Bit late i know, but i had the same problem. After externsive testing and bloodpressure rise, results:
it doesnt matter where you place the wheels, as long as they are not angled on the X (nose-tail) axis.
Depending on which surface you place them on, they might not be parallel to the axis in which case,
symmetry building makes them face slightly towards (or away from) each other, with wobbly results.
However, I want to place my wheels where i want to and not only on X parallel surfaces.
Cure: Draw a mental axis from the nose to the tail of the plane and use the rotate tool (summetry on)
on one of the wheels. You need to make sure that the Orange axis on the rotate sphere is parallel to your
nose-tail axis. Your wheels should now have 0 degree angle between them, meaning they are both
pointing straight - forward.