The removal of traditional mechanical cables in favour of electrical wires not only eliminates poor shifting caused by contaminates corrosion and stretching but provides effortless gear shifts the sm ew90 b 5 port di2 junction a from shimano is required to connect the shifters via e tube wires to the down tube junction wire this one features a battery level indicator and an additional charging point when using an internal battery and a gear index setup switch to allow fine tuning via shifter