Effects of Shaft Features

Flex
There's a whole separate chapter on this; check it out!

Kick point, bend point, flex point

The "kick point", "bend point", or "flex point" of a shaft, is a measure of whether the bending tendency is higher or lower on the shaft. They are not merely different names; there are at least two ways of measuring them, one usually attributed to kick point and the other to bend point.

These points are said to affect:

  • Feel: Shafts with a high kick point feel more "one piece" than shafts with low kick points, at least for golfers sensitive enough to feel the difference. Shafts with a low kick point are more "tip-flexible" and feel that way.
  • Trajectory: The position of the kick point makes a difference in the trajectory of the ball, though not a large one. In general, the lower the kick point, the higher the trajectory. There is still much debate whether this is even true, so let me conclude this section with a discussion of the pros and cons of affecting trajectory with kick point.

This was considered a very interesting parameter until the early 2000s. It is a lot less so today. In the first place, actual measurement shows a very small range for the kick point (or, for that matter, bend point) range. It varies only an inch or two over the collection of shafts measured, in the studies I am familiar with. So it really isn't a very good measure of trajectory. Russ Ryden's work on EI profiles is starting to tell us a lot more about what to look for in a shaft -- and it involves the whole shaft's flex profile, not just a single, easily measured number to represent the shaft.

Length
There's a whole separate chapter on this; check it out!


Material

During the 1920s and '30s, shafts evolved from wood (mostly hickory) to steel. They probably picked up a little weight in the process, but the results were much more repeatable and predictable, and the torsional rigidity of steel was much greater. Steel remains the predominant shaft today, but that was challenged in the '80s and '90s by composites of strong fibers laminated in epoxy resin. The most common of these fibers for golf clubs is carbon (usually but incorrectly referredto as "graphite"), though boron, kevlar, and glass fibers are also on the market. The "exotic" fibers are usually an additive to a mostly-graphite shaft.

Until the mid-'90s, composite shafts were a distinct throwback to the beginning of the twentieth century. The graphite shafts were lighter, but less reproducible and given to low torsional rigidity. Recently, graphite shafts have tighter specs on everything, and torsion characteristics may even be comparable to steel; but that comes at a price in dollars and/or weight. However, there are in-between shafts -- not challenging specs and tight tolerances perhaps, but reasonable specs and tolerances -- that are affordable.

It's worth listing some of the special characteristics of composite shafts, so the club designer can decide when they're useful and when they're simply a mark of conspicuous consumption:

Price:
It was possible to generalize about shaft price when this was first written in 1998. There is a lot more variety in the market today (2017). Prices are being pushed up -- sometimes way up -- by selling some shafts as "boutique" or high-performance shafts. At the same time, manufacturers have learned to build reasonable quality into graphite shafts, so there are competent consumer-grade shafts for rather reasonable prices. So the only generalizations I'm willing to make about price is that there is a huge range of prices for both steel and graphte (more for graphite), and considerable overlap of prices between graphite and steel. Here are a few points for comparison. Prices are approximate, and depend on where you buy them.
    • Steel
      • TrueTemper Dynalite and TT Lite: $10-$15.
      • TrueTemper Dynamic Gold: $20-$30.
      • KBS S-Taper: $55.
    • Graphite
      • Component house brands: $10-$25.
      • Name brand general market shafts: $30-$80.
      • Premium and "boutique" shafts: up to $300 and occasionally more.
Strength:
I've collected enough informal data (no, not a controlled experiment, but anecdotal) to convince me that steel shafts are more durable than graphite over the first 10-15 years of life. There isn't much data on graphite for longer periods, so we don't know any of its long-term failure mechanisms. Steel rusts over time, but seldom fails due to rust in the first 10-15 years unless left exposed to the elements..

Graphite is simply weaker than steel when subjected to concentrated shock.

  • Graphite, but not steel, shafts have failed, especially in short-hosel drivers. (This has been ameliorated in some models of graphite shaft by beefing up the tip. But that has reduced graphite's advantage in keeping swingweight down.)
  • Graphite, but not steel, shafts require coning (and sometimes ferrules) to ward off premature failure in any installation.

Weight:
Where light weight is desirable in a shaft, graphite can supply it. The lightest graphite shafts are less than half the weight of the heaviest steel shafts. Remember that a saving of about six grams of shaft weight is a reduction of one swingweight point. Thus moving from a "typical" steel shaft (at 120g) to a "typical" graphite shaft (at 70g) will save 8 swingweight points. This is worth more than an inch of extra length (close to an inch and a half) for the same swingweight.

The way to use graphite's lower weight for improved performance is to either:

  • Use it to make a longer club at the same swingweight or MOI.
  • Use it to make a club with a lower swingweight or MOI.
Both of these assume you can control the resulting club, which may or may not be a good assumption. If you can handle the extra length, or if you can handle the reduced inertial resistance, then the result will be more distance.

But the biggest advantage of reduced weight, especially in clubs other than a driver, is not the performance for any single shot. Rather, it is the golfer's own improved performance due to not being as fatigued late in the round. Carrying or pushing a heavy bag, or even just swinging heavy clubs, can hurt a golfer's ability to perform late on the back nine.

Vibration damping:
Graphite shafts cut the high-frequency vibrations of the impact between clubhead and ball, whereas steel transmits them to the hands. Thus graphites feel less harsh. This may be an expensive luxury for some golfers, but can be a necessity if:
  • You have a medical condition that is aggravated by shock, such as arthritis in the hands or arms.
  • You hit 300 practice balls a day, as the pros do.

It is conventional wisdom among golfers that the vibration-damping of graphite prevents or alleviates shock-related or repetitive-motion injuries. I have seen no medical study to confirm this, so I can't endorse that position. But there is certainly plenty of anecdotal data to support it.
Arbitrary design characteristics:
The fabrication process for composite shafts allows the possibility of building in characteristics that you couldn't in steel (at least not without some costly fabrication problems). As a result, we have a few examples of shafts with novel specs:
  • The "Nitro Flex", a very whippy shaft that still has good torsional resistance.
  • A variety of "tip-heavy" shafts, for those who want the vibration damping of graphite, but don't want the weight reduction.
  • A few extremely whippy shafts (more flexible and lighter than can be made reliably in steel) for very slow swingers. A prime example is the FiberSpeed shaft, a composite shaft where the fiber is glass, not graphite.
When this chapter was written in 1998, this advantage of graphite was more theoretical than real; there weren't many shafts out there whose desirable characteristics (except for weight and vibration damping) couldn't be duplicated in steel. But in 2017, shaft designers are using composites to tailor the bend profile, torque, and even resistance to ovaling (incorrectly referred to as "hoop strength" in the shaft industry), in ways that would be impossible in steel.

Before we leave the subject of graphite shafts, it's worth mentioning a few myths about them, and explaining the reality: A lot of people assume that graphite shafts have more "whip" (whatever that means) than steel shafts. This assumption leads to an assumption that graphite-shafted clubs will hit further than steel.
  • The first assumption (more whip) is simply not true. Graphite shafts tend to cover a similar range of flexes as steel shafts of the same nominal flex grade. Admittedly, it is possible to build graphite shafts softer or stiffer than steel. But this is only an issue if you need something stiffer than a Rifle FCM 7.5, or something softer than a True Temper Release "L". There aren't many golfers whose proper shaft is outside these extremes. For the rest of the world, there's nothing magic about the flex of graphite.
  • The second (more distance), where it is true at all, is a consequence of the lower weight of graphite, seldom its flex characteristics.

Torque
When discussing shafts, "torque" refers to the ability of the shaft to resist a twisting force about its centerline. Actually, the technical term "torque" really refers to the twisting moment itself, as we saw in the section on physical principles. The proper measurement of torque would be to measure the twisting moment, in some unit like foot-pounds or gram-inches. But for shafts, the measurement is degrees of twist for a given applied torque. A high torque rating paradoxically means that the club is low in resisting twist. It really isn't high in torque; quite the opposite, it is high in "torsional deflection".

I said a "given" applied torqe, not "standard". There is in fact a standard torque for this measurement: one foot-pound. But the test really isn't quite standard because the clamps at each end (applying the foot-pound of torque) and the unclamped length to be measured are not standardized.

Torque can be, and often is, significantly different for steel and graphite:

  • Steel shafts are pretty stiff in resisting torque, and there is little to choose among them. The typical steel shaft will have 2.5-3.0 degrees of torque for "wood" shafts and 1.7-2.0 degrees for "iron" shafts.
  • Graphite shafts are naturally flexy in torsion. Low-priced graphite shafts are generally over 4 degrees, and as high as 7 degrees. In order to compete with steel in twisting rigidity, the manufacturer must do something special. That usually results in a substantial increase in weight (sometimes to the point of similarity with steel) or a substantial increase in price. Typically, the fix is some of each: weight and price. Layers of carbon fiber are added to the shaft, with the fibers oriented on a 45 bias; that direction provides maximum resistance to torque. The extra layers add weight and cost.

Under the dynamic forces of the swing, the clubhead will twist through the ball, just as the shaft whips through the ball in flex. This means that there is a second dimension to worry whether it's at the proper point in the load-unload cycle when the clubhead meets the ball. There are several schools of dealing with this, to whit:

  • Consider torsional flexibility to be a degradation to be minimized. This is my preferred approach. I would buy the shaft with the right flex and the stiffest torque I could afford. (Of course, this isn't an issue with steel. But if you need graphite, it becomes a serious economic consideration.)

    This solution comes with a price. Reducing torsion turns out to make the shaft feel a lot stiffer, even if the actual flex is not affected. Which brings us to...

  • Trade off torsional stiffness against shaft flex to give an overall "feel". For instance, consider two shafts "A" and "B". "A" is "looser" in torque than "B", but is enough stiffer in flex that it matches the same golfer.

    What is the "currency" of the trade? According to Summitt and Wishon, frequency (a measure of shaft flex) trades against the fifth root of torque. For example, a 5% increase in torque can be countered by making the shaft stiffer to the tune of a 1% increase in frequency. Unfortunately, the relationship doesn't stay linear over a very wide range. For instance, many budget and mid-priced graphite shafts have a torque twice that of a comparable steel shaft. Using the fifth-root trade, a steel shaft would have to be 15% softer (measured in frequency) than the graphite shaft. A 15% frequency difference corresponds to the difference between an X-flex and an L-flex for shafts rated on the FCM scale.

    I report this approach because it is the conclusion of the authors of a widely-respected study of shafts. However, I have a lot of trouble buying it. I can believe that the tradeoff could result in a constant feel, but doubt that it would provide constant performance. Consider:

    • The essence of flex matching is to unload the shaft at the right point in the golfer's swing.
    • If "torque matching" has any validity at all, its essence should be, similarly, to unload the rotational energy in the shaft at the right point in the swing.
    • But the notion of a trade denies these essences; it trades degree of unloading in one axis for unloading in another. Using the trade, the direction of the clubface at impact would be dependent on where you were on the trade curve. That's not what shaft matching is about.
  • Find the ideal torque for the golfer's swing, so the head is exactly square at impact. This is analogous to choosing the flex, and is arguably the only correct way to do it. However, nobody does it this way, and it's safe to say that nobody really knows how to do it systematically.

My conclusion about torque? If money is no object, go ahead; make Aldila's day and get low-torsion graphite. But be aware that most inexpensive graphite shafts are not low-torsion.

If money is a consideration, here's my personal strategy:

  • For the driver, decide what length and swingweight you want. If the result calls for a lighter weight shaft than steel can provide (and it almost certainly will), get graphite in the torsional stiffness your swing needs.
  • For the irons, it is more likely that steel will be the preferred material; many stronger golfers actually need the extra weight to regulate their swings. But there will still be plenty of golfers who want the lighter weight or vibration damping of graphite. For them, either pay for tighter torque or determine what they really need. It may be OK with garden-variety graphite, since an iron head has much less moment of inertia than a driver head, and thus requires less torque to square it up.
Weight
As with torsion, you pay for low weight. You may pay for it in dollars, or it may be in torque. As the weight decreases, the hardest spec to maintain is torque. So you may have to strike a happy medium in specs or dollars.  My strategy here is the same as with torsion; for the majority of your clubs,

For a driver, especially an over-length one, do what you need to do.


Last modified May 15, 2017