 Since the drive sprocket can be at either the front (M4 Sherman, many other WWII tanks) or the rear (T-90, most modern tanks) of the vehicle depending on the design, the idler wheel either carries the track back off the ground and returns it to the drive sprocket (rear idler wheel), or receives track from the drive sprocket and lays it down in front of the road wheels (front idler wheel).The idler wheel is not powered, just like an idler gear.Although it technically reverses the tracks direction (but not its "rotation"), this has nothing to do with the term "idler"; it is not related to an idler gear other than that they are both "idle", or not doing any work, only transmitting power ("idle" being a term for something or someone who isn't working).