How Spin Really Happens

Introduction: Spin is Not Just a Number

Spin is often treated as a basic launch monitor output, just another figure on the screen. But beneath that number lies a complex interplay of physics, material science, and biomechanical variables. Understanding how spin is generated, and what influences it, is critical for club fitters, coaches, and players seeking consistent, high-level performance.

Despite its importance, spin generation remains poorly understood, often oversimplified as a function of loft and friction. In reality, spin results from nuanced physical interactions between the clubface and the golf ball, particularly during the sliding and rolling phases of impact. This article unpacks those interactions, introduces key concepts like Spin Coefficient of Restitution (SCofR) and overspin, and explores how environmental factors such as moisture can further complicate spin generation.

By improving our understanding of these mechanisms, we lay the foundation for more precise coaching, fitting, and equipment design. A follow-up article will explore how different golf ball types influence spin in applied settings.

Understanding Spin: More Than Just Friction

Many golfers, and even some fitters, tend to associate spin generation solely with friction between the clubface and the golf ball. While friction certainly plays a role in helping the ball grip the face, it is only one part of the equation. Spin is fundamentally tied to how energy is transferred during impact—particularly how that energy is divided between translational (linear) motion and rotational (spin) motion.

To understand how spin truly occurs, it’s helpful to explore the phases of impact described by Cochran and Stobbs in The Search for the Perfect Swing. They outline two distinct phases:

1. Sliding Phase: When a lofted club strikes the ball, it initially slides upward across the clubface and is slightly compressed. Friction between the ball and the face begins to act during this phase, starting the process of spin generation (Cochran & Stobbs, 1968).

2. Rolling Phase: As friction takes hold more completely, the ball transitions from sliding to rolling. At the moment the ball stops sliding entirely and rolls purely, it reaches its maximum spin rate. From that point until separation, spin rate typically decreases until the ball leaves the clubface.

The Role of Overspin and Spin Coefficient of Restitution (SCofR)

Dewhurst (2015) adds detail to the work of Cochran & Stobbs by introducing the concept of overspin, a phenomenon that occurs when the rotational speed of the ball exceeds what would be expected when only considering sliding and rolling in isolation.

This leads us to the Spin Coefficient of Restitution (SCofR), a relatively underexplored but vital concept. SCofR is a measure of how much rotational energy a ball retains as it leaves the clubface. Just as Coefficient of Restitution (CoR) measures energy transfer for ball speed, SCofR addresses how much spin is retained or lost during impact.

During impact, the ball initially deforms and slides along the clubface. Dewhurst (2015), in his chapter on the mechanism of overspin creation, explains this using a spring model. He describes how the ball behaves as if it contains two internal springs, one compressing perpendicular to the clubface and another parallel to it. As the ball flattens against the face and begins to grip, shear forces apply torque to the ball, forcing material at the top of the contact point to enter the surface while material at the bottom exits more slowly. This creates a pressure imbalance across the contact zone, with higher pressure and friction where material is entering, and lower pressure where it exits. As the ball starts to separate from the face, the release of this stored energy causes the surface to slip at its lowest contact point, initiating rapid spin. If this slip occurs late in the contact phase, more strain energy is converted into spin, contributing to overspin. If the slip happens too early or too late, less energy is available for spin generation, reducing the SCofR.

Factors that influence SCofR include:

• Ball construction and layering

• Cover material (urethane vs. ionomer)

• Surface texture of the clubface (grooves, milling)

• Spin loft (dynamic loft minus angle of attack)

• Friction coefficient at impact

A ball that maintains a high SCofR through its design will deliver more spin under appropriate conditions. For coaches and fitters, understanding this principle is essential for making targeted interventions, especially in areas such as wedge fitting, approach play, and adapting setups for course and weather conditions.

Yet, the spin potential of any given shot is rarely realised under perfect circumstances. Environmental factors, particularly moisture and surface interference from grass, can disrupt the phases of impact and alter how energy is stored and released. These effects are especially pronounced with higher lofted clubs, where the disruption to frictional engagement can significantly reduce spin.

Recognising how real-world playing conditions diverge from controlled indoor testing environments is crucial. Coaches and fitters must account for these variables when interpreting data, selecting equipment, or designing player interventions.

Moisture, Loft, and Spin Reduction:

Environmental conditions can interfere with spin generation, especially when moisture is present. Using a ball cannon to simulate club–ball collisions at different lofts and speeds, Lieberman (1990a, as cited in Dewhurst, 2015) explored how “grassy” or wet conditions affect spin production.

Their results illustrate that spin rates in dry conditions rise with loft and speed. However, when moisture is introduced, this relationship becomes non-linear. At higher lofts, moisture acts as a lubricant that reduces friction, leading to a significant drop in spin generation and typically causing an increase in launch angle. Dewhurst (2015) notes that this effect is more pronounced with higher lofted clubs, where the spin loss can be substantial. For example, at 55 degrees of loft, dry conditions produced approximately 14,000 rpm of spin, whereas under wet conditions this dropped to around 7,000 rpm, a 50% reduction. This striking difference highlights how sensitive spin generation is to environmental changes and reinforces the need to account for these variables when evaluating performance.

Interestingly, at lower lofts (e.g., 20–30 degrees), the presence of moisture between the clubface and ball can sometimes lead to an increase in spin. This occurs because the ball initially slides for longer, unable to grip the face immediately. As the water is displaced and friction builds, the extended sliding phase can allow a late but sharp increase in rotational energy, resulting in a temporary spike in spin. This phenomenon defies the conventional assumption that moisture universally reduces spin.

These findings demonstrate several key points:

• Moisture acts as a lubricant, reducing the friction needed to transition from sliding to rolling.

• The relationship between loft and spin is non-linear, especially in wet conditions. Higher lofts, typically expected to produce more spin, can suffer disproportionately.

• Spin loss is more severe with higher lofted clubs under moist conditions, making wedge and short iron performance more vulnerable to environmental interference.

• Lower lofted clubs may outperform expectations in terms of spin when conditions are wet or when small amounts of grass interfere with the interaction between the club and ball, which has implications for both approach play and club selection strategy.

Conclusion

These outcomes underscore the need for coaches and fitters to reassess performance expectations and adapt fitting protocols to consider real-world application. A 50% reduction in spin, as seen with a 55-degree wedge under wet conditions, demonstrates just how significantly launch and spin characteristics can change in the real world. Indoor testing environments may produce clean, consistent data, but without accounting for environmental variables such as grass, water, or debris, this data may not reflect what actually happens on the course. By understanding how loft, moisture, and friction interact, and how these interactions affect spin, coaches, fitters and players can make better-informed decisions, offer more reliable guidance, and ultimately enhance performance under a broader range of conditions.

References

Broadie, M., Koenig, R. & Neal, R., 2010. Accounting for ball performance differences in golf club fitting. Procedia Engineering, 2(2), pp.3241–3246.

Cochran, A. & Stobbs, J., 1968. The Search for the Perfect Swing. London: Heinemann.

Dewhurst, P., 2015. The Science of the Perfect Swing. Oxford: Oxford University Press.

Lieberman, D., 1990a. Experimental research on ball spin generation, in Dewhurst, P. (2015). The Science of the Perfect Swing. Oxford: Oxford University Press.

The R&A and USGA, 2007. Second Report on the Study of Spin Generation. St Andrews: The R&A.

Tugwood, R., 2025. 'X-rated models uncovered: Why Titleist’s Pro V1x is no longer the hottest ball in the business', Today's Golfer. [Online]