MIG wrote:

Also, even on a
non-circular line like the Central, that would mean that the north side
got more worn out, because of the way it bends and so on. I wonder if
it's really a problem?

Unbalanced wheel wear was seen as a potential problem for the
Eurotunnel shuttles, which is why the turning loop at the French end
has the opposite sense to the one at Folkestone. Whether that was
based on actual evidence I don't know.

Peter CS