Road unevenness induces longitudinal as well as vertical forces in the suspension. The variation of vertical and longitudinal wheel forces can be of the same magnitude. Much work on vertical loads has been accomplished in heavy vehicle development, but less on longitudinal forces. Wheel forces have been measured on a semi-trailer tractor driven over a test track obstacle. The consistency of test results inspires confidence in the measured loads. Measured forces are compared with results from a simple simulation model. The influence of road-induced longitudinal forces on ride and chassis loads is demonstrated through simulations. The importance of longitudinal suspension compliance is discussed.