  Results from 2.5D and 3D studies of the onset and development of the tearing
instability are presented, using high fidelity resistive MHD simulations. A
limited parameter study of the strength of the reconnecting field (or shear
angle) was performed. An initially simple 1D equilibrium was used, consisting
of a modified force-free current sheet, with periodic boundary conditions in
all directions. In all cases, the linear and non-linear evolution led to a
primary current sheet between two large flux ropes. The global reconnection
rate during this later stage was analyzed in all simulations. It was found that
in 2.5D the primary current sheet fragmented due to plasmoids, and as expected,
the global reconnection rate, calculated using multiple methods, increases with
the strength of the reconnecting field due to a stronger Alfv\'{e}n speed. In
3D, the presence of interacting oblique modes of the tearing instability
complicates the simple 2.5D picture, entangling the magnetic field of the
inflow and introducing a negative effect on the reconnection rate. The two
competing effects of stronger Alfv\'{e}n speed and entangling, which both
increase with the strength of the reconnecting field, resulted in a decrease in
the reconnection rate with increasing reconnecting field. For all simulations,
the 3D rates were less than in 2.5D, but suggest that as one goes to weak
reconnecting field (or strong guide field), the system becomes more 2.5D like
and the 2.5D and 3D rates converge. These results have relevance to situations
like nano-flare heating and flare current sheets in the corona.
