Mike's questions -- Part 2:

How Much Distance are You Leaving Out There?

Dave Tutelman  --  December 27, 2014
This work was instigated by a couple of questions asked by Mike Stachura. He wanted to know how many yards of driving distance you get for every mile per hour of clubhead speed, and also how many extra yards of driving distance could a golfer pick up without increasing clubhead speed.

Mike's second question is, How much driving distance does the average golfer "leave on the table", assuming his/her clubhead speed is what it is and won't increase?

Here is a bit of further explanation of what is behind his questions, excerpted from another email.

Assumptions and approach

Answering the second question requires flipping the whole approach from the first question on its head. For the first question, we assumed away or defined away everything except the clubhead speed, and saw what clubhead speed does for driving distance. Now we have to do just the opposite: define the clubhead speed as constant, and see the effect we get from everything else.

In discussions with Mike, we clarified the ground rules of the question. Remember, the spirit of the question is, "I can't change my clubhead speed, but anything else within the Rule of Golf is fair game.
  • Changing parameters of the club within the rules is allowed. Your driver may may fit you poorly, or it may just not have all the technological improvements up to date.
  • Learning to do things better with your swing is allowed, though we will rule clubhead speed improvements to be out of bounds. Yes, that's arbitrary, but not necessarily a bad idea. We will find some things to work on that could help more than a couple of MPH of clubhead speed. And sometimes working on speed distracts us from these other distance-important skills.
We will assume a few things, but not nearly as many as for question #1.
  • We have a relatively modern driver and ball. They combine for a coefficient of restitution (COR) of 0.83.
  • The same plain vanilla ambient conditions as for question #1: temperature 80F, sea level, no wind, flat fairway, no elevation of tee box, etc.
Here are the things we will investigate:
  1. Better contact on the clubface. (Learning and Equipment)
  2. Proper clubhead loft (Equipment)
  3. Raise the angle of attack. (Learning)
  4. Lower the center of gravity of the clubhead. (Equipment)
  5. Hit the ball above the center of the face. (Learning)
For each, we will see how much distance we stand to gain. Unfortunately, the tool that I use for most of this study only computes carry distance. So we will see how much carry distance we might gain, but not total distance. At the end, I will give some qualitative feel for total distance, but I'm afraid I don't know enough to quantify it right now. If and when I know more, I will update the article.

This is an investigation of things we can do to improve distance without increasing clubhead speed. So we will have to pick a clubhead speed. Since I have computed the graph for a launch space at an 86mph clubhead speed, that is what we will use. I would expect the gains at different clubhead speeds to be sort of proportional to the ones we find, but that is just a guess. We would have to construct the launch space for that speed and go through the drill to really know.

Let's go through the five areas of improvement described above, and see how much yardage we leave on the table.

1 - Better contact on the clubface

One of Mike's emails said:

We will start with smash factor. As Mike notes, this could be due to poor instruction or an ill-fitting driver -- or both. First let's quantify the damage, then we'll think about the cause.

If our 86mph golfer has the average golfer's smash factor of 1.41, that means that they are leaving 12 yards on the table.

How did I come up with that number? Remember the answer to question #1 included the fact that you get 2 yards of increased carry distance for every MPH of increased ball speed. Let's do the calculations:

BallSpeed = ClubheadSpeed * SmashFactor

So let's figure ball speed for the ideal smash factor of 1.48, and again for our golfer's smash factor of 1.41.

BallSpeed = 86 * 1.48 = 127.28
BallSpeed = 86 * 1.41 = 121.26

That is 6mph we are losing because of imperfect ball contact. At 2 yards for each MPH, a loss of 6mph is a loss of 12 yards of carry distance.

(Notice how easy it is if we are just looking at gains and losses. We don't even have to worry about the y-intercept, just the slope.)

Let me take a moment to discuss Mike's survey result of a 1.41 smash factor. Here are some clubfaces showing impact marks, reported by Tom Stickney II in a January 2014 GolfWRX article "Impact location by handicap" .



From experience, I would guess that the Tour Pro has close to a 1.48 smash factor, and the 7 handicap somewhere in the mid to low 1.4 range. I would be surprised if the 15 handicap is over 1.30. At a 1.30 smash factor, the yardage loss is more like 30 yards. That is a lot!

Causes and cures

A poor smash factor comes from imperfect contact between ball and clubface. This could be a combination of an off-center strike or the clubface not being square with the clubhead path. Either way, you will lose ball speed and distance. And either way, it might be your swing or your driver. In fact, a poorly fit club can even be the root cause of a poor swing -- a swing that compensates for the club's deficiencies.

So the first step to finding these 12 lost yards is to get a driver that fits you. Not necessarily the latest in technology (we'll get to that later), but one that you can swing well enough to repeat your swing consistently and square the clubface to the path.

Once you have that, you can learn to make that consistent contact on the sweet spot so you don't lose distance. Consistency has to come first, then learn where to apply the clubface. I have stories about that sequence, one about learning and one about clubs.

Learning to hit the sweet spot: John Ford of The Golf Institute in Lady Lake FL is a friend whose business is clubfitting, but who gives lessons along with the fitting. (Many good clubfitters measure for the best the golfer can do, and that involves instruction during the fitting.) His specialty is not changing the swing, but rather encouraging whatever swing that golfer can repeat, then teaching him/her how to hit the sweet spot consistently with that swing. He tells me, "Dave, I do it every day." I use a variant of his approach, and it works for me.

How does John teach golfers to hit the sweet spot consistently? There are three requirements: a consistent swing, a setup that leaves you a consistent distance from the ball, and a fine-tuning of that distance so that your swing gets the sweet spot. John's approach to each requirement:
  1. Consistent swing: John doesn't try to tinker with your swing. Instead, he custom-builds clubs to you that fit the swing you have and are comfortable making. No compensations in the swing to allow for clubs that don't quite fit it. That means it is easy to make the same swing every time. It may not be the most powerful nor efficient swing, but it is consistent enough to begin the search for a high smash factor.
  2. Repeatable impact: If you have a consistent swing, you should make consistent impact, right? Well, almost right. If you always set up the same distance from the ball and always make the same swing, the impact should be consistent. During the final fitting and testing of the clubs, John teaches a pre-shot routine, a setup technique, that assures you are the the same distance from the ball every time. (This is subject, of course, to the length of the club; the routine accounts for different club lengths.) Then he checks the consistency using impact tape, making sure the impacts are at the same spot on the clubface.
  3. Centered impact: We're still not there, but the hard part is done. Not everybody has a swing where the clubhead at impact is in the same position it was at address. In fact, such swings are relatively rare among golfers in general. Suppose you set up with the ball perfectly centered at address, but always hit the ball a half inch toward the toe. (That happens to be the most common pattern among mid- and high-handicap golfers.) John has found you can fix this by setting up consistently, but with the ball a half inch toward the heel, to allow for the toward-the-toe impact. The result is a center-face strike.

    John has a patent (No. 6,471,599, Oct 2002) on a clubhead to aid this process. His custom clubs have a head with a row of recessed dots in the topline, shown in the illustration. If the impact tape in step #2 shows that impact is N dots in one direction on the clubface, John puts a drop of red paint in the recess N dots in the other direction. For instance, if you are hitting 2 dots toward the toe, he will put paint 2 dots toward the heel, and teach you to set up with the ball opposite the dot (instead of centered in the clubface). It works very well.
Clubs that make it hard to hit the sweet spot: I did a study a few years ago focused on how much extra distance is available by using a longer driver. I started with a survey of papers in the field, and did some computer modeling myself. I looked at anecdotes from clubfitters, and even interviewed a couple of long-drive competitors. There was a considerable disparity in the results of these studies, almost as much disagreement as agreement.

In the interest of bringing some unity to the conclusions, I experimented with long drivers myself. I needed to in order to decide which conflicting data and anecdotes to believe. I concluded that a common and important theme is that extra length (which has become the norm in commercial drivers these days) plays havoc with smash factor. You will probably hit the occasional big drive, as much as 10-12 yards further than you are used to. But unless you are well-fit to a long club, or practice a lot to learn to hit the sweet spot, you will lose distance on average because of lousy smash factor. Here is some representative data from FlightScope tests I did with my own clubs and swing.


This scatter plot shows clubhead speed vs ball speed for a number of swings. As all studies predicted, the longer driver develops more clubhead speed than the shorter one. In spite of the increased clubhead speed, I got lower ball speed -- which means less distance.


If anybody wonders about the reason for the drop in ball speed, here are the impact tapes from the faces of the drivers. Any questions?

I was having a bad swing day when we did the tests. None of the drives, with either club, equaled Mike's average smash factor of 1.41. But even on a good swing day, I only get a few drives from the longer driver with noticeably more distance than the shorter driver. And I lose distance on average.

In fact, I have found that the long driver is a better training aid than golf club. If I play a round with the long driver, the following round (with the shorter driver) is usually a very good driving day, both more consistent and longer than usual.

Potential gain

By all means, the most productive thing most golfers can do to gain distance is to improve their impact between ball and clubface. If you have the average random golfer's smash factor of 1.41 with your driver, you can pick up 12 yards from smash factor alone. If your smash factor is worse, you can pick up more.

What we did Carry distance Improvement
Baseline -- 0
Improve impact -- +12 yd

Launch space

The rest of the improvements we will work on require improving the launch angle and spin. To evaluate that, we need to become familiar with a graph I call "launch space". We will use this tool for most of the distance gain evaluations. I am borrowing here a tutorial on launch space from another of my articles.

Launch space is the three-dimensional graph of distance vs both launch angle and spin. A launch space is a graph for a specific ball speed. But it could also be for a specific clubhead speed if we assume a smash factor.[1]

For this study, we will be working with a clubhead speed of 86mph with a nearly ideal smash factor of 1.47. Why? Because launch space graphs are a lot of  work to construct, and I had one lying around for 86mph.

The launch space graph (shown here) is three-dimensional, with launch angle and spin being the horizontal axes and distance the vertical axis. We need it to answer Mike's question because -- except for very fundamental stuff like hitting the ball with the clubface -- any distance gain we hope to make will happen by changing launch angle and spin. The launch space graph tells us what any change of launch angle and spin will do to distance, which is exactly what we need for this work.

So let's explore what a typical launch space looks like.

As conventional wisdom leads us to expect, the highest point on the graph is where the launch angle is highest and the spin is lowest. But the converse is not true; the low point of the graph is not the opposite corner, of low launch and high spin. Rather, it is the "off corners", at high launch and spin, and low launch and spin. There is a diagonal "ridge" of fairly high distance, and falling off the ridge on either side loses distance much faster than simply climbing down along the ridge. This is perhaps better seen in a two-dimensional color-coded map of the graph, so let's look at that.


The colors denote classes of distance as they move through the rainbow: red for long distance and purple for short drives. we can see the ridge -- the black dotted line -- that goes from high-launch/low-spin down to low-launch/high-spin. The distance changes rather slowly as you move along the ridge, but falls off rapidly on either side. That is why it is called a ridge.

As we look for ways to get more distance, we will become very familiar with this launch space.

2 - Proper clubhead loft

This typical golfer of ours... what kind of driver does he use? It's probably a brand name driver bought off-the-shelf, with the most common loft of 10.5. Is this the right loft, the best loft for distance? We can use the launch space graph to find out.

Let's start by mapping a driver onto the launch space? We start by mapping just the dynamic loft at the given clubhead speed of 86mph, keeping everything else neutral.
Using TrajectoWare Drive, we get the following points on the line:
Dynamic loft Launch angle Backspin
8 7.2 1915
10 8.9 2389
12 10.5 2861
14 12.0 3329
16 13.5 3793
18 15 4252
20 16.4 4706
22 17.7 5155


The result is a line, the locus of the lofts in launch space. In the launch space graph below, the red balls are labeled with the loft they represent, from 8 to 22. Each loft is placed at the launch angle and spin produced by the driver. You can read the distance from the nearby cells in the launch space map. For instance, 14 gives a carry distance of 188 yards, and 18 about 185 yards.




The important thing to note here is that varying the loft changes both launch angle and spin in the same direction. An increase in loft increases both launch angle and spin. Therefore, the line of possible lofts crosses the ridge almost at a right angle. It isn't anything like parallel to the ridge; just the opposite, in fact. There is no opportunity here to move along the ridge -- to increase distance by playing with increased launch and decreased spin.

If we were to use loft alone to optimize the driver, we would choose the point where the locus of lofts intersects the ridge of maximum distance. For this golfer -- who swings at 86mph, remember -- we would use a loft of 15, giving a carry distance of 189 yards.

Details of the cure

A lot of optimization efforts stop here, and it's not a bad place to stop. Already, it probably suggests more loft than the player is using; that has been my experience, and it will tack on a few yards. But we won't stop here; we want to see how much distance we can wring out of proper club choice and a bit of fiddling with the swing.

Before we go any further, we need to know what the golfer is actually doing at impact. We assume a zero angle of attack (so far, anyway). But there are other factors that go into dynamic loft, which is the loft the ball sees at impact. Remember, the ball doesn't know what club you used, or how good a swing you made. All it knows is what the clubhead is doing at impact. So let's list the things that could affect the dynamic loft:
  • The loft of the clubhead. That may or may not be the actual loft stamped on the sole; there is such a thing as a "vanity loft", a loft labeled stronger than it really is so the owner can feel macho and still hit a decent drive. The loft we need to optimize distance is the real loft.
  • The angle of attack, of course. But (so far) we are assuming it is zero.
  • Shaft bend. This might add a few degrees to the dynamic loft, depending on the swing and the shaft flex. In most cases, it adds about 2.
  • Wrist position. A cupped or bowed wrist at impact usually has more effect on AoA than on loft, but it can have some effect on loft.
So our average golfer is using a 10.5 driver. Let's assume that the shaft bend adds 2 to the dynamic loft, and the other effects are negligible. So the effective loft of the driver at impact is 12.5.

The launch space tells us we need a loft of 15, and that includes the 2 bend of the shaft. So we need a 13 driver head.

Potential gain

We are going from a dynamic loft of 12.5 to 15. Find where 12.5 would be on the launch space graph; it is 1/4 of the way from the 12 circle to the 14 circle. That would correspond to a carry distance of about 183 yards. And we already know that the optimum loft of 15 gives a carry distance of 189 yards. So we have gained another 6 yards.

Here are the gains so far.
What we did Carry distance
(yards)
Improvement
(yards)
Cumulative
improvement
Baseline 171 0 0
Improve impact 183 +12 +12
Fit the right loft 189 +6 +18

Let's keep going with our improvement program. The gains will be smaller and harder to come by, but they are there.

3 - Raise the angle of attack

It is generally known that a higher angle of attack can be used to lower spin and/or raise the launch angle -- which is exactly what we want to do to increase distance. At this point in the optimization, we need both increased launch and decreased spin; fiddling with the loft can only give us one at the expense of the other. So let's try for a modest gain.

Suppose I could improve my AoA by 2, from 0 to +2, with no loss of speed nor reliability. With enough instruction and practice, that might be achievable by our typical golfer. I know teaching pros who can vary AoA at will from -5 to +5. But we're talking about the typical golfer here; an additional 2 is enough of a challenge.

Let's see what this would mean in launch space. Adding 2 to AoA increases the launch angle by 2 with no change in spin. So it moves us to the right in launch space by 2. Let's show this in launch space; we will move the driver dots 2 to the right.



In the launch space diagram, I have moved the driver lofts 2 to the right. I left in the old lofts as pink "ghosts", so we can see where we were before.

Now the maximum distace occurs at a 14 dynamic loft, down 1 from before. The distance achieved is 193 yards, a gain of 4 yards.

Here is something worth noting. The additional angle of attack can be used either of two ways, or a combination:
  • Increase the launch angle by the angle of attack, with no spin penalty.
  • Decrease the loft, and get the same launch angle with a lower spin.
  • A combination, splitting the difference between a small increase of launch angle and a small decrease in spin.
In this case, the best choice was a combination. We increased the AoA by 2 and decreased the loft by only one of those degrees. We know it was the best choice not because we tried both; we looked at the launch space and the optimum was visually apparent.

Potential gain

The increase of 2 in Attack Angle was split between increasing the launch angle and lowering spin. The result was a 4-yard gain in carry distance.

Here are the gains so far.
What we did Carry distance
(yards)
Improvement
(yards)
Cumulative
improvement
Baseline 171 -- 0
Improve impact 183 +12 +12
Fit the right loft 189 +6 +18
Increase attack angle 2 193 +4 +22

Gear effect

There is one more thing to play with here, and that is vertical gear effect. Here's a quick primer, in case you don't know what that is.

When the clubhead strikes the ball, the clubhead and ball exert large forces on one another; the force could easily be 2000 pounds. If the impact force goes through the center of gravity (CG) of the clubhead, then the clubhead glides through impact without being thrown off course.

But suppose the force is above the CG, as the picture shows? That applies a torque to the clubhead, wanting to rotate the head around the CG to a face up position. And it does rotate the head (the purple arrow), because the forces are briefly so much greater than the shaft's ability to resist them.

With the ball compressed on the clubface, the clubhead and ball are like two gears engaged together. So the counter-clockwise (in the diagram) rotation of the clubhead will cause a clockwise rotation of the ball. That is topspin. There is not enough topspin from gear effect to completely overcome the backspin due to the loft of the clubhead. But the backspin can be considerably reduced by the gear effect topspin.

Conversely, if impact is low on the clubface, the ball will start its flight with even more backspin than the loft supplies. Again, there is gear effect, but the clubhead rotates face down and the gear effect applies additional backspin.

The amount of the gear effect depends mostly on where the impact force is compared to the center of gravity. The more above the CG the force is, the more the gear effect topspin -- thus the smaller the net backspin the ball has. Other things that figure into the gear effect spin are:
  • Exact position of the CG.
  • Moment of inertia of the clubhead.
  • Clubhead speed at impact.
If you want more detail on gear effect, including the math involved, see my article on the subject.

So what?

How does gear effect get me more distance? Now we know that it can reduce backspin. And we know from the launch space that reducing backspin without reducing launch angle can be used to move along the ridge of maximum distance. So let's explore two ways we can get gear effect topspin, and see what they do for us:
  1. Build more gear effect into the driver -- specifically, lower the center of gravity of the clubhead.
  2. Use more gear effect in your swing -- specifically, strike the ball high on the clubface.
One is equipment, the other is learned technique. We'll look at both.

4 - Lower the center of gravity of the clubhead

In early 2012, Jeff Summitt asked me some questions about the effect of CG placement. That led to a multi-page article that characterizes how the position of the CG manipulates the gear effect spin. There is even an Excel spreadsheet that you can download to calculate spin from the CG position. Let's go through that exercise now, to see what a 0.1" lowering of the CG can do to help us increase distance. (Jeff assures me that lowering the CG a tenth of an inch is a real design challenge, so I'm reluctant to evaluate a more dramatic change.)

I used the Excel spreadsheet to quantify the  gear effect spin due to moving the center of gravity downward. No matter where on the clubface the ball was struck, it reduced the backspin by between 410 and 430rpm. In the center of the clubface, it reduced backspin by 427rpm.

To see how this affects distance, we turn again to the launch space graph. This time, we move downward in spin by 427rpm from each of the feasible loft "balls".



If we look at the 14 loft that was best for us in the attack angle exercise, moving the CG down actually loses a bit of distance. We were right on the ridge of maximum distance, at 193 yards. Reducing the spin drops us below 192 yards. But we can still use this to improve distance; we just have to increase loft, so the decreased spin moves us back to the ridge.

If we loft up to 15.5 or even 16, we will get the distance up to 195 yards. That's a small gain, but still a gain.

This finding agrees with the "loft up" campaign that TaylorMade launched to promote the SLDR driver. The SLDR lowered the center of gravity of the clubhead. (Don't worry right now about "down and forward" vs "down and back"; the forward-back does not produce nearly as much spin change as just plain "down" does.) I know people who tried the SLDR and said, "I don't know what's wrong, but I lost distance with it. I got rid of it." When I quizzed them further, they said, "The crazy salesman wanted me to get a 14 degree loft. I know the right loft for me is 10.5, so I got a 10.5 SLDR." Well of course you lost distance. At a 10.5 loft, you're in the part of the launch space where reduced spin hurts rather than helps. You're already well below the ridge; moving down another 427rpm will just make matters worse.

Potential gain

Lowering the center of gravity by 0.1" reduced spin by over 400rpm. But that does not help distance by itself. We had to bump up the loft to increase the launch angle; otherwise, the decreased spin actually hurt distance. When we combined the decreased spin with increased loft, the result was a 2-yard gain in carry distance.

Here are the gains so far.
What we did Carry distance
(yards)
Improvement
(yards)
Cumulative
improvement
Baseline 171 -- 0
Improve impact 183 +12 +12
Fit the right loft 189 +6 +18
Increase attack angle 2 193 +4 +22
Lower CG by 0.1" 195 +2 +24

5 - Hit the ball above the center of the face

The spin reduction we get from gear effect is proportional to how far the impact force is above the center of gravity. There are two ways to make this bigger: lower the center of gravity or raise the impact point. Our improvement #4 was a club improvement, lower the CG. Now let's look at the other side, raising the impact point.

This is dependent on the golfer's skill, not on technologically advanced equipment. If the golfer was able to learn to hit the center of the face consistently, then hitting a half inch above the center of the face should be a similar challenge, and similarly mastered. In fact, it can be accomplished with the same swing and the ball teed a half inch higher.

Hitting higher on the clubface gives both a spin reduction and a launch angle increase. Here's why.
  • The spin reduction should not be surprising. We're putting more vertical distance between the impact force and the CG, so we should get more gear effect topspin to work against the backspin.
  • The launch angle increase is due to the fact that the clubface is curved. The typical commercial driver has bulge (horizontal curvature) and roll (vertical curvature). If we hit higher on the face, then we encounter a higher loft -- hence a higher launch angle.
The diagram shows how face curvature affects loft, depending on where on the face you hit the ball. It is clear just by looking that the lower ball strike (the red lines) occurs at a lower loft than the higher strike (the green lines). It may not look like much, but it is. Most drivers are built with face roll at a 10-12" radius. At an 11" radius, a half inch of height is worth two and a half degrees of loft. The full face height of two inchs spans a loft difference of ten degrees of loft. That is a lot.

As before, we will quantify the improvement by using the launch space graph. And we will use the Excel spreadsheet to tell us where to move in launch space. We are going to move the impact point from the center of the clubface (the point of nominal loft and no gear effect) to a point a half inch above it. According to the spreadsheet, that moves us in launch space:
  • 2 higher launch angle. That is motion to the right on the launch space graph.
  • 1100rpm less spin. That is motion downward on the launch space graph.
Let's see what the launch space looks like.


The green arrows were sized and angled to move 2 right and 1100rpm down. The tips of those arrows are what we can achieve by hitting a half inch above center. (I am assuming that the COR of the clubface is maintained at least " away from the center of the clubface. That is a reasonable assumption with today's drivers.) Look at the arrowhead on the ridge. It shows a carry distance of 201 yards. That is a substantial improvement over our previous best distance. And it requires increasing the loft at least 2 to 18 -- even though we get another 2 of launch angle just from face curvature. We need the additional loft to keep us on the ridge.

Let's remember that this is not really an 18 driver. It's a 16 driver head, with another 2 of dynamic loft coming from shaft bend. But still, how many 16 driver heads do you see out there? If we are going to "loft up", we need more clubheads available with the necessary loft. But remember, this is carry distance. I believe that, once I understand total distance quantitatively, maximizing total distance will require a somewhat lower loft. So the optimum driver will not be quite as extreme.

Potential gain

Raising the impact point on the clubface by 1/2" gave us a substantial increase in carry distance. It increased the launch angle by 2, at the same time it reduced spin by 1100rpm. That is huge. And the result was a 6-yd gain.

Here are the gains we have managed to achieve. This is what the typical golfer with an 86mph clubhead speed leaves on the table.



Discussion and additional topics

If you were looking for the answer to Mike's question, now you know. The typical golfer we chose (86mph clubhead speed, 10.5 driver, 1.41 smash factor) is leaving 30 yards "out there". That's 15% of his/her potential distance.

But there are things still to be said that I find interesting, and you might too. You can skip this part or read what grabs your attention.

Where the gains came from

Here's another version of our results table.
What we did Carry
distance
(yards)
Improvement
(percentage
of total)
Type
of
effort
Baseline 171 -- --
Improve impact 183 40% Learning,
club fitting
Fit the right loft 189 20% Club fitting
Increase attack angle 2 193 13% Learning
Lower CG by 0.1" 195 7% Club design
Raise impact on the face by 1/2" 201 20% Learning

We can see that the relative contributions of learning and equipment can be anywhere from 3:1 to 1:2, depending on their relative contributions in improving the smash factor. If  the lower-than-optimum smash factor was due to ill fitting clubs, then equipment accounted for 2/3 of the improvement (40+20+7=67%). If, on the other hand, the clubs fit reasonably and the improved smash factor was from learning and practice, then learning accounted for almost 3/4 of the improvement (40+13+20=73%).

Smash factor

Let me make a further guess -- but only a guess -- that if both equipment and technique were the cause of the poor smash factor, then the starting smash factor was lower than 1.41. The split may be closer to 50:50, but the total gain was significantly larger. For instance, starting with a 1.30 smash factor means that there is 30 yards to be reclaimed from smash factor alone!

In fact, let's see what the tradeoff is between clubhead speed and smash factor. If going for more clubhead speed prevents us from getting consistent, good impact, which is more valuable? Here's a table that gives us the answer in plain numbers.

Clubhead
speed
Gain in smash factor
0.05 0.10 0.15 0.20 0.25 0.30
70 2.2 4.4 6.6 8.9 11.1 13.3
80 2.5 5.1 7.6 10.1 12.7 15.2
90 2.8 5.7 8.5 11.4 14.2 17.1
100 3.2 6.3 9.5 12.7 15.8 19.0
110 3.5 7.0 10.4 13.9 17.4 20.9
120 3.8 7.6 11.4 15.2 19.0 22.8

This requires a little explanation, so here it is.
  • The yellow numbers are your current clubhead speed in MPH.
  • The blue numbers are the amount in smash factor that you gained or lost. For instance, if you improved from 1.35 to 1.45, that would be a gain of 0.10.
  • The white numbers are MPH of clubhead speed you would need to gain in order to get the same distance as that gain in smash factor.
Let's look at an example:
Suppose you have a clubhead speed of 100mph and a smash factor of 1.35. (This is fairly common. In fact, it probably described me a decade younger.) Improving your smash factor from 1.35 to 1.45 (a gain of 0.10) will give you the same distance as if you improved your clubhead speed by 6.3mph, to more than 106mph. 6.3 is the entry in the table for clubhead speed = 100mph and gain in smash factor = 0.10.

A 6.3mph gain of clubhead speed is significant! It requires a lot of work, practice, conditioning, etc. And it won't get you any more distance than a 0.10 improvement in your smash factor!

For those interested in how we compute this, see note [3] below.

Spin, launch angle, and loft

Here's an observation about the last three improvements, the ones made after we got a good smash factor and decent first approximation to the correct loft.
  • When our improvement caused an increase in launch angle, that did not necessarily increase the distance. We had to decrease the loft to get back to the ridge.
  • When our improvement caused a reduction in spin, that did not necessarily increase the distance. We had to increase the loft to get back to the ridge.
  • Even our combined launch angle/spin improvement required a loft adjustment to consolidate the maximum improvement.
The takeaway is that all these distance tweaks require getting to the ridge and staying on the ridge to maximize the gains.

Another comment on spin and launch angle. Except for smash factor, our improvements consisted of finding higher launch angles and/or lower spin. But, as noted above, we had to adjust the loft to stay on the ridge. In describing the launch tests of 150 random golfers, Mike said:
If you have a low launch, you better have a high spin. This is a case of two wrongs making a right. You'll need the spin to stay on the ridge. Let's take an extreme example using our 86mph golfer. By the time all the improvements were made, the good drives launched at 19 and had 2700rpm of backspin. But if the same headspeed launched a ball at an angle of only 10, that same "proper" spin would not be proper at all. The ideal spin -- given that you screwed up the launch angle -- would be 3700rpm, a full 1000rpm higher, and well above the common wisdom's rule of thumb. Here's a table of a few points, along with the launch space we've been working with. The purple arrows show the movement in launch space.


What? Launch
angle
Backspin Distance
Best drive for
 86mph clubhead speed
19 2700rpm 201yd
Drop the launch to 10,
 same spin
10 2700rpm 175yd
Fix the spin to
 optimum at 10
10 3700rpm 183yd
Fix the spin instead
 by changing the loft
12 3400rpm 188yd

No, we don't get back most of the distance we lost. But, in this case, the very high spin helps rather than hurts. We do get back some of our lost distance.

When someone hits some good drives, and some low drives with much higher spin using the same club, it is almost always due to a low-face impact. The face curvature reduces the launch angle low on the face. Fortunately, there is gear effect. The low strike will generate more backspin, and things won't be quite as bad as if all you changed was launch angle.

There is even a nice, intuitive explanation for why you want high spin if you launch too low. A low drive wants to fall to earth fairly fast. The spin provides lift that keeps the ball in the air as a "frozen rope", not just a stupid low duff.

Carry vs total yards

Mike asked his question about total distance, not carry distance. I answered in terms of carry distance. As I said, my tools don't give total yards, but I do have a sense of what improves the rollout after landing. We want to decrease the angle of descent, and we want to decrease the backspin at the point of landing. A lower loft will help both. Here is my heuristic. I haven't done scientific tests on it -- and I probably should -- but it has produced pretty good results in practice.

When I have the driver designed for the golfer based on carry distance, I back off to one or two degrees lower loft. That drops the angle of descent and the final backspin, which will increase the runout. Let's look at an example; we'll take the final optimization we have done here for the 86mph golfer. The final loft is 18. Let's look at what happens there, and also at 17 and 16.

Launch Landing
Dynamic
Loft
Launch
angle
Spin Descent
angle
Spin Carry
distance
18 19 2700 40.2 2000 201
17 18.2 2500 37.9 1850 200
16 17.4 2250 35.2 1700 199

So each degree of reduced loft cuts angle of descent by two and a half degrees and final spin by 150rpm. But we only give up a yard of carry for each degree of reduced loft, at least this close to the optimum. That is probably a good tradeoff; we will probably get back more than that in improved runout.

I compared this strategy with the TrackMan data. They have separate optimizers for total distance and carry distance[2], and I looked at how the lofts differed between optimized carry and optimized total distance. After looking at their data, it looks like the same strategy would work, but be even more agressive. Back off 2 of loft at the high speeds and as much as 4 at the low speeds. By doing that, you might get another 17-19 yards total distance, above and beyond what carry distance optimization gives. You give up some carry distance, but gain a lot more in runout.

Since the TrackMan data is based on PGA Tour fairways, it includes more runout than the fairways you probably play. I haven't worked the problem in detail, but my intuition is that most golfers will optimize total distance a little closer to the optimum carry conditions than the TrackMan chart suggests. So maybe backing off from maximum carry by 1-2 degrees is the best strategy for most of us.

I wish I could quantify it better for you, but I can't for now. That's on the agenda, starting with a more thorough analysis of the TrackMan data.


Notes

  1. In fact, the launch space is valid for a ball speed. In claiming we have a launch space for a clubhead speed, we are ignoring 1 or 2 mph of change in ball speed, due to reduction of smash factor as the loft increases. The changes in distance, and the movement in launch space to achieve the change, is almost unaffected by this detail.
  2. TrackMan has in the past published an optimization table for driving distance. Two tables in fact: one for optimizing carry distance and one for total distance. The tables, created by TrackMan's Justin Padjen, used to be on the TrackMan web site. It is no longer there; the optimization function is included in the product itself. Nevertheless, it is still available on lots of sites. For instance, a Tom Wishon article at GolfWRX includes both charts.
  3. Here is how we computed the tradeoff between clubhead speed and smash factor. Let's start by looking at the change in distance due to smash factor. We know that smash factor affects ball speed, and now we know how a change in ball speed affects distance (from the answer to Mike's first question). In the algebra below "delta-something" (shown as Δsomething) refers to the size of a change in that something. That is common notation in algebra, calculus, and science.
    ΔVb  =  (Smash1 * Vc) - (Smash2 * Vc)  =  ΔSmash * Vc
    ΔDist  =  2 * ΔVb
    Thus:
    ΔDist  =  2 * ΔSmash * Vc
    Similarly, the answer to Mike's first question told us how changes in clubhead speed affects distance
    ΔDist  =  3.16 * ΔVc  
    In order to have a tradeoff, the ΔDist due to ball speed must be set equal to the ΔDist due to clubhead speed. Therefore:
    2 * ΔSmash * Vc  =  3.16 * ΔVc
    Solving this for the change in clubhead speed, we get:
    ΔVc  =   2

    3.16
     ΔSmash * Vc
    This is the formula we used for computing the cells in the table.

Last updated - Jan 12, 2015