The rubber will definitely not insulate you. In fact, the rubber in car tires is not enough to insulate you. The reason you are safe in a car has nothing to do with the tires. Air is also an insulator and almost as good as rubber. The bolt just travelled through 2 miles of air, so a few inches of rubber doesn't mean anything. It's also been said that you are in a Faraday cage (for metal cars, not so true for convertables or fiberglass/plastic cars). But the Faraday cage only works with static electricity, when a bolt of lightning hits, it is moving quite rapidly. So the real reason you are safe in your car is something known as the "skin effect". Lightning behaves like a short burst of of very high frequency alternating current. The skin effect has to do with the magnetic field of the AC pushing the current to outside of a conductor. Thus the current flows on the outside of the car and into the ground. Since the current would be flowing on the outside of your bike, and you are on the outside, you are not protected by this effect.