Assigning a Grade of Flex
The Standard Flex Grades
There are five "standard" grades of flex. From the most flexible to the
stiffest, they are: L, A, R, S, and X. Informally, what these grades mean
|L||Ladies||For women or high handicap|
|A||Flexible||For seniors or high handicap|
|R||Regular||For the average player|
|S||Stiff||For low handicap|
|X||Extra-stiff||For scratch player|
This table is constructed from words in the Golfsmith and GolfWorks catalogs.
But they should really refer to swing speed and strength, not gender, age, or
The reason I put "standard" in quotes is that, while the names are industry
de-facto standards, there is no standard measurement of the stiffness
represented by each of the grades. Yes, that means that one company's "R"
flex may be stiffer than another's "S" flex. In fact, there are cases that
approach this between two shaft models from the same company; measurements
show the True Temper Dynamic Lite "R" shafts for irons to be stiffer than the
True Temper Gold Plus "S" shafts.
Nevertheless, until the industry agrees on flex standards or we all buy
Dynacraft's DSFI book (which publishes detailed measurements for most of the
shafts available), the standard flex grades are all we have. So let's pretend
they are truly standard and continue.
The reference catalogs (Golfsmith and GolfWorks) have a number of tables that
suggest measurement to determine flex for a given golfer. Here are some
|150-yard club (1)||8-9||6-7||5-6||4||3 or more|
|5-Iron carry in the air (2)||>175||146-175||116-145||90-115||<90|
(1) Golfsmith catalog.
|Driver carry in the air (2)||>245||211-245||171-210||135-170||<135|
(2) GolfWorks catalog
We should recognize this as the tables we used to estimate clubhead speed
"translated" into recommended flex. I think this is easier to see
graphically, so I've reproduced the tables as graphs.
Shaft Flex vs. Clubhead Speed
Speed MPH 0 0 0 0 0 0 1
Shaft Flex vs. 5-Iron Carry Distance
Carry Yds 0 0 2 4 6 8
0 0 0 0 0
* Golfsmith numbers estimated from recommendations for 150-yard club.
Note that GolfWorks tends to recommend a somewhat stiffer shaft than does
Golfsmith, for the same golfer characteristics. I can think of a couple of
Before I give this a rest, let me point out that the Golfsmith book "Golf
Clubs - Design and Repair" includes the passages:
- Ralph Maltby of GolfWorks and Carl Paul of Golfsmith are experienced and
opinionated on all facets of club design and construction. That doesn't
mean they always reach the same conclusion. In this case they don't.
- Following in this vein, perhaps the experts disagree on whether to shade
their ratings in favor of distance or accuracy. We know, within a range
of reasonably-fit shafts, a stiffer shaft will give more accuracy and
less distance than a flexible one.
- Of course, it may be that they just have different favorite shaft models,
and that those models have substantially different characteristics for
the same nominal grades.
"Studies into golf club design and playability show . . . that
under almost all circumstances, golfers will perform better with
lighter swingweights and stiffer shafts....
"Contrary to popular opinion, studies show that rather than
'jumping' into the ball, the softer more flexible shafts tend to
lag, leaving the clubface out of alignment with the hands and
therefore promoting misdirected hits. Stiffer shafts, on the other
hand, tend to better maintain the relationship between clubface and
hands through impact, and therefore provide straighter shots."
The "lighter swingweights" advice from Golfsmith should not be surprising by
now, but the "stiffer shafts" seems to contradict the fact that their charts
recommend LESS stiff shafts than GolfWorks. However, I think GolfWorks takes
shaft stiffness to the extreme, possibly pandering to the macho who wants to
say, "I need a stiff shaft 'cause I hit it so hard." I've seen other articles
by knowledgeable pros who say most people use TOO stiff a shaft.
The latter point of view has become much more mainstream lately. In fact, a
number of the most popular OEM clubs are going to softer flexes without
changing the nominal designation (e.g.- "R" or "S"). The idea is to improve
the players' performance without trashing the players' ego.
Let me cite my own experience. On the GolfWorks chart, I'm a definite "S". On
the Golfsmith chart, I'm between an "R" and an "S". From a fair amount of
experimentation, I consistently hit better with an "R" than an "S". Moreover,
the best results for my own swing come when I custom tip-trim a shaft to
somewhere between an "R" and an "S". So I know which chart I believe.
You pays your money you and takes your choice.
Other Flex Grades: Frequency
If simple letter grades aren't well standardized, then how about going to an
objective measurement and grading the shaft with the measured numerical
value? Most people who are making serious flex-standard proposals are
recommending the use of the frequency of vibration as the number to designate
This is a good idea, but requires overcoming a few problems. The most
significant is that frequency depends not only on stiffness but also on
length (longer shafts vibrate more slowly) and weight (more weight for the
same stiffness causes slower vibration). When Dynacraft and Apollo jointly
did the study that resulted in "The Modern Guide to Shaft Fitting", they
standardized on length and weight. They cut the shafts to a standard length
and swingweighted the clubs consistently to make the measurement.
|Men's driver shafts||43" club length||Swingweighted to D1|
|Men's iron shaft||37.5" club length||Swingweighted to D1|
|Ladies' driver shafts||42" club length||Swingweighted to C6|
|Ladies' iron shafts||36.5" club length||Swingweighted to C6|
As a result, the annual Dynacraft DSFI "Shaft Fitting Addendum" is the most
objective comparative measurement of shaft flex available.
Later in this section, we'll see that some manufacturers
(specifically Royal Precision, which was originally Brunswick)
grade their shafts by frequency. Now some small, high-quality graphite
shaft makers (e.g.- Apache and Composites Dynamics)
are also beginning to specify target frequency for the club.
Other Flex Grades: DSFI and RSSR
Dynacraft and GolfSmith, the two biggest component vendors, each rate the
shafts they sell (from all shaft manufacturers) according to their own
proprietary ratings: Dynacraft Shaft Fitting Index (DSFI) and Recommended
Swing Speed Range (RSSR).
DSFI is the result of a huge study by Dynacraft and Apollo, related in the
book by Summitt and Wishon mentioned earlier. They took 400 driver shafts and
a similar number of 5-iron shafts, and:
As a result of the golfers' reactions, they rank-ordered the shafts by
"effective stiffness"; that is, what the golfers felt the stiffness was. This
correlated well with a separate rank-ordering based on clubhead speed for a
- Measured all their objective characteristics.
- Got experimental, subjective reactions to them from real golfers.
- From high-speed pictures of golfers' swings, found the speed at which the
shaft was JUST straight; that is, the maximum-accuracy speed for the
shaft. (This was done for only a few of the shafts.)
Then they came up with a mathematical formula for predicting, from the
measurements, the observed rank ordering. They applied to that formula a few
correction factors, and it also gave a good approximation to the clubhead
speed for a straight shaft. They called the formula the Dynacraft Shaft
Fitting Index, because it promised to give a single number that would fit a
shaft to any golfer's clubhead speed.
The most important elements of the DSFI are frequency and torque. In fact,
DSFI is directly proportional to frequency divided by the fifth root of the
torque. (That is, the longitudinal stiffness of the shaft is much more
important than the torsional stiffness, but the torsional stiffness does
contribute something to the feel of the shaft.)
Dynacraft annually publishes a book of shaft measurements for most
commercially available shafts. The 1995 version rates over 1200 shafts. In
addition to the DSFI, the "Annual Shaft Fitting Addendum" gives data such as
frequency, actual cut weight, and measured torque (manufacturers' specs tend
to list a stiffer torque than is factual). I find it an important tool in my
When Wishon left Dynacraft to become Golfsmith's chief technical officer,
Golfsmith immediately began publishing a spec they call RSSR in their
catalog. This is a range of clubhead speeds for which the shaft is
presumably appropriate, such as "70 mph - 80 mph".
My own experience with RSSR has been so bad that I'll continue to buy the
Dynacraft DSFI book rather than put any credence whatsoever in Golfsmith's
free data. Early this year, I made up a trial 5-iron with a Brunswick Rifle
shaft. Knowing that my favorite True Temper shaft is a Dynamic Lite, trimmed
to be somewhat stiffer than "R", I wanted to find out which Rifle was the
most similar to it. The DSFI rating for the Rifle was not yet available, so I
looked at the RSSR. Here are the ratings (both RSSR and, now that I know it,
the probable DSFI and frequency):
|Dynamic Lite "R"||70-80||78||307|
|Dynamic Lite "S"||80-90||85||326|
From the RSSR, I decided that the Rifle "6.5" would be the best match my
favorite Dynamic Lite. The DSFI and frequency numbers, however, strongly
indicate the Rifle "5.5". Sure enough, the 6.5 club turned out to be the
stiffest, harshest iron that I or any of my friends had ever hit. And the
price of that one wrong shaft would pay for a year and a half of the DSFI
Other Flex Grades: True Temper Letter-Number
True Temper offers some of their shafts (generally those with "Gold" in their
name) in a finer gradation than the five basic ones. Under this system, the
middle of the basic grade is designated "300". Thus a middle "S" shaft is an
"S300"; a somewhat stiffer "S" might be an "S400". The subgrades go from
"100" to "500".
True Temper charges about 50% more for this tighter spec, which is the only
difference between the Dynamic Gold and the Dynamic, or between the Dynalite
Gold and the Dynalite.
But wait! True Temper doesn't actually flex-match the subgrades. What they do
is manufacture a shaft to a design of, say, an "S". Then (without any flex
testing at all; they assume the shaft has indeed come out an "S"), they weigh
the shafts, and sort them by weight into slots. The heaviest become "S500",
the lightest "S100", etc. This tends to make them closer by flex than if they
had just been randomly selected from the "S" output. However, measurements
show that this does not assure a monotonic flex progression nor a real flex
match, just a good weight match. But several catalogs still refer to them,
erroneously, as "frequency matched."
Other Flex Grades: Brunswick Frequency Coefficient Matching (FCM)
Brunswick (later FM Precision and now Royal Precision)
is the only shaft manufacturer that grades shafts by numerical frequency
(for some shafts), instead of the usual LARSX letter grades. In the
Brunswick system, a shaft oscillation of 255 cycles per minute for a 43" driver
is called a 5.5 flex, and is claimed to correspond roughly to other manufacturers'
"R" flex. (I have found Brunswick-graded shafts to play stiffer than this
advertised equivalence; but it's a "predictable stiffer.") A full
flex grade corresponds to one "point" on their scale, or 10 cycles per minute
of oscillation; thus an "S" grade from another manufacturer would be
Brunswick's 6.5 (265 cycles per minute).
Because the flex grades are derived by frequency matching, Brunswick claims
that a set of their shafts is matched better than their competitors' within a
matched set of shafts. They do charge for the matching. The shafts go for
about $12 apiece, comparable to the most expensive steel shafts available. In
other high-priced steel shafts, you're paying for light weight; in the
Brunswick Precision, you're paying for flex matching.
Last modified Dec 4, 1998