This article is an excerpt from a book I wrote with Jim McLean entitled, The Ultimate Guide to TrackMan Swing Analysis. For more information about purchasing the book, click here.
Are you a TrackMan user? Check out the color feedback app I developed with TrackMan. The app provides color feedback and tips on 5 key TrackMan parameters to help you quickly interpret the data and improve your numbers.
Gear effect is a term used to describe why hitting the ball off center will alter the ball flight. When contact is made anywhere but the sweet spot, it causes the club face to change its orientation. During that brief moment, the ball and club are trapped like two gears, and the ball moves (or gears) in the opposite direction of the club face. This is how gear effect alters the SPIN AXIS. The following examines gear effect’s influence on ball flight curve when contact is made on the toe or heel.
Trackman research published in 2009 compares a 6 iron with a driver when contact is made 1 dimple (0.14”) off center and ½” off center. Below is a summary of the findings assuming a square FACE TO PATH:
Looking at the data, you can see gear effect increasing its effect on the SPIN AXIS the further contact is made off center. From 1 dimple to ½” off center, the SPIN AXIS increased by 14 degrees with a driver and 5 degrees with a 6 iron. These statistics from Trackman should make you take gear effect more seriously!
To illustrate this concept, when contact is made on the toe with a driver, the CG swings to the left of the target line (downward in the 2D illustration). As the CG moves left, the ball gears in the same direction (to the left). The opposite is true with heel contact and this is how gear effect changes the ball’s SPIN AXIS.
Another factor is how far off center contact is made. The more off-center, the more gear effect will influence the SPIN AXIS. When the club head’s CG is located further behind the leading edge, it adds more twisting of the club head at impact, which makes the ball gear to a greater degree. The diagram below shows each club head’s estimated CG and its distance from the leading edge.
As you can see, each club has a CG behind the leading edge, which means every club will experience some level of gear effect. However, woods and drivers have the CG far enough behind the leading edge to produce a very noticeable effect on the SPIN AXIS. It happens because the CG “swings” to a greater degree when contact is off-center, and that movement causes the ball to gear.
To eliminate the influence of gear effect, you must learn your impact pattern with impact tape, or spray. Identifying a common impact pattern will help you make the appropriate adjustment and prevent working on the wrong things. For example, if you’re slicing the ball, let’s say 35 yards to the right, this may entice you to practice a more closed club face or a path more from the inside. But, if you’re using impact spray and learn your impact pattern is roughly 1/2” toward the heel, you now know this is a primary cause of your slice so you do not have to practice a more closed club face or a path from the inside, You need to work on fundamentals that produce solid contact. I’ve outline these fundamentals in the book, The Ultimate Guide To TrackMan Swing Analysis and the Pure Drive Golf App (available on the Apple Store). These adjustments will help you move your impact pattern closer to the center so you can eliminate the influence of gear effect and have greater control of your ball flight curve.