftLab's recommendations for a variety of swings, maximum bend seemed to be the factor that correlated with the recommendation. I didn't have enough data to see whether they were changing the target range based on the time of the downswing, but they may have.

Are they correct? For the overall stiffness of the shaft, I think they are. Their theory makes as much sense as any I have seen so far, and a lot more sense than most. But... Today's shaft manufacturers using today's materials can manipulate the bend profile and weight of a shaft in ways that were just not done in 1994. These are also important fitting parameters, and ShaftLab does not address this part of shaft fitting.

(4) Changing shaft flex does not increase your clubhead speed

Weathers writes,
"Changing your shaft flex will not affect your clubhead speed... None of the players tested showed any difference in clubhead speed from shaft to shaft. If their impact speed with an X flex was 90mph, then their impact speed with an L flex was 90mph -- and the same with an R flex or an S flex."

This is confusing, because it seems to be refuted by the next thing he says.
"Kick velocity can add more than 10mph to your clubhead speed."

These two statements can be true only if (a) kick velocity is not affected by shaft flex or (b) kick velocity does not affect clubhead speed. Now (a) is inconsistent with the whole ShaftLab fitting philosophy. ShaftLab is based on the notion that a stiffer or more flexible shaft than the ShaftLab club's shaft has the effect of scaling the graph larger or smaller without changing its shape. Consider:
  • If the underlined statement is not true, then there is no basis for saying that you can scale the maximum deflection to get the proper shaft flex. That whole fitting process depends on the idea that the graph changes size but not shape with shaft flex.
  • If the underlined statement is true, then the kick velocity also scales with shaft flex. We will see why on the next page.
Basically I'm saying that if changing flex increases the maximum bend by 30%, then that same flex change should increase the kick velocity by 30%. So if kick velocity can add to clubhead speed, then changing flex has the potential to add to clubhead speed. Which brings us to (b). We will find out later that kick velocity has negligible effect on overall clubhead speed -- as counterintuitive as that might be.


Weathers cited a few other lessons, but we're going to defer them to the next page. That's because we can figure them out for ourselves, based on looking at ShaftLab data that I have available. It's always better to deduce the rule from the data; you understand and remember it better that way.


Last modified  11/07/2017