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, and cobble stone roadsThe 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 shiftsDura-Ace 7970 Di2 requires 2 cables: a handlebar cable set to connect the shifters to a battery indicator junction box or FlightDeck, and the other to connect the handlebar cable to the battery and derailleurs. This battery to derailleur cable is available for internal or external routing in different lengths allowing for various frame sizesExternal cable sets are ideal for upgrading your current bike to Dura-Ace 7970 Di2 if it does not feature the internal cable routing optionInternal cable sets are for bikes specifically designed for Di2 to ensure clean lines and minimal rider interferenceExternal cables are available in varying lengths, there is no need (or facility) to cut these cablesReliable and secure water resistant connectors