{TAIL ~ Bicycle drive unit} capable of backward movement and naughtrotation and {HEAD ~ forward movement} traveling when rectitude or reverse pedaling 
{ TAIL ~ Bicycle drive unit } capable of backward movement and naughtrotation and { HEAD ~ forward movement } traveling when rectitude or reverse pedaling
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH