The interaction between longitudinal acoustic waves and Bragg gratings is numerically investigated for suspended core fibers. The incicle core is increased from 1 to 6.6 µm and the mechanical properties and the grating properties are calculated using a finite element method and a transfer matrix method. Interestingly, while the generated strain in the core increases with decreasing core diameter, the achievable side lobe reflectivity of the Bragg gratings is reduced.