GP401 Mass Damper Set(Heavy) (Mini 4WD) Tamiya Grade Up Parts For boys From 15-year-old: Age good and fast shipping Amazing item for weight contron on your mini 4wd In the four wheel drive mini race, if there is a slope (uphill and downhill) is in its course, it will make it easier to off the track out of balance when landing after the vehicle body is to jump.