Golf Swing Physics

4. Technology

Guest article by Rod White  --  December 2008

Golf has always been a game of technology, with a long history of improvements to golf balls and clubs. However it is easy to be sceptical of the impact technology has had – surely coaching and swings have improved too.

On this page we look at some of the effect of some of the recent technological changes on golf driving distances.

The pink curve on the graph shows the mean driving distance for PGA tour professionals for every year between 1980 and 2008. The two curves either side show the average plus and minus 1 standard deviation (a measure of the variation amongst the golfers). The dots show the average driving distance for the longest driver of the year.

The graphs show a consistent increase of about 40m with much of that occurring between 1995 and 2005. How much of that gain is due to technology?

Clubhead Mass

As we should expect from the simple model we developed earlier, the driving distances are more or less independent of club head mass. As the club-head mass increases, the swing efficiency increases (more kinetic energy transferred the clubhead), and the collision efficiency falls.

The chart shows that there is a maximum between 170 and 180 g, but it is a very broad peak. That is, you have to get a long way from the peak before it makes a lot of difference. Any club head mass between 130 g and 240 g yields the same distance within about 4 m.

The optimal mass not only gives the greatest distance, it also means that the same club will do for almost all golfers (which is good news for the club manufacturers).

The optimum mass indicated in the figure is still a little short of the 195 g to 205 g typical of modern drivers. There are a couple of reasons for this. Firstly, muscles work better at slower speeds, favouring a slightly heavier club and slower swing. Secondly, the driven pendulum model used to produce the graph assumes a constant shoulder torque. In reality it will take a short while for the shoulder torque to build so that more of the work is done at the end of the swing where it is not transferred efficiently, and the lower efficiency results in a heavier optimum mass. Finally, the value I chose for the effective mass of the golfer’s arms is a nominal value that had been used previously by other researchers, a 20% increase in arm mass is sufficient to account for the difference.

Shaft Length

The effective shaft length used in the graph is defined by the point where the arms and the club hinge, and can be a couple of inches less than the full length of the club.

We have already mentioned the increase in efficiency that accompanies increased shaft length. In fact, increasing the shaft length increases driving distances through two effects:
  1. An increased downswing angle – which means that more work is done by the golfer, and
  2. The improved efficiency of the swing – a greater fraction of the work done by the golfer is transferred to the club head.
The total work done by the golfer is downswing angle x shoulder torque, and clubs with a longer shaft take a longer time to swing out, and results in a greater down-swing angle, and hence greater work done by the golfer. However, a natural release swing (with no wrist torque) becomes anatomically impossible with long shafts. For the average male golfer, most of the modern standard length drivers (45-46”) are a little long, although this depends a lot on the golfer's grip and the location of the centre of the hinge at the wrists.

A number of professional golfers have observed that their driving accuracy improves with shorter shafts. This is probably due to a reduction in the use of the hands.

Coefficient of Restitution

By far the largest contribution to increased driving distances has come about from the improved Coefficient of Restitution (CoR) of the club-ball collision. At the time of the introduction of the solid core ball, the CoR of most balls was in the low 0.7 range. As rubbers improved, the CoR improved markedly. During this time, manufacturers had to compromise between a soft skin (better spin control) and distance (with a harder, longer wearing skin). Nowadays it is possible to achieve the maximum CoR permitted under the rules while still having a soft skin.

The rules have two tests on balls, one based on ball velocity after a well defined impact with a solid steel object moving at a prescribed speed. This limits the CoR of the ball (in collision with solid steel) to about 0.79. The second limits the driving distance with a specified driving machine.

With the development of metal drivers, it became possible to build large thin club faces with a resonant frequency low enough that they would flex and store energy during impact. This "trampoline effect" reduces the compressive forces on the ball, and therefore reduces the energy dissipated in the collision. As a consequence of the trampoline effect, the CoR for the combined club-ball collision has risen to about 0.83 -- where it is now limited by rule.

This means, since the 1970’s the improved CoR has resulted in a 20m increase in driving distances for the average golfer.

Shaft Material

Another of the major technological advances has been the change from stainless steel shafts to graphite shafts.. The effect is due to an improvement in the swing efficiency.

The club-ball collision time for a typical drive is below 0.0005 seconds. During this time, the kinetic energy must be carried from all parts of the clubhead to the ball. You can envisage this happening as a compression wave in the metal clubhead carrying the energy forward. The same is true for the first few inches of the shaft. However, most of the kinetic energy in the shaft cannot be carried into the head and to the ball because the speed of the wave, carrying the energy from the shaft, is too slow. So the great majority of the shaft's mass is not involved in momentum transfer to the ball. This means that all of the work done by the golfer to put kinetic energy into the shaft is wasted -- it does not participate in energy transfer to the ball -- and reducing the mass of the shaft will make the stroke more efficient.

Reducing the shaft mass from about 130 g (steel shafts) to about 60 g in modern lightweight shafts has resulted in an increased driving distance of about 10m.

Note: contrary to common claims, the flex of a shaft has no effect on the club head speed, and there is little energy stored in the flex of the shaft that can be recovered at impact – this is all advertising BS. The shaft flex does however affect the loft of the club at impact. The huge (50 kg for a professional) tension in the shaft pulls at the heel of the clubhead. However, the centre of mass of the club head is a few inches away from the heel, near the centre of the head, and with a high swing speed the centre of mass tends to line up with the shaft. The shaft therefore bends towards the target and toe down a few centimeters. This effect provides club manufacturers with a way of expanding the range of lofts on their clubs. A flexible shaft will enhance loft by as much as 5 degrees, while a stiff shaft only about 2 degrees. Tip-stiff shafts also reduce this effect, and tip-flexible shafts emphasize it. Golfers with a slow swing speed require drivers with a high loft (14-15 degrees say) to achieve the greatest distance, whereas golfers with a high swing speed achieve optimum distances with a lower loft (as low as 9 degrees).


So there you have it! The great distances produced by good golfers using modern equipment are due to both technique and technology. The important factors we have discussed are:


Use the transfer of momentum and rotational energy from your turning body and arms to the clubhead and then to the ball. Don't try to impose your will on the club, but rather allow the energy to flow to it. (This is not some new-age proverb. As we saw, it is classical physics.) Particular techniques to use include:
  • Start the downswing with the club (and even the arms) "folded" close to the body.
  • Keep them folded there as late as you can into the downswing. That means the first part of the downswing is just rotation, with nothing from the hips up moving relative to any other part.
  • Do not apply wrist torque to swing the club out or forward into the ball. You may think you are increasing the clubhead speed with "hand action", but the physics shows that it does exactly the opposite.
Focusing on the mechanical aspects of technique, as we describe it above, is often unhelpful when you are playing. Our brains work better if we can establish an emotional connection to the correct swing. When you’re practicing at the range, practice by first swinging the club about your shoulders as though you are going to throw the club – don’t use your hands: remember how it feels, both the rhythm and the feel in your muscles. Now when you stand over the practice ball, remember the rhythm and feelings as you throw the club through the impact zone. When you hit a good shot, pause and enjoy it, and remember the feeling. Learn that feeling so you can recall it during your pre-shot routine on the course.


  • Clubhead speed is maximized by using the lightest, longest shaft you can control. But keep in mind the modern driver shafts are too long for the average golfer to swing without use of the hands, which means a tendency to lose control under mental pressure. Like some pros, you may find that backing off on the length and making sure of a consistent center-face impact is a better strategy for both average distance and control.
  • Modern drivers with the larger heads and flexible face have a higher Coefficient of Restitution than older drivers, and are a little more tolerant of off center hits. Update your driver if you have not already done so. If you already have a 460 cc driver, there is probably little to be gained.
  • Don’t be tempted by drivers with a low loft. The optimum loft for modern drivers with a low centre of mass and low spin rate, is a higher than for the older drivers. Few golfers need a loft below 10.5 degrees these days. Also, as your swing improves with less use of the hands, the less the club will be ahead of the hands at impact, and the lower the trajectory.
  • Don't worry excessively about clubhead weight. Choose it so you swing the club comfortably and consistently. Any commercially available driver head today is close enough to the mechanically optimum weight that you aren't losing any distance.

Last modified - Apr 10, 2010