To remedy the problems aforementioned, bifunctional organosilanes also known as coupling agents, for example bis(3triethoxy silylpropyl)-tetrasulfide (TESPT), are added to modify silica. The addition of an increasing loading of TESPT improved dispersion of silica particles in rubber.19 Silica and TESPT interact in two ways. Firstly, silica and TESPT are mixed together in the required ratio and homogenized in an additional preliminary mixing stage.20 Alternatively, silanization is carried out in situ. This is usually done in an internal mixer at the first stage of mixing, where TESPT is added together with or after the addition and dispersion of the silica.21