Real-time simulation is a valuable tool in the design and test of vehicles and vehicle parts, mainly when interfacing with hardware modules working at a given rate, as in hardware-in-the-loop testing. Real-time operating-systems (RTOS) are designed for minimizing the latency of critical operations such as interrupt dispatch, task switch or inter-process communication (IPC). General-purpose operating-systems (GPOS), instead, are designed for maximizing throughput in heavy-load systems. In complex simulations where the amount of work to do in one step is high, achieving real-time depends not only in the latency of the event starting the step, but also on the capacity of the system for computing one step in the available time. While it is demonstrated that RTOS present lower latencies than GPOS, the choice is not clear when maximizing throughput is also critical.In this paper, the performance of RTOS and GPOS running complex real-time simulations is compared, focusing on the computation of large simulation steps. GNU/Linux has been chosen as GPOS. A RTOS is chosen with a micro-benchmark comparing the major choices of Linux-based RTOS. Once chosen the systems, the simulation of a tire model is used as application case for benchmarking, comparing within 52470 different configurations (with different number of elements and threads). The benchmark measures which configurations miss a single deadline, and demonstrates that even in simulations with a high number of elements and large time steps, RTOS are a better choice due mainly to the latency associated to IPC and task switch when the simulation is parallelized.