Using greases offers numerous advantages to the railroad system, which include the lifespan extension of wheels and rails, fuel consumption decrease, and the reduction of the friction coefficient and component wear. However, there is still a lack of understanding regarding the relationship between the grease formulation and its performance. This study aims to investigate the impact of grease viscosity and thickener on its ability to reduce wear. Thus, a series of tests were conducted using a twin disc tribometer. Four greases were tested, formulated with an identical additive package and base oil and varying viscosities (50 cSt and 500 cSt) and thickeners (calcium and lithium). The results indicated that the lithium-thickened greases performed better than the calcium ones due to lower mass losses and crack depths, smaller plastically deformed subsurface layers, and higher retentivity. Additionally, the findings revealed that the lower (50 cSt) viscosity showed superior performances also due to lower mass losses and crack depths. However, the higher viscosity exhibited higher retentivity compared to the 50 cSt greases.