We investigate coupled excitonic and vibrational effects in carbon nanotubes using a time-dependent Hartree-Fock approach. The results reveal intricate details of excited-state dynamics. In the ground state, spontaneous uneven distribution of the pi electrons over the bonds (i.e., Peierls dimerization) is observed throughout the entire nanotube, particularly in large-radius CNTs. However, we demonstrate that vibrational relaxation following photoexcitations leads to substantial local distortion of the tube surface, overriding the Peierls dimerization. This mutually affects the electronic system, resulting in localized states (self-trapped excitons). These phenomena critically control photoinduced dynamics and charge transport in nanotube materials.