The ignition systems in modern cars can reach up to 100,000V and can only arc up to about 6 to 8 feet, lightning travels miles and actual voltage depends on distance. Amperage determins size of the conductor and voltage determins the insulator. In another words you could be completely in-cased in 5 feet of rubber and a lightning strike would still go through it. Graphite is semi-conductive and is used in ignition wires to increase voltage (it is induced voltage from the coil with voltage increasing with resistance) and reduce EMI. With a fly rod it isn't just the material of the rod but the length, electricity always looks for the easiest path to ground. Also, electricity flows on the outside of a conductor, not through it. The metal body of a car is the reason why being in a car during a lightning storm is the safest place, not the tires.