X X
X X
..Y
..Y
Rider "Y" can overlap wheels between riders "X" and "X" without too much risk because riders X can't go left/right without bumping into each other.
X X
X X
......Y
......Y
Rider Y can overlap wheels, but is risking a splat.
Gosh darn it spacing gets messed up.. So think of the periods as virtual spaces.