The purpose of this study was to examine the effects and relationships of selected musical variables on the horizontal (i.e., successive eighth note timing relationships) and vertical (i.e., the degree of ensemble synchronicity between separate parts) timing properties of jazz rhythm. A total of 949 eighth note samples from five improvised solos by saxophonist Chris Potter were analysed. Musical variables included metrical beat placement, melodic character, intervals, articulation, underlying harmony, and tempo. Results of the simultaneous multiple regression analyses revealed that intervals preceding and intervals succeeding the sample eighth notes had a significant effect on eighth note durations. Articulation had a significant effect on upbeat beat ratio. The relationships between the relative onset timing data of the saxophone, bass, and drums yielded significant results. There was a large, negative correlation between the relative timing onsets of saxophone and bass, a large negative correlation between saxophone and drums, and a moderate, negative correlation between bass and drums. Implications for the fields of music education, pedagogy, and cognitive psychology are discussed.