  Artin-Tits groups act on a certain delta-hyperbolic complex, called the
"additional length complex". For an element of the group, acting loxodromically
on this complex is a property analogous to the property of being pseudo-Anosov
for elements of mapping class groups. By analogy with a well-known conjecture
about mapping class groups, we conjecture that "most" elements of Artin-Tits
groups act loxodromically. More precisely, in the Cayley graph of a subgroup
$G$ of an Artin-Tits group, the proportion of loxodromically acting elements in
a ball of large radius should tend to one as the radius tends to infinity. In
this paper, we give a condition guaranteeing that this proportion stays away
from zero. This condition is satisfied e.g. for Artin-Tits groups of spherical
type, their pure subgroups and some of their commutator subgroups.
