Wrong, wrong, wrong. Wrong.

You're relatively safe in a care because you are surrounded by metal. The rubber has NOTHING to do with it. The electricity travels through the metal and not through you; it takes the path of least resistance, the steel in the car.

When you're out in a lightning storm, you have hundreds of meters of air between you and the source of lightning, the clouds, and air is an insulator too. THAT doesn't stop the lightning, what makes you think an inch of rubber is going to stop it?

Also, rubber in tires is NOT really an insulator; most tire rubber contains carbon black for durability, and that is actually conductive.

If lightning strikes, it's going to evaporate that puny rubber tire. Heck, it'll explode car tires. We had a lightning strike near our house and a tiny part of it bled into our dog's invisible fence wire buried in the ground, and after most of that energy blew half the insulation off the 1300 feet of wire, a small part of it made it to the transmitter, blew half the components off the circuit board inside, travelled into the power transformer and exploded the windings like there was a ball of C4 inside it. Power like that doesn't give a damn about an inch of rubber.

Personally, riding in a lightning storm doesn't worry me all that much. The odds of any given thing getting hit is pretty low. If I were riding in Florida where lightning strikes many more times per minute, I might be more worried. In Michigan you can stand outside in a lighting storm for an hour and probably never see a strike within a quarter mile of you.