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 ultegra di2 uses a fully removable individual cable system from the battery indicator junction box enabling fine tuning with the correct cable length to each component for easy and tidy fitment ew sd50 wires are required to connect the junction either sm jc40 external or sm jc41 internal to the rear