Two door vehicle do not always cause your insurance to rise since individual insurance companies have their own rating systems, however many 2 door cars are deemed to be sports cars and thus may cost a little more to insure.
A sports vehicle will be rated higher by most insurance companies than a family sedan. This is due to sports vehicles parts normally cost more to repair plus they are statistically in more accidents at higher speeds, thus appear to insurance underwriters as more of a risk.
The classification of a car as a sports car, family car, etc will depend upon the definitions set forth by an insurance company. Each insurance company has its own vehicle classification system that is typically based upon ISO (Insurance Services Office) VIN system or other company proprietary ranking systems.
You click here for a free car insurance estimate and can put in both 2 door and 4 door vehicles to see if there is a cost difference for insuring these vehicles with the insurance companies we are partnered with.