Use as lubricants, especially for tractive drives, of ester compounds of the general formula I
wherein Cb denotes a carboxylic grouping which may be monocarboxylic (MCb) of formula -O-CO- or -CO-O-, dicarboxylic (DiCb) of formula -O-CO-R₄-CO-O- or -CO-O-R₄-O-CO-, or tetracarboxylic (TCb) of formula -O-CO-R₅-CO-O-R₆-O-CO-R₅-CO-O-; R₄ represents an optionally substituted alkylene or alkenylene group, a C 5-10 cycloalkylene group, a di-(C 5-10 cycloalkylene) group, or a C 5-10 cycloalkenylene group; R₅ represents an alkylene group and R₆ represents a cycloalkylene group;
each group R₃ individually represents a C 1-6 alkyl, C 2-6 alkenyl, C 3-20 mono- or polycycloalkyl group or a hydrogen atom; m and n are each 0 or 1;
R₁ represents an optionally substituted C 4-10 tertiary alkyl group or an optionally substituted C 3-8 cycloalkyl or C 6-14 bicyclo or tricycloalkyl group; and R₂ represents the same as R₁ or alternatively represents an optionally substituted alkyl, alkenyl, mono- or polycycloalkyl, mono or polycycloalkenyl group; provided that when m and n are each 0 and Cb is MCb or DCb wherein R₄ is cyclohexylene, then R₁ and R₂ are not both cyclohexyl.