Let's suppose we bought a 48" wooden dowel. If we put one end of this dowel in a vice and hung a 5 pound weight from the
other end, the dowel would bend some amount. The bend is called shaft 'flex' in the golf
industry. If we now put a steel reinforcing bar in the vice and hung the same weight,
the rod would give a little but certainly not as much as the dowell. We would say the rod
is stiffer.
Similar to measuring swingweights, the industry has come up with a a scale of values
for measuing how much the golf shaft bends (flexes) under a given hung weight.
Unfortunately this is where the standardization story ends. What one shaft manufacturer
uses for the weight (5 pounds, 6 pounds, etc.), at what exact point they hang the weight,
at what point they vise grip the other, and how tight they tighten the vise, all have an
effect on how much the shaft will bend. Shaft manufacturers have not agreed on one
standard method to do this test. Consequently, a shaft labeled 'extra stiff' by one
manufacturer may be 'regular' using another's measuring approach. Although measurement
devices have become more precise (frequency measuring) the problem still exists. The
following categories have been in use for many years and are at least helpful guidelines
for consumers.
L = Ladies (for average women golfers, short hitters)
A = Amateur (usually for seniors and stronger women swingers, 60 mph+ swingspeeds)
R = Regular (the majority of men golfers with swing speeds around 75 mph+)
S = Stiff (for faster swingers mostly low handicappers in the 95 mph+ range)
X = eXtra stiff (for fastest swingers and pros 115 mph+)
To help determine what shaft flex you need you'll have to know your swingspeed. Swingspeed is
easily measured by a $ 20 device which is attached to your driver. Using the above table, if you found out your swingspeed
was around 80 miles per hour, then you'd need an R shaft.
Shaft flex is very important in improving club feel and shot performance. The general
rule is to specify the most flexible club you can control. Just because a stiff shaft
seems to fit the faster, longer hitter doesn't mean that you will swing it faster and
longer. If there is one area of clubfitting that makes sense it is in knowing your
clubhead speed and getting shafts which are appropriate for that speed.
Further complications
It sounds from the above flex writeup that, although there aren't any standards, there
is some semblance of sanity in using the guideline categories if you know your swingspeed.
And that's true. However, some shafts are simply labeled 'flexible', some 'firm', some
'soft'.and so forth. You'll have to ask the vendor what these terms approximately mean and
hope for the best.
In addition, a shaft doesn't only 'bend' when in motion, it also 'twists'. Think about
grabbing the dowel at each end and twisting it. The industry refers to this as shaft
torque. Some shafts twist very little, some quite a lot. It is possible to buy a shaft
that is S (stiff) with a high torque (twists a lot) that has similar feel characteristics
to an R (regular) shaft with very low torque(doesn't twist much). Gary Wishon, expert club designer,
devised a useful table relating these flex,
torque, swingspeed combinations to assist in the shaft specification process.
A few years back a device was invented to measure how quickly a swinger accelerates the
clubhead on the downswing. This too can impact the flex rating you specify for your
shafts.
And then there's frequency matching...
If you get this deep into the subject you really need to consult a knowledgable
clubbuilder for help. Suffice it to say that the broad flex categories given above are
acceptable to most golfers who don't make a living at the game. It wouldn't hurt to get
your shaft flexes measured at a shop to determine what they are. If you have a particular
club or two that feels and performs better than the others, you should probably check out
these clubs' flex (and swingweight) and match your other clubs to these specs.
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