QA Explaining Swing Weight

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Editor's Note: This is the latest in a weekly Q&A feature from The Golf Channel's Chief Technical Advisor Frank Thomas. To submit a question for possible use in this column, email letsbefrank@thegolfchannel.com
 
Frank,
I've noticed that some drivers have different swing weights even with a shaft that weighs the same. Can you tell me how that works? -- Mark Bradley

 
Mark,
Swing weight is a measure of the counter balance required to be applied to the grip of the club when it is balanced at a fulcrum 14 inches from the end of the grip. This fulcrum distance was established as being the most appropriate one based on an attempt to quantify a weight matching system using Francis Ouimets clubs (U.S. Open champion 1913 as an amateur).
 
The concept was simple and assumed that every shaft in the set weighed about the same per inch of length, the grips all weighed the same and that the only two variables involved were shaft length and head weight. Based on this a method of matching was born called swing weight.
 
It is really not a dynamic measurement as the name implies but rather a simple balance system what in mechanics is called First Moments. This is where the distance of the weight from the fulcrum multiplied by the weight itself must be the same on both sides for the beam to balance.
 
In the case of swing weight the fulcrum has been pre-selected, as mentioned above, to be 14 inches from the butt end of the club. As times changed and shafts became lighter this changed the thinking a little.
 
The concentration of mass of the shaft i.e. the center of gravity or (c.g.) is close to the midpoint of the shaft length and is on the head side of the 14 inch fulcrum. For this reason with a lighter shaft i.e. Graphite vs. Steel the balance will be thrown off and more weight will need to be added to the head for the same swing weight to register on the scale.
 
(Visit franklygolf.com for the background on my invention of the graphite shaft)
 
So as you can see the swing weight is a simple balance beam and you can get two different swing weights in two different clubs with the same shaft weight but this would require adding or subtracting weight from the head.

Frank,
Years ago there was a English player named Paul Trevillion who used a short putter with a split grip, on short putts he would hold the right hand around six inches above the ground and move it upwards as the putts got longer. Its said he made a 1000 four foot putts and never missed a putt, also he would take anyone on in a putt-off, and never lost. Why is it no PGA pros have ever used his method, least wise that Ive seen? -- Joe Cody

 
Joe,
This is being done every day but with a modified putter which will do about the same thing. Not quite as well but without the back breaking stance. The long putter is one similar in concept to the one you describe. The idea is to eliminate as many variables and sources of error in the putting stroke as possible. The low right hand exaggerated split grip short putter eliminates at least three degrees of freedom or at least minimizes them to being almost ineffective and so minimizes the potential of these influencing the stroke. These degrees of freedom are:
 
a) The up and down motion (raising the head of the putter off the ground to various heights as the left arm is firmly lock in place and hand or wrist becomes a pivot point).
 
b) The rotation of the wrists as these are no longer in play.
 
c) The wrist break as opposed to a firm left wrist. Breaking the left wrist seems to be the cause of many misses.
 
With these three degrees of freedom out of play you are left with only the two side ways movements across the line of the putt and along the line of putt. The action of the right hand for the short putter is a bowling move which is better than that used on the long putter which is across the body and not natural. There is no doubt that this style of putting is excellent for short putts as proven by Sam Snead.
 
Frank,
I recently made my annual pilgrimage to the local golf emporium to compare this years hot new drivers and put the manufacturers claims to the test on the launch monitor. My driving distance is usually 250-270 yards, as confirmed by my Skygolf GPS, which has a shot distance function. However, the launch monitors always seem to dock me about 50 yards, giving me readings of around 200-220 yards (carry plus roll), even when hitting my own driver which I know I hit 250+.

This is a recurring pattern regardless of the launch monitor Im using. My favorite golf shop is equipped with TaylorMades MATT system, Callaways proprietary fitting system and their own non-proprietary system. All three show spin-rate, launch angle, club head speed, ball speed, distance, etc. And they all seem to uniformly low-ball me about 50 yards.

As the prime technical guru of the golf universe, do you have any ideas as to why this might be? -- Amir Stark

 
Amir,
I think I must first say that most of the launch monitors predict the distances based on a preset formula taking launch angle spin rate and ball speed as the input variables. They also use a standard turf condition (producing about 25 yards of roll for a standard drive) and the aerodynamic properties of a generic ball. This is not bad for general use. It will certainly get the golfer into the right ball park for club selection to approach, as close as they can, the Optimum Conditions. The lower the head speed the lower the ball speed and the higher the launch angle is needed. Also as the ball speed goes down so must the spin rate go up. Check the link franklygolf.com to get the numbers.
 
In your case a difference of 50 yards between your measured drives and the launch monitors predictions seems to be off the mark somewhere. If this is, as you say, consistent across the board then the only thing I can conclude is that your actual measurements should be checked and you must also be experiencing an unusual ball roll condition.
 
I would like to be more positive about this but know that most launch monitors are reasonably close to what golfers find based on some very good research. Your case is an anomaly and when you analyze the conditions under which you play and make your measurements you may find the reason for these differences. Let me know when you do.
 
Frank,
I'm writing about a frustration I have had for quite sometime and that is reference to topspin in golf shots other than putts. I can't give you a specific example but if you are like me (and my assumption of the notion of topspin full shots is correct) I am sure you have made note of them as well. Frequently, folks talk about hot clubs or shots that have topspin and role out a long away as a result. Could you first confirm that no normally hit shot with any club other than perhaps a putter (and even them most times there is backspin with that club too) that topspin is both not desired and would be a quite rare phenomenon.
 
I am not a physicist but I believe backspin is what creates lift in a golf ball, along with the dimples of course, and contributes to length of carry. Excessive backspin of course produces more lift than desired generating a flight path that diminishes overall length, as there would be less or sometimes no roll out. Focus now is on optimal backspin along with launch angle and initial velocity to create the most carry and roll out.
 
Am I correct? -- Gary Marx

 
Gary,
You are right. Every ball is hit with back spin, even a putt which is minimal but it does have back spin unless struck with an upward stroke which takes a lot of talent (see The Anatomy of a Putt at franklygolf.com where you can see exactly what happens. Dont be fooled into believing otherwise.
 
For all other shots the only way a ball can stay in the air for any length of time is for it to have a lift force equivalent to or greater than the weight of the ball (the force being applied by gravity). The dimples on the ball create a rough surface creating a turbulent layer of air which believe it or not decrease the resisting drag force after about 50 mph and also, because of the back spin create an airfoil section similar to an aircraft wing. This creates the lift forces, a result of a higher pressure on the underside of the ball than the top side.
 
A ball with top spin may cover a distance of about 35 yards in the air compared to 250 yards in the air with a similarly struck ball with back spin.
 
Frank Thomas, inventor of the graphite shaft, is founder of Frankly Golf, a company dedicated to Helping Golfers. Frank is Chief Technical Advisor to The Golf Channel and Golf Digest. He served as Technical Director of the USGA for 26 years and directed the development of the GHIN System and introduced the Stimpmeter to the world of golf. To email a question for possible use in an upcoming Let's Be Frank column, please email letsbefrank@thegolfchannel.com