In micro particle suspensions many different forces act between the particles. For accurate simulations of such suspensions, it is essential to consider the contact forces between the particles and the fluid and the normal and tangential contact forces between the particles themselves. Current simulation methods, such as coupled CFD-DEM simulations, often do not consider all forces, limiting the ability to fully represent the rheological behaviour of suspensions. To address this issue, we investigated the effect of different forces on the rheology of the suspensions. We found that a contact model, a static friction model, a rolling friction model, a drag model, a rotational drag model and a lubrication model are all required to accurately describe the rheological properties of micro particle suspensions. The contact model and static friction models must be included to account for direct particle contact. Rolling friction is essential to represent the non-spherical shape of the particles [1]. Drag forces influence the velocity of the particles, while rotational drag forces keep the particles rotating. Rotational drag is generally only considered directly in resolved simulations, but should also be used for accurate unresolved simulations [2]. Lubrication forces are necessary to account for the displacement of fluid between particles and dissipate energy within the suspension [3]. In addition, a combination of electrostatic, steric and van der Waals forces are required to account for colloidal suspensions [4]. To validate the simulations, we conducted experiments with spherical and crushed glass in silicone oil and with cement and limestone in a water-cellulose mixture, to account for sedimentation. Our simulations using the described forces show good agreement with analytical models and experimental data over a broad range of volume fractions.