Different behaviours have been observed by shearing the smectic phase of side-chain polymers. They present under shear flow, either a parallel layer orientation, a perpendicular layer orientation or a multilamellae cylindrical geometry. These different behaviours are analysed on the basis of a comparative description of the conformational architectures at equilibrium. They differ either by the molecular weight or by the flexibility of the main-chain of the mesomorphic polymer. It will demonstrated that the main-chain characteristics allow to explain the different orientations adopted under shear flow.