  An exact macroscopic extended model for ultrarelativistic gases, with an
arbitrary number of moments, is present in the literature. Here we exploit
equations determining wave speeds for that model. We find interesting results;
for example, the whole system for their determination can be divided into
independent subsystems and some, but not all, wave speeds are expressed by
rational numbers. Moreover, the extraordinary property that these wave speeds
for the macroscopic model are the same of those in the kinetic model, is
proved.
