Pocock first described the Sumatran tiger on the basis of several skull, pelage, and striping features, which are distinct from the Bengal and Javan tigers. It is darker in fur colour and has broader stripes than the Javan tiger. Stripes tend to dissolve into spots near their ends, and on the back, flanks and hind legs are lines of small, dark spots between the regular stripes. The frequency of stripes is higher than in other subspecies.
Males have a prominent ruff, which is especially marked in the Sumatran tiger.
This site contains all information about Sumatran Tiger Vs Siberian Tiger.