The SINGLE most direct measure of a putter’s resistance to twisting is MOI
Cleveland Golf introduced their Frontline Putters in September 2019, making claims of a revolutionary new approach to forgiveness that depended on face milling and moving the center of gravity forward nearer the face, discounting the value of MOI. Even promoting the idea that MOI is dead… Ludicrous.
A putter’s moment of inertia (MOI) is its resistance to twisting. Claims of increased stability that are not reflected in MOI are marketing gibberish.
The nut of their claim is that they can restore the distance lost on toe and heel mishits by means of face milling; without depending on MOI at all. It works, sort of. Cleveland calls their version of the face milling Speed Optimized Face Technology (SOFT). Ping has a similar milling pattern that they call TruRoll.
Both of them work on the same principle. The aggressive milling at the center of the face “deadens” the face there, while the smoother face to the toe and heel remain lively (the extreme toe and heel of the Ping pattern is not involved in ball face contact). Cleveland provides data in a published paper documenting about a 6.3% deadening of the of the center hit. Ping’s results would be similar.
The physics of the ball face interaction at impact includes a significant variation likely related to the dimple effect or at least groove/dimple interactions. Note the variation in roll-out in the Cleveland results from about 2.3 to 2.4 meters (about a 4% variation) – this would be about 15” for a 30’ putt.
Traditional answer style putters like the Newport 2 have a parabolic distribution of roll-out results. The CURE RX5 high MOI putter reduces roll-out variation simply by adding MOI without the variation of center deadening.
The goal of the Cleveland Speed Optimized Face Technology was to flatten the decay in roll out exhibited by low MOI putters like the Newport 2. The resulting pattern is technically “flatter” but is also “FATTER” creating a large and unnecessary variation in distance control that defeats the purpose of the design itself.
CURE achieves a better, flatter result by maximizing MOI. The results with high MOI have less face angle variation and less putter twist at impact.
Increasing MOI with weight optimized fitting improves putter speed variation as an additional benefit along with reducing face angle variation (see 8/3/19 Science Dude Blog on Weight Optimization Fitting). Reports of the death of MOI have been greatly exaggerated.
The Dwell Time of the Ball on the Face of a Putter
The ball is on the face of a putter for a very short time, only about 0.00043 seconds (just under one half of one thousandth of a second). The dwell time can be extended (a little) by a softer ball, softer putter face, or by an aggressive milling pattern on the putter face (including grooves).
Putter Face Twist at Impact in the first one half of a thousandth of a second
All putters twist at impact with an off-center impact. The putter head twists around its center of gravity (COG) until it is restrained by the shaft. The putter continues to twist for well over one thousandth of a second; continuing to twist long after the ball has left the face. Moment of inertia (MOI) is the measure of the putters’ physical resistance to twisting. A low MOI putter will twist more than a high MOI putter from the same off-center impact with the ball.
Quintic Ball Roll Labs USA testing demonstrated that a traditional anser style blade putter with a MOI of about 4000 gcm2 will twist near a full degree on a 0.5” off-center hit; while a high MOI mallet with a MOI of about 11,400 gcm2 twisted only 0.15 degrees. The traditional answer style blade twisted about 600% as much as the extreme high MOI mallet. MOI resists twisting at impact, period!
Reports of the death of MOI have been greatly exaggerated.
Ball Exit Angle from Twist at Impact (away from the intended line)
The ball will leave the putter face on an angle associated with the twist from an off-center impact. A toe hit will push the putt to the right; a heel hit will pull the putt to the left. The geometry involved is simple angle of incidence and angle of reflection; like a billiard ball bouncing off the rail at angle similar to the angle at which it contacted the rail.
All putters twist around the COG of the putter (the red dot above) at impact on an off-center hit regardless of where the COG is placed.
Ball Speed Loss from Twist at Impact
Energy is consumed in the twisting of the putter head in addition to sending the ball off-line. Less energy is transmitted to the ball on the intended line if the putter is twisted by an off-center impact. The measurement of this energy loss is impact ratio (ball speed divided by putter speed).
Quintic Ball Roll Labs USA testing demonstrated that a traditional answer style blade putter with an MOI of about 4000 gcm2 with a center-hit impact ratio of 1.70 will decay to between 1.53 and 1.62 on a 0.5” off-center hit; while a high MOI mallet with a MOI of about 11,400 gcm2 with a center-hit impact ratio of 1.70 will decay only to 1.68 or 1.69. The traditional anwser style blade would lose over 3 FEET on a 30’ putt where the extreme high MOI mallet would only lose only about 2 INCHES. Remember, variable face milling varies distance 15” on a 30’ putt without human variation in putter speed, this is NOT control. MOI resists twisting at impact and maintains impact ratio (distance control), period!
Reports of the death of MOI have been greatly exaggerated.
Gear Effect Spin (the dirty little secret of deep mallets)
Gear effect spin is created by the interaction between the ball and face of the putter. The lateral displacement of the contact point while the face is in contact with the ball causes the ball to spin. The diagrams below exaggerate the twist of the putter head dramatically to demonstrate the principle.
The rearward location of the COG on larger four-corners weighted mallets necessarily increases gear effect spin on off-center hits. Moving the COG forward will reduce gear effect spin; but increasing MOI has a much stronger influence on gear effect spin by dramatically reducing the twist itself. As discussed already; conventional putters with a MOI of approximately 4,000 gcm2 twist about 600% more than high MOI putters such as the Cure RX1 with a MOI of 11,400 gcm2 . Cure putters employ a forward COG design as well as industry leading high MOI to directly resist the rotation and reduce gear effect.
Forward COG with high MOI is the REAL answer to combating gear effect spin without sacrificing distance or line control. Reports of the death of MOI have been greatly exaggerated.
Excess Ball Exit Angle from Gear Effect Spin (a very bad bounce)
The gear effect spin on putts behaves very differently from gear effect spin on woods. Hook spin from a toe hit on a wood draws back (in the air) to the intended line of the shot. The same hook spin from a toe hit on a putter (on the green) behaves like right English on a billiard ball and curves to the right. In the case of a putt it essentially jumps or bounces to the right because the spin is largely consumed in the initial contact with the ground.
The initial bounce to the right (on toe-hit putts) adds to the exit angle simply from the twist at impact discussed above. And the excess exit angle from gear effect spin appears to be on the order of 5 times greater than the twist.
Quintic Ball Roll Labs testing showed that mid mallet putter twisted about 0.25 degrees during impact with the ball (about 0.00043 seconds) but the exit angle of the ball was a whopping 1.25 degrees offline (5 times the twist at impact). The excess exit angle can be explained by gear effect spin.
Moment of Inertia is the most powerful influence on putter performance regarding ALL of these issues: A higher MOI putter resists twisting at impact; a higher MOI putter has much more consistent impact ratio over the entire face; a higher MOI putter will dramatically reduce gear effect spin excess exit angle.
Reports of the death of MOI have been greatly exaggerated.
When a ball is struck by a putter it does not immediately begin to roll. It may be launched into the air and bounce a few times, with rolling motion added with every bounce. It may skid along the ground several inches while the friction with the green surface induces rolling motion. It achieves true pure roll when the entire circumference of the ball remains in contact with the green with no skidding. This skid phase generally takes only a few inches and amounts to between 10% and 20% of the entire length of the putt. For discussion purposes we will assume that the skid phase is about 15% of the putt length.
A 10’ putt will skid about 1.5’. The ball will leave the putter face at about 5 mph with the putter head traveling at about 3 mph at impact. The 5 mph ball speed divided by the 3 mph putter speed equals an impact ratio of about 1.7 (this is the “smash factor” if you have a driver in your hands in the fitting bay).
At the end of the skid phase the ball is rolling at about 3 mph and rolling at 600 rpm (revolutions per minute). That is to most, a surprisingly high rpm. The ball doesn’t “want” to roll, it requires a lot of energy to get the ball rolling. From the moment the ball is struck and energy from the putter head imparted to the ball the friction of the green’s surface relentlessly slows the ball to a stop. You can see the energy change in the diagram below. 2 mph of forward speed is “transformed” into rolling energy. To create an “instant” initial roll the ball would need just over 700 rpm (shown to the left of the diagram below).
It is possible to impart a small amount of backspin, on the order of 50 to 100 rpm, at impact from a lofted putter and/or negative attack angle (hitting down on the ball). It is possible to impart a small amount of topspin, similarly on the order of 50 to 100 rpm, at impact from a low effective loft or positive attack angle (hitting up on the ball). It is simply NOT POSSIBLE to impart anything like the 700 rpm of topspin required to impart true pure roll at impact.
The topspin deficit is substantial on the 10’ putt above; on the 40’ putt below the topspin deficit becomes overwhelming.
Several manufacturers have claimed to be adding 25 to 50 rpm of top spin by using proprietary face or groove design. My guess is they can add 25 rpm to a 10’ putt and 50 rpm to a 40’ putt. Neither is going to make a very big change in the behavior of the ball on the green.
A bigger improvement in topspin can be made from decreasing the effective loft of the putter to between zero and two degrees and decreasing the attack angle (hitting the ball with a slightly upward stroke). As much as 100 rpm can be added to a 10’ putt and even more to a 40’ putt.
The biggest influence on topspin comes from loft and attack angle.
Reducing skid by adding topspin turns out to be a fool’s errand. Much more important is the variability of the skid distance from erratic launch angle and spin. Skid distance variation range is the most important launch monitor metric related to topspin and skid; and adding topspin does not improve this metric, if the spin and other metrics are erratic.
The surest way to decrease skid distance variation range is to increase the MOI of your putter and optimize your putter head weight.
More importantly, numerous launch monitor variables can be improved dramatically simply by increasing the MOI of your putter and using a putter weight optimized for you as an individual.
The following variables are ALL improved with MOI and Weight Optimization Fitting:
face angle variation range, putter speed variation range; launch angle variation range; attack angle variation range; skid variation range; initial ball roll variation range; side spin variation range.
The ball is 1.68” in diameter. The circumference is πD (3.1416 x 1.68 = 5.28”) or 0.440 feet. Revolutions per minute (rpm) is speed in feet per minute divided by 0.440 feet per revolution. 1 mph = 5280 feet per hour; or 88 feet per minute. This 88 ft/min divided by 0.44 feet per revolution = 200.73 rpm per mph (rounded to 200 rpm per mph in the examples above).
The ball leaves the bottom of a stimpmeter at 4.09 mph (1.83 m/sec) and is therefore rolling at 821 rpm. There is no skid with a stimpmeter (except on the incline), on the green there is only true pure roll.
If the ball is launched into the air by a lofted putter and/or extreme positive attack angle, even if the initial spin is backspin, the first contact with the ground produces a lot of forward spin, topspin. And more spin is added by each subsequent bounce until the ball is at a true pure roll.
Several years ago RIFE introduced their 2 bar blade and claimed that their patented groove design was improving roll dramatically. The biggest difference in their putters however was not their grooves; the biggest difference was their loft. RIFE putters had a loft of 2° when the competition was at 4° or more.
Our launch monitor testing confirms that a 2° lofted putter produces much more topspin than a 4° lofted putter. The average loft of CURE putters is 2°; ranging from 1.5° to 2.5°.
Independent testing at the Quintic Ball Lab USA in Massachusetts confirmed the importance of MOI, moment of inertia, resistance to twisting. Quintic Ball Roll Lab USA in a second phase of testing explored the impact of the utilization of the extreme weight range allowed by the Cure RX Series putter. In this human (no more robots) testing we discovered the surprising benefit of weight optimization fitting.
The alpha test was with a 16 handicap golfer; an average putter for his handicap with a 2.9o face angle variation range in his baseline putter test. 9 Cure RX Series putter configurations were tested. Face angle variation range decreased (improved) in the first 5 tests; and then failed to improve more in the last 4 tests. The putters in tests 1-5 “felt” good to the player; the putters in tests 6-9 “felt” too heavy to the player. An OPTIMUM WEIGHT was discovered at 409 grams for this player.
The alpha test discovered an optimum weight outside the industry expectation (as indicated by the average weight of available putters) of between 345g and 355g. Improvement in a number of putter launch metrics was noted, including importantly: putter speed variation range, launch angle range, and zero skid range.
The beta test was with a 6 handicap golfer; a relatively poor putter for his handicap with a 2.1o face angle variation range in his baseline putter test. 9 Cure RX Series putter configurations were tested. Face angle variation range decreased (improved) in the first 2 tests; and then failed to improve more in the last 4 tests. The putters in tests 1-4 “felt” good to the player; the putters in tests 5-9 “felt” too heavy to the player. An OPTIMUM WEIGHT was discovered at 395 grams for this player.
The optimum weight for face angle variation range and putter speed variation range coincided at the same weights; with the same pattern: improvement up to the optimum weight and then no further improvement.
Subsequent tests have been done with players of all skill levels including PGA Tour players, PGA Tour Champions players, LPGA Tour players, web.com and mini Tour players, International Tour players and amateurs from +4 handicap to -32 handicap. The results persistently confirm an optimum weight for players of all skill levels a putter weight heavier than generally available in the market.
The results are GAME CHANGING!
Average players can improve their putting to tour caliber without a putting lesson. Simply put a weight optimized, MOI maximized putter in their hands and their putting launch monitor metrics improve, a lot!
This is scientific proof that each player has an optimum weight, individually determinable.
The formula for MOI, moment of inertia, is mass (g) times distance (cm) squared. So you can increase MOI a little by increasing the mass; but a lot by increasing the distance of the mass from the axis of rotation. MOI divided by mass is radius of gyration squared (k2). This is a very simple calculation; and allows a direct measure of the effectiveness of the mass distribution in generating MOI.
The Scottsdale anser was an important improvement over the old blades; 19% more k2 (9.43/7.92) than the old blade. The Newport 2 was another important improvement; 30% more k2 (12.34/9.43) than the original anser style blade. But there is a limit to the improvement possible in the traditional geometry using the heavy steel base material. Steel weighs about 7.92 g/cm3
The CURE TX1 develops 40% more k2 (17.41/12.34) than the Newport 2 by using lightweight aircraft grade aluminum as a base material. The aluminum weighs only 2.72 g/cm3 (and feels great!). By using tungsten weights in the toe and heel, the TX1 develops the MOI of a large high mallet in a blade.
The CURE RX5 uses the same aircraft grade aluminum but in a 6” wide putter; developing levels of MOI, STABILITY and forgiveness never before seen.
The modern putter evolved from very light wooden shafted wooden head putters with 10 or more degrees of loft (sometimes a lot more than 10 degrees). Many golfers would carry two “putters”; one with about 10 degrees of loft for putting very near the hole itself; and a second, with 12 to 15 degrees of loft, for putting from distances of 30, 50 or even 80 yards from the hole.
Greens in the 19th century were cut with scythes to a height that would be similar to our fairways and tees today. The invention of the lawn mower in 1830 by Edwin Budding in England enabled important changes in golf course maintenance.
Historical Green Speeds in the USA
By the early 20th century, putting greens were being mowed to 3/8” in height.
By the end of the roaring 20’s, green mowers had developed into specialized equipment, and mowing heights were a little tighter. Putter loft began to decrease; but the Calamity Jane putter used by Bobby Jones to win his Grand Slam in 1930 still had 8 degrees of loft. Between 1930 and 1980, greens steadily improved; but the “fast” greens of today still did not exist.
The Stimpmeter, invented by Eddie Stimpson, was used by the USGA in 1977 to measure 581 courses nationwide to benchmark the speed of American greens. Here is a sampling of what was found:
These were America’s finest courses; the averages courses and “muni’s” were more typically in the range of 4 to 6 feet.
While the loft of putters began to decrease as the mowing height on the greens was reduced and green speeds increased, the loft of standard putters remained quite high.
Green Speed, Cut Height and Putter Weight Evolution
The steady decrease in mowing height and loft, and the increase in green speed and putter weight is
evident in the table below:
The Myth of the Nested Ball
It has for many years been “common knowledge” that some loft is required on a putter to lift the ball out of the depression in the grass that it was sitting in. This was likely true for Bobby Jones, Ben Hogan and Arnold Palmer; but is no longer true today.
A famous putter designer in his current putter fitting guide states that his “Putter Studio research shows that a ball pushes down slightly into the grass on a green, and that 3.5o loft is needed to lift the ball up and on to the surface for a smooth roll.” He is not alone. This statement could have been made by any of hundreds of top teachers.
But the ball is no longer sitting in a deep depression in the grass on a putting green today.
In addition to the evidence from historical developments on the putting green, new research is pointing toward lower loft.
The growing use of launch monitor metrics has confirmed that less loft, higher weight and higher MOI are more consistent on today’s faster greens.
The growing use of launch monitor metrics has revolutionized club fitting. Woods & irons today are routinely fit on the basis of launch monitor metrics: launch angle and direction, spin rate, smash factor, carry distance and club twist at impact.
The use of putting launch monitors is not yet as widespread, but is growing. The single most important putter launch monitor metric is face angle variation. The face can be closed, square or open at impact. In the example below the face angle variation range is 2.0o (1.0o closed to 1.0o open). Even in the “stopped- frame” view below, one degree is not easy to see. In real time it very hard to see.
Face angle is the overwhelming determiner of the direction of the ball. Stroke path is much less important.
Face angle variation can be reduced by increasing the MOI, moment of inertia, of your putter. Putting launch monitor testing has confirmed that high MOI putters can reduce face angle variation range by 50%, or more! While this fact is not yet widely known, the growing use of putting launch monitors will confirm this game changing fact.
Increasing the MOI, moment of inertia, of your putter makes it more STABLE; and this added STABILITY is reflected in decreased face angle variation. This is physics; and this is a game changer!
Independent testing at the Quintic Ball Lab USA in Massachusetts confirmed the importance of MOI, moment of inertia, resistance to twisting. STABILITY, forgiveness and MOI are clearly related.
The results shown below were obtained on a state-of-the-art robot. An traditional anser style putter was tested against a high MOI Cure RX Series putter: first, with a center hit; and then second, with a 1⁄2” off- center hit.
Figure 1 (above) shows the comparison of the center hit and off-center lab test results. Both the traditional anser style putter (top) and the high MOI Cure RX Series putter (bottom) performed well on the center hit (left side), with 0.0o twist and a 1.70 impact ratio.
The off-center hit (right side of figure 1 above) exposed the weakness of the traditional blade putter and the strength of the high MOI putter. The anser style putter twisted 6 times as much as the high MOI putter at impact. SIX TIMES as much; 1.00o vs 0.15o of twist at impact. Putter twist at impact will send the ball off line. The actual directional result is quite complicated, but twisting is not helpful.
Impact Ratio is the ball speed divided by the putter speed at impact. The ball in this case was going 1.70 times as fast as the putter head. 1.70 is a relatively common impact ratio for putters. You may be more familiar with the concept of Smash Factor with your driver or irons. Smash Factor and Impact Ratio are EXACTLY the same number (ball speed divided by club speed). It is not helpful that the industry is using two terms for exactly the same thing. Both could be called Impact Ratio, but that is not going to happen. Smashing, think KABOOM!, works with drives; putting is more delicate and precise, so get used to impact ratio on the green.
The off-center impact resulted in a reduction of impact ratio. Less of the forward energy of the putter head is transferred to the ball. The anser style putter deteriorated from 1.70 to 1.52 on the off-center hit, enough to cause the putt to come up over 3 FEET short. The high MOI putter only deteriorated from 1.70 to 1.69, almost nothing at all, causing the putt to come up only about 2 INCHES shorter. So a high MOI putter improves BOTH the DIRECTION and DISTANCE resulting from an off-center hit.
Increased MOI, increased resistance to twisting, increased STABILITY, increased forgiveness, improve putting performance. This is physics. Higher MOI produces measurable improvement and forgiveness.