Minecraft wiki entry for Minecarts, associated text: There is also a difference in unmanned (empty) or storage minecarts, so a shorter interval is needed if these carts are expected on the track. The optimal pattern to make storage minecarts move quickly is 3:1 (1 powered rail every 4th block). Compared to shorter intervals, the reduction in speed is minimal. The widest possible interval seems to be 8:1 (power every 9th block) -- any longer, and the minecart does not reliably reach its destination. In practice, 7:1 may be better, as an 8:1 pattern will have empty carts coming nearly to a stop between the powered rails, and will fail given any interference whatsoever.