Nothing wrong or rare about the suspension on the Tammy Sherman. The HVSS (Horizontal Volute Spring suspension) is a much better suspension which wasn't available until mid 1944. It greatly decreased ground pressure as well as providing as smoother ride over ground that would have stopped the earlier Shermans, but added more than a ton to the tank's weight. The problem with the Tamiya Sherman is that is was an infantry support tank, as opposed to the standard combat Shermans. It was issued much more sparsley to tank units, starting with one to a company. For that reason it is not that popular, so many have been converted to other Shermans. My only Tammy is a Sherman but I converted it to an Israeli M-51 and it runs great.