More than 20 million people worldwide rely on wheelchairs as their primary source of mobility. One American database reveals an average of 51.3 deaths per year from wheelchair accidents, with almost 37,000 persons annually seeking treatment in emergency rooms after such incidents. The purpose of this study was to determine if caster type, speed or bump height affect the tendency to slip out of or tip in the wheelchair while crossing surface obstructions. Nine participants were used for this study-four were experienced wheelchair athletes and five were non-wheelchair users. Participants used an Action Pro-T lightweight manual wheelchair for the study, equipped with standard (ST) front wheel casters and Frog Leggs[Registered trade mark symbol] (FL) shock-absorbing casters. Two steel bumps (1.2 cm and 1.8 cm high) were attached to a force platform and two impact velocities were tested (1.6 and 2.0 m/s). Each subject performed five trials in each of the eight conditions. In order to assess the potential for slipping out of the chair, the peak anterior/posterior ground reaction force was measured. Increases in this variable indicate that there is a greater likelihood of slipping out of the chair when the bump is contacted. There was a 48.8% reduction when using the FL caster, a 22.5% increase at the faster speed and a 45.0% increase at the higher height. In order to assess the potential for tipping over, the magnitude and direction (angle) of the force vector was measured. Increases in magnitude and decreases in angle indicate a greater likelihood of tipping. The FL decreased the magnitude by 43.0% and the angle by 22.3%. This combination of magnitude and direction allowed the rear wheel to remain in contact with the ground more often using the FL caster (83.2%) than the ST caster (22.9%). The faster speed increased the angle by 2.6%. The increased bump height increased the angle by 23.6%. These results indicate that the caster was safer than the ST caster, especially crossing the high bump. Also, there appears to be a threshold speed that is safer to cross the high bump with greater momentum.