This study evaluates the negative effects of grip wax application on the dynamic ski–snow coefficient of friction and subsequent performance during the double poling cycle in cross-country skiing. Utilising a linear ski tribometer, friction tests were performed on classic cross-country skiing skis prepared with no, thin, and thick grip wax under controlled laboratory conditions. The dynamic coefficient of friction was estimated under various load conditions, reflecting dynamic skiing motions. Results indicated a clear increase in coefficient of friction with the addition of grip wax, with significant differences observed between thin and thick applications. Specifically, compared to skis with no wax, the coefficient of friction for skis with thin and thick wax layers experienced a negative increased by 1.8% and 3.2% during double poling, and by 1.7% and 2.6% whilst gliding, respectively. These friction increases were associated with higher power requirements during skiing or a consequent time loss. This underscores the need for meticulous application of grip wax application, tailored to the snow conditions, ski camber profile and racecourse demands, to minimise impact on gliding performance whilst maintaining sufficient static coefficient of friction for effective use of the diagonal stride technique. Furthermore, the skier should utilise a skiing technique to minimise the risk of encountering load conditions that increase the coefficient of friction. Overall, this research provides quantitative insights into the trade-offs between grip enhancement and friction-related performance losses in cross-country skiing.