The goal of this study is to determine the effect of amplitude and frequency of force sinusoids on force perception of the foot, in order to design an effective haptic feedback system for gas pedals. Eight subjects were asked to push a gas pedal to a constant workpoint position against a background force of 25 N. Force perception was determined for three frequencies and three types of footwear by requiring subjects to respond with 'yes' or 'no' after each force sinusoid. Psychometric functions were calculated from the data, relating the ratio of yes answers (averaged over all subjects) to the amplitude of the force sinusoid. Although large standard deviations were found for low ratios, a statistically significant just noticeable difference (JND) could be determined for the upper boundary of perception. Increasing the frequency of the stimulus decreased the JND. Footwear was shown to have a substantial impact on the JND at all frequencies, the largest effect occurring at the lowest frequency.