Vertical Gear Effect

Vertical gear effect describes what happens when contact is above or below the clubface's vertical center of gravity. When the ball is struck high on the face (above center), the clubhead twists slightly at impact. That adds extra backspin and raises launch angle beyond what the loft and attack angle alone would produce. This is the mechanism behind skied and popped-up shots. There, too much height and backspin combine with reduced ball speed to produce a short, weak result.

When the ball is struck low on the face (below center), the opposite happens. Vertical gear effect reduces backspin and can lower launch angle. Sometimes that produces a flat, low, "knuckling" ball flight that is hard to predict in the air. Very low spin rates make a ball flight more sensitive to small variations in dimple pattern and airflow. This is part of why a thin or bladed shot often produces a low, boring flight. It can sometimes fly surprisingly far in calm conditions, but it is uneven and hard to control, especially into wind.

Driver fitting makes deliberate use of vertical gear effect. Modern drivers are often designed and fit with attention to where a golfer's typical strike lands vertically on the face. A golfer who tends to strike slightly low can benefit from a driver and setup tuned to add a bit of extra backspin. That avoids an overly flat, low-spin ball flight that can lose stability. A golfer who strikes high may need a setup that reduces the spin vertical gear effect would otherwise add.