Trucks can carry heavy load and when applying the brakes during for example a mountain downhill or for an abrupt stop, the brake temperatures can rise significantly. Elevated temperatures in the drum brake region can reduce the braking efficiency or can even cause the brake system to fail, catch fire or even break.It therefore needs to be designed such to be able to transfer the heat out of its system by convection, conduction and/or radiation. All three heat transfer modes play an important role since the drum brakes of trucks are not much exposed to external airflow, a significant difference from disk brakes of passenger cars analyzed in previous studies. This makes it a complex heat transfer problem which is not easy to understand. Numerical methods provide insight by visualization of the different heat transfer modes.Presented is a numerical method that simulates the transient heat transfer of a truck drum brake system cooldown at constant driving speed. A 3D CFD Lattice Boltzmann based solver, which calculates the convection, is 2-way coupled to a radiation and conduction calculation. The simulation includes real rotation of the wheels and uses 3D solid elements for the conduction. Simulation results are compared with experimental test results that were performed in the Tongji thermal wind tunnel in Shanghai. Due to the sufficiently large nozzle exit area this wind tunnel can provide realistic experimental data for trucks. Results obtained in simulation compare very nicely to the experimental data.