While rubber is an electrical insulator, the tires are not thick enough to effectively insulate the vehicle from a lightning strike.
Rubber does play a minor role in protecting passengers by forming a partial barrier that can help distribute the electrical current and minimize direct contact with conductive metal parts, however that protection alone is far from sufficient protection in case of lightning impact.
For actual protection when in a car the main safeguarding effect comes from the metal frame of the vehicle acting as a protective Faraday cage that surrounds and protects the passengers
