Comfortable leg splay of mid-sized males in automotive seats

Many factors affect the comfort of automotive seats including pressure distribution, vibration, temperature, and backrest inclination. However, one aspect of seating that has not been well studied is leg splay; splay is a rotation at the hips which causes the knees to move outward. The work presented here identified the ranges of "comfortable" splay in different styles of seats and related changes in seating pressure due to leg splay. Sixteen midsized male participants were tested in six seats: a flat control, three mid-sized sedan, a sports car, and a pickup truck. Participants sat with two leg conditions: 1) shoulder width apart and 2) rotating their legs to splay to a self-identified, comfortable position. For each test, the participant placed his left leg on a foot support and right leg on a depressible pedal to mimic a driving position. In each posture, leg angle and seat pan pressures were collected. Of the seats tested, the flat wooden seat had the highest possible splay (24.5°). The three sedan seats had similar splay angles (16.1-18.5°). The lowest splay values were in the sports car seat (8.96°) and truck seat (7.46°). This reduction in splay was attributed to the more aggressive bolsters in the sports car and a higher seat design position in the pickup truck seat. Following participant splay the pressures in the seat bolsters increased while the pressure in the left thigh and left buttocks regions decreased. By determining the comfortable ranges of splay and how pressure distribution is affected, seat designers and automobile manufacturers can use these data when evaluating seat designs and occupant positioning.