In the common use of tractors and other self-propelled machinery, drivers are subject to high levels of vibrations, primarily due to the dynamic stress from travelling on rough surfaces. To mitigate the transfer of vibrations, modern tractors are often equipped with comprehensive suspension systems, including devices fitted on the front axle, the cab (platform) and the seat. For a long time, mechanical or pneumatic suspension of the driver’s seat has represented the only means to reduce the level of vibration experienced by the operator. To ensure proper damping, the suspension usually includes a stiffness adjustment, typically referred to the driver's mass, ranging from 50 to 130 kg. Unfortunately, in practice, this adjustment is often neglected or overlooked, which reduces or completely nullifies the beneficial effects of the suspension. This study aims to analyze the level of vibrations transmitted to the operator when driving a tractor on uneven surfaces with incorrect suspension adjustment. A mid-range tractor equipped with a mechanically suspended seat was tested on a farm road in fairly good condition at increasing speeds, considering both correct and significantly incorrect adjustments of the suspension (softest and hardest settings). As expected, except for one condition, incorrect adjustments resulted in higher vibration levels. The obtained data were compared with the limits established by the relevant standards. Considering the vibrations on the vertical (Z) axis only, the levels frequently exceeded the provided limits, posing a significant risk to the long-term well-being of the operator.