A recently developed method to calculate gas-phase mobilities by scattering on electron density isosurfaces (SEDI) has been applied to carbon cluster ions. The investigation has covered species belonging to all major structural families identified in drift tube studies (chains, monocyclic and bicyclic rings, graphite sheets, and fullerenes). Relative cross sections of C-n(-) and C-n(+) predicted by SEDI are in excellent agreement with the measurements across a wide range of cluster sizes and shapes. However, absolute values could not be fit for either charge state. This happens because SEDI ignores the long-range ion-buffer gas interaction known to be important for many systems including carbon clusters. To overcome this problem, we propose a new technique to evaluate mobilities by coupling SEDI with trajectory calculations. This approach allows one to introduce the repulsive interaction accurately and still account for the attractive part of the potential. This hybrid SEDI-TC treatment has been found substantially superior to all models previously described in reproducing both absolute and relative mobilities of C-n anions and cations.