The computer-aided simulation of dynamic systems requires a mathematical model of the real system and an excitation model (incl. corresponding excitation signal) to adequately describe the interface of the dynamic system to the external environment.
In the context of vehicle simulation, the tire model together with a digital road profile is the typical excitation model used. Another approach would be to excite the vehicle directly using the measured wheel hub forces and moments, in other words, doing without the road profile and tire model.
Tire model and road profile
However, between these two approaches there is a major difference: Together, the tire model and the road profile define a so called invariant excitation model, i.e., the excitation does not depend on the simulated system - the vehicle model - but rather can be used to simulate different vehicle options (with the same tires). However, measured wheel hub forces and moments very much depend on the measured vehicle having a suitable vehicle type; they are not invariant, but are rather system dependent and can only be used to excite a model of the measured vehicle.
Invariant excitation models are very desirable in terms of cost and effort, measured drives with many vehicle variants are expensive and time consuming. On the other hand, the appropriate invariant models are often not available.