Impact Location, Spin Loft, and Smash Factor: An Analysis Using Golfer-Club Systems and TrackMan 4 Data

Abstract

Smash factor is commonly used to describe energy-transfer efficiency between the golf club and ball, but it can be influenced by multiple aspects of club delivery and impact. This study examined how much unique variation in seven-iron smash factor was associated with spin loft and with two-dimensional impact location in eight individual golfer-club systems. Eight experienced right-handed male golfers were tested using a TrackMan 4 launch monitor. Each subject was tested indoors, using their personal seven-iron. 767 total shots were used in this study. Smash factor was treated as the dependent variable, while spin loft and impact location were the two predictors studied. Face angle was included as a control variable. Impact location was represented using a two-dimensional model of the second order, containing the terms x, y, x², xy, and y². Separate models were created for each golfer-club system. The unique contributions of spin loft and 2D impact location were measured as the decrease in R² when each predictor was removed from the full model. Across the eight golfer-club systems, impact location contributed greater explanatory information than spin loft, with a median unique ΔR² of 0.586. Spin loft’s median ΔR² was 0.025. Five-fold cross-validation was used to evaluate predictive performance; cross-validated R² remained positive in every system, with a median of 0.529. These results suggest that preserving the direction of impact location retains important explanatory information when studying smash factor and that the relative importance of strike location and spin loft can vary across golfer–club systems.