We have statistically studied magnetotail variations associated with expansion onsets for storm and nonstorm time substorms, using Geotail data. Here storm time was defined as Sym-H ≤ -30 nT. It was found that there are no qualitative differences in magnetotail variations between these two types of substorms, although the energy accumulation and the dipolarization tend to be more significant during storm time substorms. The statistical results evidently show that the magnetic reconnection and the dipolarization do occur in the magnetotail around onset for both types of substorms, suggesting that storm and nonstorm time substorms are caused by the same mechanism.