This study compares the performances of six different commercial viscosity index improver additives for manual gear box lubricants. They have different chemistries and molecular masses and are blended in a mineral and a hydrotreated base stock. They are considered for their viscometric properties, their mechanical shear stability, and their low temperature behaviour by dynamic viscosity measurements in presence of suitable pour point depressants. When an extreme-pressure package is added, the influence of these polymer additives on oxidation stability is also discussed. It appears that these different performances can be interpreted according to different polymer characteristics like molecular masses, chemical structures, or dispersant properties.