We have investigated the efficiency of scattering processes through acoustic phonons in semiconducting nanotubes. Based on the density matrix formalism we obtain Boltzmann scattering equations, which give us a microscopic access to the time- and momentum-resolved relaxation dynamics of optically excited carriers. In agreement with a recent experiment [see Dyatlova et al., Nano Lett. 12, 2249 (2012)], we obtain relaxation times on the picosecond time scale. Here we study the importance of carrier–phonon interaction as a function of probe energy and initial temperature for the exemplary (8,7) nanotube. Furthermore, we calculate the relaxation dynamics for nanotubes with different diameters focusing on the change in the relaxation time with the curvature of the corresponding energetically lowest conduction subband.