To ensure that the signal goes from the shifter to the derailleurs the reliability of the electric cable has been proven by repeated field tests in various riding conditions including extreme temperatures rain mud & cobble stone roads The removal of traditional mechanical cables in favour of electrical wires not only eliminates poor shifting caused by contaminates corrosion & stretching but provides effortless gear shifts Dura-Ace Di 2 requires 2 cables: a handlebar cable set to connect the shifters to a battery indicator junction box or Flight Deck & the other to connect the handlebar cable to the battery & derailleurs. This battery to derailleur cable is available for internal or external routing in different lengths allowing for various frame sizes External cable sets are ideal for upgrading your current bike to Dura-Ace Di 2 if it does not feature the internal cable routing option Internal cable sets are for bikes specifically designed for Di 2 to ensure clean lines & minimal rider interference External cables are available in varying lengths there is no need &40;or facility&41; to cut these cables Reliable & secure water resistant connectors