Effective communication between driver and horse via rein signals is essential for safety and horse welfare. Good driveability should at best reflect the absence of unnecessary harsh equipment. Yet, many trotters suffer from mouth lesions but associations with equipment, rein tension and motion patterns are currently unclear. Our project aims to define optimal driveability in dialogue with drivers via interviews and questionnaires. We also aim to categorize equipment used at competitions and associations with horse behaviour. Finally, we will test selected equipment under experimental conditions in terms of rein tension applied, horses’ reactions to it and effects on motion patterns. Results will serve as a solid base for informed discussions with representatives in the harness racing industry. Through education of the effects of equipment on rein tension, behaviour, and locomotion, horse welfare and health can be safeguarded and accidents prevented.