Nowadays, lumbar supports are applied when designing tractor seats to address the issue of tractor operators’ lumbar discomfort. This research aimed to investigate the effect of lumbar support on ride comfort using various lumbar support thicknesses and running velocities based on body pressure distribution measures and subjective comfort evaluations. The repeated measures ANOVA results revealed that the lumbar support thickness (p < 0.05) and running velocity (p < 0.05) had a prominent, main effect on the pressure distribution indexes, and the interaction effect between them was also significant (p < 0.05). As the lumbar support thickness increased, the degree of comfort at the waist, thigh, elbow, and for the overall body first increased and then decreased, while shoulder comfort was reduced continuously. There was an obvious relationship between the outcome of the subjective comfort assessment and the pressure distribution indexes. The 3 cm thick lumbar support did not enhance ride comfort significantly, whereas the 9 cm thick lumbar support imposed excessive pressure on the lumbar spine, thus leading to an excessive forward inclination of the lumbar spine and increased tiredness. Most tractor operators selected the 6 cm thick lumbar support. This research provides insights from practical applications that may be useful for the design and assessment of tractor seats, based on body pressure distribution, to increase overall ride comfort and reduce operator fatigue.