How I fit for heft

I have found a way to fit a golfer for heft across a set. (Normally, it is a set of irons, and I'll describe it this way. But, if judiciously done, the process could be extended across the whole set.) The process here does not assume that the clubs will be MOI-matched or swingweight matched; the result may be either -- or neither. But it will give a good heft fit for that golfer, across the set.

The process applies only to clubs whose major intended use is full swings. Most golfers use their sand wedge and lob wedge mostly or only for finesse shots around the green, partial swings and punches. Those clubs need to be heft-fit separately, based on their primary use. You should not expect them to be an extended match of the rest of the set.

In the description below, I assume a swingweight scale as the "heft meter" in your shop. But the process works just as well with an MOI pendulum or MOI spring. In neither case am I assuming that the match will be an MOI match or a swingweight match; everything just works out for the best.
  1. Decide on the clubs that will be included in the match. Generally this will be full-swing irons, or perhaps include the hybrids if the shafts are about the same length, weight, and balance as the iron set -- and likewise for the grips. If not, see the end of this section for tips on how to deal with it. For the rest of this discussion, I will assume the set is irons, from the PW to the 4-iron.
  2. Find a pair of clubs corresponding to the extremes of the set, whose components are similar to the target set. In our example set, the extremes would be the 4i and the PW. (If the target set is already built, and you are just re-weighting them, that is ideal for testing.) It is important to have grips on the test clubs similar to the grips for the target set as well.
  3. Take those two clubs, the golfer, and a roll of lead tape to a measuring site. It is a lot better if it is a real grass site; driving range mats tend to mask the effect of fat hits, and avoiding fat hits are definitely part of the iron fitting process.
  4. Have the golfer hit the shortest club (in this case the PW), and adjust the heft with lead tape on the back of the clubhead or around the hosel. Adjust until the fit is best. For irons, I do not worry about maximizing distance. My indication of a good fit is reliability: the most consistency in distance and direction, and the fewest percentage of bad hits. (If your test subject is a good golfer, that will probably be his/her figure of merit as well. If you can't convince the golfer not to obsess over maximum distance, the process still works with distance as the figure of merit.)
  5. Once you have the right lead tape on the shortest club, leave it there and repeat step #4 for the longest club (in this case the 4-iron). You may want to switch back and forth between the clubs a few times, to make sure that hitting each club does not reduce the reliability of the other club. Golfers have some "swing memory", and on-the-course performance has to avoid single-club swing memory.
  6. Take the two clubs back to the shop, with the ideal lead tape still on them. Measure the swingweight (or MOI, if that is your instrument of choice).
  7. Take a piece of graph paper, and make a plot like the one below. Use the values you measured! The graph below is for my measurements.[1]
    The red dots are the fitted clubs' measured length and heft (swingweight or MOI). Draw a straight line between the red dots. Now locate the other clubs on the line, according to their lengths; for instance, the 5-iron in this set will be 38.5", so put the blue 5i dot where the curve meets the 38.5" gridline.
  8. The graph now gives the fitted swingweight of each club in the set. A few things to note, so you can understand the full flexibility of this process:
    • If your instrument measures MOI instead of swingweight, the the plot is in MOI and the graph gives the fitted MOI of each club in the set.
    • The curve shown happens to be an MOI-matched set, and it will be MOI-matched if you build to those swingweights. (How do I know? Because the swingweight slope is 1.3 points per inch.)
    • If the 4i and PW had been fitted to the same swingweight, then the line would be horizontal and the golfer would be properly fitted to a swingweight match.
    • If this golfer fits something other than a swingweight or MOI match, the process will discover the fact and give the proper match.
When I build the set, I match them without grips. They build to about 10 swingweight points higher than the gripped clubs, and they match one another better when done. If I have the opportunity to measure the red-dot clubs (the extremes that I measured) without the grips, then those measurements go on the graph.

The process assumes that the shafts and the grips are similar in weight and balance across all the clubs being matched. If this is not the case, you need to alter the process in a rather complicated way -- more complicated than I am willing to do myself. For instance, if the irons have 85g shafts, the fairway woods 80g shafts, and the driver a 65g shaft, I would use this process to match the irons and fairways, but fit the driver separately.

Altering Heft

Now we know how to estimate heft before the fact, and measure it after the fact. But a clubmaker is often faced with an important practical aspect: altering the MOI or swingweight when a design that's good for other purposes -- particularly length -- gives the wrong heft.

 Let's say you have picked the components you need, and the swingweight is just wrong. You can't go to a heavier/lighter shaft or clubhead; the reason might be as simple as you're starting with an already completed (or store-bought) club. What do you do to increase or decrease the swingweight.


Increasing heft

From the definition of swingweight, we can increase it by adding weight more than 14" from the butt or subtracting weight less than 14" from the butt. Let me strongly recommend against the latter; any swingweight change achieved near the butt is bogus, and is not reflected in a heavier-swinging club. There may be other uses for butt weight for some golfers, but swingweight adjustment is not one of them.

If you're considering heft in terms of MOI, you won't suffer any such confusion; weight at the butt has no effect.

 So we'll have to add weight to increase the heft. In order to minimize the total weight gain for a particular swingweight or MOI gain, we'll add it as far as we can from the pivot, at the clubhead. How do we do this in practice?

  • The best way is inside the clubhead, if that's physically possible. Most woods and metalwoods either have weight ports or at least have room for you to make one. A few irons also have them (including some models from Golfsmith and most from Tom Wishon). If your club has a weight port, you can increase the swingweight with lead or tungsten (discs, powder, or shot) and epoxy or "mouse glue" to hold it in place.

    If your wood doesn't have a weight port, you can make one. The technique of making a weight port is slightly different for woods and metalwoods. With woods, you just have to remove the soleplate and you can do the obvious woodworking to hollow out an area and fill it with lead and epoxy. Then replace the soleplate. (Check a repair book for the ins and outs of removing and replacing soleplates.)

    With metalwoods, drill a hole in the bottom of the hosel (or just remove the hosel plug if it's removable). Put a "paste" of lead or tungsten powder mixed with epoxy or mouse glue into the hole. Then replace the hosel plug. A couple of details:

    • You can use just the "Part A" of two-part epoxy. That way, there is no working-time problem. The "paste" stays sticky and viscous forever, so the fact that it isn't a hardened bond shouldn't hurt. The down side is that, left in a car trunk or garage, the past might flow to the lowest point. The up side is that it won't ever break loose and rattle, as a cured epoxy might.
    • When you drill the hole, use a 1/4" bit. The hole will be small enough to leave a shoulder to seat the shaft, yet big enough to fit a plastic drinking straw -- my preferred tool to insert the weighted paste.
    • If you have to make a new hosel plug, you can do so by punching it out of plastic -- like the polyethylene top of a coffee can. My tool of choice for the punch is the sharpened tip of a steel shaft of the right diameter. Sharpen it with your 20 coning countersink. Then use a [not sharpened] shaft tip to seat the plastic disc in the hosel.

  • If your clubhead doesn't have a weight port and you can't or won't add one, add the weight with lead tape on the clubhead itself. Theoretically, the best place to put the tape is somewhere that doesn't greatly affect the placement of the CG of the head. Note that this implies adding tape on two diametrically opposite sides of the clubhead, with the CG on the line connecting them. If you can do this at the heel and toe of the club, you'll also be increasing the peripheral weighting, thus making the sweet spot bigger.

    But, in truth, the position of the tape won't make too much difference. The tape will seldom be as much as 10 grams, so neither the moment of inertia nor the CG can be much affected by it. (It takes a lot of tape to get to 10 grams; the tape I use is a half-gram per inch, and that's pretty standard.)

    I have heard a number of people complain that they don't like lead tape because it's "ugly". The best I can do here is to point out relevant classic quotes: 

    • "Beauty is as beauty does." (William Shakespeare, poet.)
    • "Form follows function." (Louis Sullivan, architect.)
    • "When you hit the ball, you'll forget what it looks like." (John Solheim of Karsten Golf, describing his incredibly ugly Ping Zing.)

  • Some still are convinced by the "ugly" argument, and advocate putting weight at the tip of the shaft inside the hosel. There are two ways of accomplishing this:
    • Ready-made tip weights, that are epoxied into the shaft tip when the shaft is installed in the head. These are available in lead, brass, and tungsten.
    • Heavy powder (lead or tungsten) added down the shaft of an already-assembled club, and secured near the tip with a cork. (Of course, you'll have to remove the grip to add the powder and cork.)
    This is okay, as long as you don't add too much weight there. Weight at the shaft tip will move the CG of the clubhead (and thus the "sweet spot" of the club) upward and toward the heel. This is undesirable, but the move is negligible as long as you don't put more than about 10 grams there.

    A more serious problem with this approach is the danger of weakening the shaft tip. This could result from:

    • The flange on the bottom of ready-made shaft-tip weights forces the shaft to "bottom out" short of the bottom of the bore. That means there is less supported tip in the hosel. Most weight designs limit this to about 1/16", but some steal more bore from the shaft. "Short-shafting" is the most common cause of graphite shaft breakage.
    • The second leading cause of graphite shaft failure is an epoxy "plug" inside the shaft, that rises to or above the top of the hosel. If you epoxy the weight in place inside the shaft, it becomes such a plug. So get a weight that isn't a tight fit inside the shaft, and don't epoxy it to the shaft but rather inside the hosel, or just epoxy the flange to the tip of the shaft.
    • If you are using powder and a cork instead of epoxying in a tip weight, the cork or column of compressed powder may have the same effect as an epoxy plug.
    These failure modes are much more common in graphite shafts than steel. As Murphy's law would predict, shaft-tip weights for graphite shafts have thicker flanges and are longer, leading to more shaft vulnerability. So be careful.

  • I have seen some advocate drilling holes in the stainless steel of the clubhead, and filling the holes with lead. I don't mean a weight port to the inside of a hollow clubhead, but rather a replacement of stainless steel with lead.

    This is pretty ineffective, because the gains of replacement are pretty trivial. Stainless steel weighs 8 grams per cc, and lead 11 grams per cc. That means that for every cc replaced, you gain only 3 grams (a little over one swingweight point). Just for reference purposes, a 1cc hole is made by a 3/8" drill bit 1/2" deep. That's pretty severe surgery for most iron heads, and you only get three extra grams out of it.

     

Whether we're adding weight in a port, in the shaft tip, or taping it to the clubhead, we should bear in mind the amount of material we'll need to apply. Consider the table below:
 
Material Specific 
Gravity
Melting 
Point
Steel (most clubheads)
8

Solid tungsten
19

Tungsten powder
11

Pure Lead 11 326 C
50-50 Solder (Pb,Sn) 9 220 C
Wood's metal (Pb,Bi) 10 150 C
Lead/epoxy (50-50) 6

While epoxying is a technology familiar to every clubmaker, we shouldn't automatically be scared off by the thought of melting lead. It's easier than you think, and gives a much higher-density weight. You can melt it with your shaft-removal torch, and drip it into a mold of some sort -- or directly into the cavity, if possible. Solder, which is still heavier than a lead/epoxy paste, can be easily melted with an electric soldering iron.

It is probably worth noting that lead, absorbed repeatedly over long periods of time, is toxic. If you weight clubs with lead powder or by melting lead once or twice a year, this is no big deal. But, if you are a professional clubmaker who does this all the time, you need to treat lead as a hazardous material.
 

Decreasing heft

From the definition, we decrease swingweight by subtracting weight more than 14" from the butt or adding weight less than 14" from the butt. As noted above, swingweight modification at the butt, while it does affect both the calculated and measured swingweight, does nothing for the "heft" of the club in any constructive way. It doesn't affect the MOI -- the real, physics-based measure of heft -- nor does it show any effect in computer simulations. Heavy grips and butt weights affect the swingweight, but not the underlying heft factors. There may be other uses for butt weight for some golfers, but swingweight adjustment is not one of them.

So the only ways to decrease heft usefully are to reduce the shaft weight or length, or the clubhead weight. Consider:

  • Shaft weight is controllable, at some expense. Lightweight steel and graphite shafts offer a way to reduce swingweight. Weights range from the standard weight steel shafts, at 120-130 grams, to lightweight graphite, at 60-70 grams. There are even super-light shafts in the 50-gram range. That's a range of over ten swingweight points. But as the weight goes down the price goes up, especially if you want to keep torque constant. Moreover, it takes about three times the weight savings in the shaft to equal the swingweight impact of saving weight in the clubhead.
  •  
  • Clubhead weight is a lot harder to control. The total range of head weights is less than 10 grams, or five swingweight points, and the vast majority of component heads lie in a 3-gram range. (That's a 5-iron between 253 and 256 grams, and the rest of the irons on a 7-gram interval.)
  • One way of reducing head weight is grinding it off. I've done this with a grinding cylinder in a Dremel Moto-Tool, removing as much as 7 grams of steel. The best way is to remove material from the inner wall of the cavity-back, since the cavity walls are not structurally important. But have plenty of abrasive disks handy; you'll wear them out fast on the hard stainless steel used in most golf clubs. And don't try this trick on forged clubs, unless you're going to have them re-chromed immediately.

  • Shaft length can be reduced but, as we saw in the previous chapter, only if a shorter club and a more upright lie can be tolerated. For every degree of lie that the shaft is more upright, it can be a half inch shorter or three swingweight points lighter. Of course, you will still need to make sure the new, shorter length is still appropriate to the golfer. Then you must do a dynamic lie test to fine-tune the lie. After all, changing the length and lie changes the swing plane, so it may change the swing enough to knock off the one-degree-per-half-inch rule.

Design Example

OK, so you've decided what length club you need to build.

 From a completely different set of considerations, you've decided what swingweight it needs to be. (We'll use swingweight for this example, because it's a little harder than MOI.)

 All that remains now is to choose a compatible set of components from the catalog and build the clubs. Right? Well, maybe. Let's look at a challenging example of design to a simultaneous specification of length and swingweight.

 I'll focus on the case of long clubs, because that's where I've most frequently found a challenge in designing to both the right length and swingweight. Consider the problem of designing a set of irons for my son, who is very tall and requires clubs 1.5" over a nominal men's set. However, I don't want to give him anything that swings heavy. From experience, I know he does best with a D-1 or so.

 We'll work the problem for a 5-iron; I advise starting with a middle iron, because the solution that works for that club usually can be applied equally well to the longer and shorter irons. (This principle isn't as applicable when working with woods because most bags don't have a lot of them, and the driver is frequently designed quite differently from the others.)

 
Start with a "standard" sort of 5-iron:

"Usual" clubhead (say an Acer) 256 grams

True Temper Dynamic shaft 128 grams

"Standard" length for men's 5I 37.5 inches




Gives a swingweight of . . . . . D-0

No surprise that "standard" components will give a "standard" swingweight.

 But, when we add 1.5 inches to the length, the swingweight jumps to D-9. (Check with the sensitivity tables; 6 swingweight points per inch times 1.5 inches is 9 points.) To get to D-1, we have to do things to reduce the swingweight by about 8 points. Let's look at the different ways we could accomplish the design:

Lighter Clubhead

This is the first approach that comes to mind, because weight at the clubhead is a very strong determinant of swingweight. (If we were trying to increase swingweight instead of decreasing it, adding weight to the clubhead is the time-honored way of doing it.)

Unfortunately, there isn't too much available in this department. Many Golfsmith heads are down to 253 grams for the 5-iron, but I know nothing on the market any lighter.

Looking at the swingweight tables for cross-sensitivity, we see that saving 3 grams of head weight saves 2 swingweight points. We'd be down to D-7. Let's do it!

Lighter Shaft

We've saved all we can at the clubhead, where saving a gram really buys something. It takes 10 grams in the shaft to save a swingweight point. We're trying to get from D-7 to D-1, so we will need to save 60 grams. That means we need a 68-gram shaft (60 grams less than the "standard" 128g from the table).

Can we find shafts that light for irons? Well, they will be graphite, not steel, at that weight. And looking in the catalogs, we find they are available. But shafts that light tend to have a flex profile and torquethat are better suited to slower-swinging seniors and women, not a tall, strong athlete. An iron shaft that would fit my son for the other shaft specs (other than weight) will be 10-15 grams heavier, in the 78-83g range -- and there are a lot of choices there. So let's get something in that range, and resign ourselves to needing to still find an extra swingweight point or a bit more. (This was originally written in the 1990s. By 2013, it is not all that hard to find a decent graphite shaft for irons at or under 70g. They cost a little more, but you're still way ahead compared with brand name off-the-shelf clubs.)

It should be noted here that, while most steel shafts have a centered balance point, almost all graphite shafts have a balance point 3/4" to 1.5" higher than the middle of the shaft. That will reduce the swingweight further. For instance, raising the balance point by 1" on an 80g gram shaft will reduce the effective moment of the shaft by 80 gram-inches. Remembering that 50 gram-inches is one swingweight point, we may have achieved our target swingweight already.

In fact, we probably want to try the club out in this configuration. In many cases, a slightly higher swingweight than the one that gives optimum golf shots with give good golf shots -- and more more reliably. (That's experience more than theory.)

But suppose our testing shows that we really need to reduce the clubs by another point plus...

Upright Lie

We can't save any more swingweight by reducing weight, but maybe we can reduce the length. Yeah, I know we said 1.5" long but....

A lot of tall players learned their swing before they got a set of clubs built for their height. Those that did tend to have a rather upright swing plane. That means we already should have been thinking about an upright lie for them, but now we have additional motive. Remember that each degree of lie is worth 1/2".

Let's try it! We only need to reduce the club's swingweight by 1-1.5 points, which means reducing the length about 1/4 inch. That is only a half degree more upright. We know we are going to measure and set the lie angle dynamically after the clubs are finished. If a half degree error on the lie angle matters to you, then you can count on having to bend some of the clubs to match the golfer anyway. So the swing plane change due to 1/4" of length reduction is probably not going to change the amount of bending to get the clubs' lie angles right.

A more important consideration is whether the shorter, more upright club is good for the golfer. You can only find that out by having him hit balls. The choices at this point are:
  • The clubs are good at the target swingweight and 1/4" shorter than designed, with lie adjusted for the slightly more upright swing plane.
  • Go with the target length and one swingweight point heavy.
Frankly, the latter will usually be better in the long term, but only trying it out can tell which to do. In fact, both designs are very close at that point -- much closer than you'll ever be able to fit this golfer with off-the-rack clubs.


Notes:

  1. It may sound foolish and even patronizing to say that. When I wrote it, I felt like McDonalds lawyers must have felt after the lawsuit. "OK, let's print in large letters on all our coffee cups, 'HOT! DO NOT POUR IN YOUR LAP!'" But I actually got email from someone who went through the measurements.... then used my graph instead of making his own based on his [very different] measurements. Ouch!


Last modified June 10, 2013