Analyzing Ball Impact Wear Spot
by: Ralph Maltby - Founder of The GolfWorks
Tour players hit the ball better than any of us. It's their job and they hit a lot of golf balls almost every day. One aspect of tour players' clubs that has always amazed me is the wear spots tour players generate on the faces of their clubs. Regarding irons, the wear spot is a slight oval and not much bigger than the compression size of the golf ball at impact.
It is important to completely understand the dynamics of the wear spot location with respect to a specific iron design. The wear spot location explains the playability of that design and furthers the understanding of the mass and dimensional properties that apply to the Maltby Playability Factor
Golf has had an uncanny tendency to generate myth. I don't know how many times I have heard that better players strike the ball toward the heel and not in the center of the face. Magazines still write this stuff. Some club designers still tout it. They pick it up from some other guy who wrote about it last year and that guy picked it up somewhere else. It goes on and on, and the myth is perpetuated. I can tell you how it started, because it was during my early days.
It seems that in the 1950s, '60s and '70s, golf experts noticed that the wear spots on most Tour players iron faces were in the heel, so they concluded that all the good players strike the ball in the heel. Well, it turns out that most (not all) manufacturers of this era designed irons without regard to center of gravity location and it usually ended up in the heel area. This occurred because they were designing clubs the traditional way with longer hosels, shorter blade lengths, relatively narrow soles and, of course, many irons of this era were muscle back forgings.
The truth of the matter is that tour players strike the ball where the impact feels the most solid. This applies the maximum force to the golf ball resulting in best distance, best trajectory and maximum backspin. Two basic conditions must first occur for the impact to feel most solid. First, the ball must be struck in-line with the horizontal center of gravity (CG) location. Secondly, the ball must be struck with the clubhead's actual vertical center of gravity (AVCOG) being driven (force path vector) equal to, or slightly lower than, the golf ball's center of gravity.
Ed Sneed, multiple winner on the PGA Tour and a friend of mine, gave me the three sets of Ben Hogan irons. Ed played a number of regular PGA Tour events with the 1974 Director irons and the 1979 Forged Apex irons. The 1996 GCD Tour Edge irons were played exclusively on the Champions Tour. Ed hit enough balls to generate very specific and visual wear spot areas that were very easy to measure in both the vertical and horizontal axis.
Look at the drawings to the right closely and first note the location of the actual centers of gravity horizontally (Drawings in A.) The wear spot in all cases is located almost exactly on the horizontal CG. Note also that between the 1979 Forged Apex iron and the 1996 GCD Edge iron there is almost a 5/16" variance between horizontal CG locations.
Regardless of this difference, Ed still impacted the ball on the horizontal CG of each different iron design, because this is where the iron felt the most solid to him and performed the best.
The slight oval in the heel to toe direction occurs because the impact location horizontally varied slightly. Analyzing all three 5 irons, relating to their horizontal CG location, Ed varied his impact location horizontally by less than 1/8" inch. I am sure that on occasion he hit it worse than this, but it was so infrequent that it did not increase the wear spot size.
Next, note the vertical CG impact location shown in Drawing B to the right. The actual vertical CG of the ironhead is always below the golf ball's CG at impact. All three heads yielded the same result. This is also necessary for a solid hit. Remember also, that Ed hit down and through the ball to some degree that produced an ironhead force path vector at impact that would actually drive the CG even lower than is shown in the static position in the drawings.
This explanation and drawings show conclusively that mass and its dimensional properties within a clubhead are significant characteristics in hitting a golf ball solidly. Also, it shows that tour pros have the ability to find this spot wherever it is located on any type of clubhead design.
A very important point to make here is that very few of us can hit balls with the precision of a tour professional and certainly do not have the ability to search out and find the exact center of gravity location. Most golfers need a higher playability factor (MPF) that gives them wider more forgiving areas to impact the ball horizontally (wider sweet spots) and lower centers of gravity to make sure that the clubheads CG at impact is always below that of the golf ball's (gets the ball in the air more easily and is more solid) regardless whether a golfer sweeps through the ball, hits up on it or hits down on it with a descending arc.
How Playability Factor Is Measured
Geometric Center Of Clubface:
First, the clubhead is measured to determine the Geometric Center of the face, where the face centerline is. Then, the Center of Gravity (C. of G.) is identified by measuring in two planes — up the clubhead in a vertical position, and across the horizontal plane of the clubface. Then the location of the C. of G. is compared to the Geometric Center of the face and other reference points, as follow:
Vertical Center of Gravity:
The distance from the C. of G. of the clubhead to the groundline.
- Lower Vertical C. of G. = More Consistent Trajectory
- Lower Vertical C. of G. = More Solid Hits
- Lower Vertical C. of G. = HIGHER PLAYABILITY FACTOR
Horizontal Center of Gravity Dimension:
The distance from where a vertical line dropped from the C. of G. of the clubhead intersects the groundline from the point where the centerline of the hosel intersects the groundline.
- Greater Horizontal C. of G. = Larger Sweet spot
- Greater Horizontal C. of G. = More Solid Hits
- Greater Horizontal C. of G. = HIGHER PLAYABILITY FACTOR
Rearward Center of Gravity:
The distance from the C. of G. of the clubhead to the centerline of the hosel, measured front to back with the centerline of the hosel in a vertical position.
- More Rearward C. of G. = Slightly Higher Trajectory With The Same Loft
- More Forward C. of G. = Slightly Lower Trajectory With The Same Loft
Moment of Inertia (M.O.I.):
The tendency of the clubhead to resist twisting around its C. of G. in the heel-toe direction (a function of how much the total mass is distributed away from the center of gravity, towards the heel and toe).
- Greater M.O.I. = More Distance On Off-Center Hits
- Greater M.O.I. = More Solid Feel On Off-Center Hits
- Greater M.O.I. = Better Directional Control On Off-Center Hits
- Greater M.O.I. = HIGHER PLAYABILITY FACTOR