TAMIYA HIGH SPEED EX GEAR SET - MS CHASSIS / GEAR RATIO 3.7:1 There are currently two gear ratios available for Mini 4WD racers to use on their MS chassis machines, 4:1 and 3.5:1. This means that for a particular circuit sometimes the former may be too slow while the latter may be too fast. To solve this situation and give racers another option, this new set offers a 3.7:1 ratio gear set.