  As part of the European Supernova Collaboration we obtained extensive
photometry and spectroscopy of the type Ia SN 2002dj covering epochs from 11
days before to nearly two years after maximum. Detailed optical and
near-infrared observations show that this object belongs to the class of the
high-velocity gradient events as indicated by Si, S and Ca lines. The light
curve shape and velocity evolution of SN 2002dj appear to be nearly identical
to SN 2002bo. The only significant difference is observed in the optical to
near-IR colours and a reduced spectral emission beyond 6500 A. For
high-velocity gradient Type Ia supernovae, we tentatively identify a faster
rise to maximum, a more pronounced inflection in the V and R light curves after
maximum and a brighter, slower declining late-time B light curve as common
photometric properties of this class of objects. They also seem to be
characterized by a different colour and colour evolution with respect to
``normal'' SNe Ia. The usual light curve shape parameters do not distinguish
these events. Stronger, more blueshifted absorption features of
intermediate-mass elements and lower temperatures are the most prominent
spectroscopic features of Type Ia supernovae displaying high velocity
gradients. It appears that these events burn more intermediate-mass elements in
the outer layers. Possible connections to the metallicity of the progenitor
star are explored.
