The Importance of the Strike Point on the Club Face

What causes a golf ball to curve in the air?

Generally speaking if there's a difference between the club path and club face aim at impact then the ball will curve in the air. For example if the club face is open to the path the ball curves from left to right and if the face is closed to the path the ball curves from right to left.

The starting point of the shot is determined by the both the face aim at impact and the club path, with the face aim having a greater influence (approx 70/30 face aim/club path). The curvature is then determined by the difference in the face aim and club path as well as the difference between the angle of attack and the launch angle(spin loft).

However there is one impact factor that can skew the expect results i.e. centeredness of strike.

Let's look at two similar shots recorded on TrackMan last year to see what can happen with two different strike points on a driver.

Shot	Club Speed (mph)	Angle of Attack	Club Path	Face to Path	Ball Speed (mph)	Launch Angle	Spin Rate (rpm)	Carry (yards)	Distance to Target (feet)	Spin Axis
A	102.5	1.8	-2.1	-1.1	152.4	13.9	2437	253.2	103.5 L	-9.1
B	102.7	-0.3	-2.2	-0.5	153.2	14.2	3075	268.2	34.8 R	7.3

So looking at the club path and the face to the path in both shot A and B, both values are negative meaning both are going to the left of the target. As a result we would expect both shots to start left of the target and to curve right to left away from the target but shot B finishes right of the target (34.8 feet right) and shot A finishes a long way left of the target (103.5 L). We would also expect that the curvature wouldn't be that much as the difference between the face and the path isn't great (1.1 and 0.5 degrees). So both shots should start left of target and curve just a slight bit more.

So what happened? The factor that gives us an idea is Spin Axis, if the spin axis is minus the ball is moving right to left and positive moving left to right. Shot A has a spin axis of -9.1, much higher than the path and face to path would suggest. Shot B has a spin axis of 7.3, higher and is positive when expecting a negative value.

So what caused this to happen? The strike point on shot A was on the toe and the strike point on shot B was on the heel. There is a gear effect with the driver, toe shots curve right to left and heel shots curve left to right. This is caused by the clubface rotating around it's center of gravity on off center strikes.

Here's a link to Brian Manzella's forum with a discussion on gear effect.

http://www.brianmanzella.com/golfing-discussions/14569-off-center-gear-effect-driver-impact-affects-d-plane.html

Also note that there is little gear effect in irons.

What does this mean for you?

Just be wary of your strike point before analysing your swing. These two swings were quite similar but gave wildly different results (138.3 feet apart!!). Also, as we see in shot B an out to in path with a closed clubface can still lead to a left to right shot. Generally some would suggest closing the clubface to cure a slice but this wouldn't work in shot B.

Also a swing and strike that would cause a result like shot B with a driver would end up left with an iron.