Minecraft wiki entry for Minecart_with_Furnace, associated text: A furnace minecart can be made to pull up to four other minecarts. All minecarts in this train move at the constant speed of the furnace minecart. Trains are formed when a minecart is pushed into the back of a powered furnace minecart or a short-enough train. These shunts are fragile at best and easily come undone, but some methods are stronger than others. For example, pushing a minecart into a furnace minecart and then powering the furnace gives a weaker shunt than pushing the furnace minecart into the other minecart against a wall, and then powering the furnace in the other direction.