Use of a mixture of a complex ester with a monocarboxylic acid to reduce friction

A fuel additive, comprising,

• (I) at least one complex ester obtained by an esterification reaction of:
• (A) at least one aliphatic linear or branched C2- to C12-dicarboxylic acid,
• (B) at least one aliphatic linear or branched polyhydroxy alcohol with 3 to 6 hydroxyl groups, and
• (C) a chain stopping agent comprising:
• (C1) at least one aliphatic linear or branched C1- to C30-mono carboxylic acid in case of an excess of the component (B), or
• (C2) at least one aliphatic linear or branched monobasic C1- to C30-alcohol in case of an excess of the component (A);
• and
• (II) at least one aliphatic monocarboxylic acid having from 12 to 30 carbon atoms, wherein:
• a weight ratio of the complex ester (I) to the aliphatic monocarboxylic acid (II) is from 20 to 80:80 to 20;
• and
• the fuel additive is adapted to function as an additive in a fuel for reducing fuel consumption in the operation of an internal combustion engine.