Some of the components of tires are conductive but the rubber itself is not so much - put an ohm meter to them to see for yourself. Or, you can find video's of tests done that show the arcing in slow motion.
The lightning jumps for many miles so jumping from the cars body or metal wheel to earth is nothing. Car tires being conductive or not would have absolutely no effect. The car could be suspended in mid air and still have no effect on lightning flow.
Keep in mind that I'm not saying tires are insulators, I'm saying it doesn't matter because tests show lightning jumps over them.