Several studies have investigated the robustness of the soundaction perception to auditory delay, and the effects of delay on performance in tapping gesture. In this paper we propose a complementary approach, by modifying the stiffness of the tapped object. Participants had to perform synchronous tapping along with a metronome reference, using a one degree-of-freedom haptic device. Two experimental conditions were tested: with and without sound from the tapped object. Dynamics of the experiment were recorded in order to examine the dynamic factors affecting performance. Results show that the increase of the stiffness of the tapped object leaded to a decrease of the asynchrony, indicating that the modification of the interaction force has an effect on performance. On the basis of this observation, an explanation of the negative asynchrony effect is proposed. At last, we show that sound feedback improves performance only when the stiffness of the tapped object is very low.