The structure of styrene鈥揵utadiene (SB) nanocomposites filled with industrial silica has been analyzed using electron microscopy and small-angle X-ray scattering. The grafting density per unit silica surface 蟻D3 was varied by adding graftable SB molecules. By comparing the filler structures at fixed 蟻D3 (so-called 鈥渢wins鈥?, a surprising match of the microstructures was evidenced. Mechanical measurements show that 蟻D3 also sets the modulus: it is then possible to tune the terminal relaxation time of nanocomposites via the chain length while leaving the modulus and structure unchanged.