1. Maximizing Distance
The optimal combination of ball speed, launch angle, and spin rate needed to maximize driving distance for a particular golfer are primarily dictated by the golfer’s club speed and attack angle.
The reason has to do with a tradeoff between ball speed, launch angle, and spin rate. Distance is maximized with a high ball speed, high launch angle, and low spin rate – however, increasing launch angle by increasing the dynamic loft has the side-effect of increasing spin rate and decreasing ball speed. So, a tradeoff must be made, and the optimal tradeoff depends on how an individual delivers the club to the ball. Maximizing ball speed also implies making center impact – or at least close to center impact – as well squaring up club path and face angle.
As an example, someone with a club speed of 90 mph and an attack angle of -5 degrees would maximize carry distance with a ball speed of 129 mph, launch angle of 11.1 degrees, and spin rate of 3690 rpm. Meanwhile, someone else with the same club speed of 90 mph, but an attack angle of +5 degrees would maximize carry distance with a ball speed of 132 mph, launch angle of 16.4 degrees, and spin rate of 2630 rpm. The golfer who hits up on the ball would end up with more carry: 214 versus 191 yards.
2. Smash Factor
Generally speaking, to maximize ball speed it is more important to improve centeredness of impact than to increase club speed.
An off-center impact is less efficient in transferring energy from the club to the ball, thus some of the power of the club speed is lost, resulting in a lower initial ball speed and consequently less carry distance. Smash factor describes the efficiency of impact and equals the ratio ball speed divided by club speed. Note that in addition to impact, the spin loft and club and ball properties also affect smash factor. This is important because it is common for amateurs to "over-swing". While over-swinging might increase club speed, it may negatively affect centeredness of impact, and net out in decreased ball speed, resulting in reduced carry distance.
As an example, assume someone with a club speed of 90 mph and smash factor of 1.45 can drive a ball so it has a carry of 200 yards. Increasing the club speed to 92 mph but reducing smash factor to 1.40 due to off center hit would result in a new carry of only 196 yards. Instead of increasing the club speed, the golfer could lower the club speed to 88 mph in order to swing under control and increase his or her impact, thereby increasing the smash factor to 1.50 resulting in a carry of 204 yards.
3. Spin Rate
Spin rate is generated primarily by spin loft and club speed; additionally, impact position and friction between the club and the ball (subject to a threshold) affect the amount of spin.
In general, a club with more loft generates more spin, up to the point where there is not enough friction to achieve “grip on the ball.” For iron shots, TrackMan has seen that spin loft (the difference between angle of attack and dynamic loft; SPIN LOFT = DYNAMIC LOFT – ANGLE OF ATTACK) remains virtually constant for a particular golfer, given club loft and club speed, no matter what the attack angle is. This means the myth that “hitting down on the ball creates more spin” is not true. For example, Moving the ball back in the stance generally creates a more negative attack angle, but the dynamic loft will be offset by a similar amount, resulting in an unchanged spin loft and thereby unchanged spin rate.
When impact is below center on the club face, more spin is generated, all else equal. Conversely, when impact is above center, less spin is generated, all else equal. This effect is pronounced on clubs where the center of gravity is significant behind the club face such as on drivers, woods and hybrids.
Reducing the friction below a certain threshold also reduces the spin rate. For example, if there is grass and/or water between the ball and the club, friction will be reduced,
and a low spin “flier” is a likely result.
Dynamic loft will have a greater influence than attack angle in determining the launch angle of a shot.
The initial launch angle of the ball always falls between the dynamic loft and attack angle at impact. TrackMan data has shown for drivers, that dynamic loft normally accounts for about 85% of the launch angle, while attack angle accounts for the remaining 15%. For irons, the ratio is around 75% dynamic loft and 25% attack angle. For example, a 10° launch angle would result from a iron shot where the attack angle is -5 degrees and the Dynamic Loft is +15 degrees (15 * 75% plus -5 * 25% equals 10).
When friction between the club and ball is too low to get “grip on the ball,” the launch angle will be even more weighted toward the dynamic loft. This explains why “fliers” carry more – they come out at a higher launch angle and with lower spin.
Note that the static club loft together with attack angle primarily determines the dynamic loft, but the “lead/lag” of the shaft and the club head position relative to the hands (also described by the left arm/shaft angle) also play a role.