NewsLetter info
#2
How Weight Adjustments Affect Ball Flight
It’s not a secret that one of the trends in clubhead design that has gained momentum over the past years, and will undoubtedly
increase in consumer demand through 2011, are drivers created to allow weight movement around the head as a means of
correcting golfer ball flight problems. What this means is that clubmakers will be asked questions by golfers about how such
weighting modifications actually change the ball’s flight. Because TWGT knows it’s important for clubmakers to be there with
the right answers, the following information will help you explain to your customers how moving weight around a clubhead
brings about this change. There are a number of these options but now I will look at just one, and maybe the most popular.
Draw Bias Weighting

The term “bias” has been used in conjunction with weight distribution to connote the ability to move weight around a clubhead
to create more of a tendency, or a bias, to a specific direction of ball flight. Hence “draw bias” weighting is when more mass
is placed on the heel side of the clubhead to reduce a slice/fade, and in turn enhance the golfer’s ability to draw the ball more
than with a clubhead designed with “neutral weighting.”
Putting more mass in the heel side of the clubhead reduces the tendency to fade the ball in two ways:
1.        By reducing the Moment of Inertia (MOI) of the head about the shaft axis or hosel. There are two important MOI’s in the
clubhead. First, the MOI about the axis of the Center of Gravity (CG) of the head, and second, the MOI about the axis of the
hosel bore, i.e. the shaft centerline. MOI about the CG of the head has to do with allowing the head to be “more forgiving” from
an off-center hit. MOI about the shaft has to do with the golfer’s ability to rotate the entire head back to square during the
downswing, before impact with the ball. Thus by adding more weight to the heel area of the clubhead, the MOI of the head is
reduced, which makes it easier for the golfer to rotate the head from open to square or possibly even more closed, before the
clubhead makes impact with the ball. For a person who slices the ball, adding weight to the heel allows them to deliver the
club face less open and thus help reduce the amount of slice or fade on the ball. (see fig. 1)


























2.         By changing the “gear effect” of the head in response to impact with the ball. As you know, the “gear effect” describes
the way the ball is able to pick up more “hooking” sidespin when impact occurs toward the toe side of the CG position of the
head. If the golfer makes contact on the toe side of the CG position in the head, the head will respond by immediately
beginning to rotate clockwise around its CG (clockwise for a RH head, and counter clockwise for a LH head, but the effect is
the same). In this split second of head rotation while the ball is on the face, the head rotation will cause the ball to slide and roll
toward the hosel. That movement of the ball across the face causes the ball to pick up more of a tilting of the axis of backspin
rotation in a hooking direction. Thus by moving greater mass toward the heel of the head, the CG is usually moved in that
direction as well which causes the golfer to be able to hit the ball in the center of the face and still receive this “gear effect” of
slightly more hooking sidespin to reduce their amount of fade or slice. (see fig. 2)
 

Precision Club-Making
Grant James, NZPGA AGCP
8 Komiatum St, Holsworthy 2173
NSW, Australia
phone; 02 8064 7573
cell; 04 3597 0177
golfdoctor@bigpond.com