Minecraft wiki entry for Minecarts, associated text: An optimal use requires the synchronization of minecart movement and powered rail placement; moving a powered rail a single block forward or back along a track can make a significant difference. This is because the momentum of a minecart is increased per tick (=1/20 of a second) the cart spends on a powered rail (by 0.9 m/s for occupied carts). When a cart travels at the maximum 8 m/s on a straight track, it alternately spends either 2 or 3 ticks on each block. For optimal placement, the powered rail must be put where the cart spends 3 ticks, otherwise, one-third of the boost is wasted.