What is the difference between sliding 5th wheel and sliding kingpin? The purpose of the sliding 5th wheel and sliding kingpin is to allow for a more generous turning radius when you get into a tight spot. They accomplish this in two different ways. On the sliding 5th wheel set up, the 5th wheel slides approximately 16”. ON the sliding kingpin set up, the kingpin does the sliding. The kingpin can be set in three different locations. All the way closed, in the middle, or all the way open.