Measuring the Golfer for Flex

Obviously, we need to estimate for each golfer how much his/her swing loads the shaft and how fast it unloads. There are two fundamental determinants of this:
  • The primary determinant is clubhead speed.
  • The secondary determinant is clubhead acceleration.
That is, you can make a good rough determination of the best shaft flex just from knowing the golfer's clubhead speed at impact. If you know how that clubhead reached that speed, you might want to "fine tune" the recommended flex. If the clubhead speed is reached with a "hitter's" swing (like Nick Price, a short, quick downswing), then a stiffer shaft is called for than a "swinger's" swing (like Freddy Couples, a long, slow-tempo downswing). Since both can achieve the same clubhead speed at impact, an estimate of acceleration can be a useful adjunct to shaft selection.

Of course, the best "estimate" comes from a direct measurement of clubhead speed and acceleration. Meters do exist for both:

  • There are quite a few electronic "swing analyzers" that provide at least the clubhead speed at the bottom of the swing.
  • True Temper now makes a device called "The Determinator", which measures the load on the shaft. This is supposed to combine clubhead speed and acceleration to give the proper shaft stiffness for a swing.
For those whose budget precludes these instruments, there are ways of estimating both quantities.

Driver carry distance:
This is the most common clubhead speed estimator. The GolfWorks catalog suggests the following table:

Driver carry distance (yds)130155180205225250
Driver clubhead speed (mph)5060708090100

This is fine as long as you can get a realistic estimate. Serious workers in the field have concluded that the vast majority of golfers overestimate their "average" distance, probably due to equal mixtures of ego and "selective memory". My experience concurs, including my estimates of my own distance.

I recently played a round with a golfer who was using S400 Dynamic Gold shafts (a rather stiff shaft). Judging from the way his shots behaved, the clubs were much too stiff for him. When I inquired at the end of the round how he arrived at those shafts, he told me, "I normally hit a 3-wood 260 yards. I was off my game today." Having seen his swing, I don't doubt that he hits an occasional 260-yard 3-wood -- once a season with a following wind. But he's confusing those occasional hits with his "average", a mistake that has saddled him with clubs that fit him very poorly.

5-Iron carry distance:
A table comparable to the table for driver distance is:

5-iron carry distance (yds)85105120140160180
Driver clubhead speed (mph)5060708090100

Yes, I did intend that to be driver clubhead speed versus 5-iron carry distance. The tables that follow are based on driver clubhead speed, so that's what we'll be trying to estimate. A more accurate fitting method would be to actually measure both the driver swing speed and the 5-iron swing speed, since some golfers have different swings for woods (especially drivers) and irons. The simplified tables in these notes don't take that into account. But you can allow for it. Use the "driver carry" table to estimate clubhead speed for the purpose of specifying shafts for the woods. Use the "5-iron carry" table to estimate driver clubhead speed for the purpose of specifying shafts for the irons.

150-Yard club:
This is a variant of the "5-iron carry" table, suggested in the Golfsmith catalog.

150-Yard club3I4I5I/6I6I/7I8I/9I
Driver clubhead speed (mph)<7070-8580-9590-105105+

Downswing stopwatch:
Now we're into methods for estimating acceleration. Golf Digest (November 1994) had an article by Ed Weathers suggesting timing the golfer's downswing with a stopwatch. The shorter this time is for a given clubhead speed, the greater the acceleration.

Practice timing the downswing until you can get consistently similar readings for any single golfer. According to Weathers, these times will be from 0.25 seconds (very high acceleration) to .65 seconds (low acceleration). You can use these results to modulate the shaft recommendations resulting from clubhead speed.

The 1995 Golfsmith catalog also suggests this method of estimating acceleration, assuming that they can't sell you a $100 Determinator.

Swing keys:
Sometimes you can tell just by looking at certain features of a golfer's swing whether they load the shaft with a lot of acceleration. Assuming you have an "instructor's eye" for the swing:
  • Note the shoulder turn. If it's more than 90 degrees, it won't take a lot of acceleration to get good clubhead speed; the swing is long enough to get there gradually. But a good clubhead speed with a shoulder turn of less than 90 degrees suggests a high load on the shaft. (For you doubters of this method, John Daly uses a softer shaft than you'd guess from his length. His power comes from a huge shoulder turn, not strength leading to acceleration.)
  • Note the beginning of the downswing. A "pull the cord" initiation of the downswing results in less early loading of the shaft than a "hit it with both hands" initiation.

Last modified Dec 1, 1998