A car with underinflated tires can lead to both safety and environmental issues. To combat this, markets have begun requiring new cars to feature a Tire Pressure Monitoring System. Systems without pressure sensors are referred to as indirect Tire Pressure Monitoring Systems, often utilizing wheel speed sensors in combination with other available sensor information to detect tire pressure losses.  NIRA Dynamics is a company founded in Linköping, Sweden, most known for its indirect Tire Pressure Monitoring System called TPI. TPI needs to be verified in a large number of scenarios, which may be both difficult and expensive to realize in real vehicle tests. The purpose of this master thesis was to investigate and model what physical phenomena are associated with having a trailer connected to a car, relevant for TPI. The goal was to construct a hybrid simulation framework, making it possible to modify car-only data to reflect the effects of having a trailer connected.  A car-trailer model was developed, showing close resemblance in simulations to real collected car-trailer sensor data. The model was then used to design a hybrid simulation framework, where car-only sensor signals were modified to mimic having different types of trailers attached. The hybrid simulation results show close resemblance to real collected trailer sensor data. By not requiring real trailer data for every scenario to evaluate software performance on, the proposed framework opens up the possibility to simulate data from a much larger number of trailer combinations than would otherwise have been feasible to test in real vehicle tests.