You'd need a supercomputer to process all the variables that affect your premium. To name a few, these include your driving record, claims history, credit history, age, gender, type of car insurance you purchase, where you live and the type of car you drive. While the whole picture is greater than the sum of its parts, the type of vehicle you buy has a substantial impact on the car insurance premium you pay, especially if you purchase comprehensive and collision coverage.

According to the National Association of Insurance Commissioners, comprehensive and collision coverage accounted for 47.6 percent of the combined average premium paid nationwide in 2005 (the most recent data available). The combined average premium includes liability, comprehensive and collision coverage.

Comprehensive and collision insurance premiums are calculated by looking at a vehicle's loss history — that is, how often that model is stolen and how much it costs to repair or replace it after an accident.

Generally speaking, your car model does not affect the premium you pay for liability insurance alone, but there are exceptions. Sports cars, high-performance cars and intermediate-performance cars may cost more in liability premiums.

To help price the risk of your car, many insurance companies use vehicle ratings designated by the Insurance Services Office (ISO), a statistical and actuarial reporting group for the insurance industry. The ISO publishes a manual used by insurers and agents that rates each vehicle based on its loss history, meaning how much is typically paid out in claims for that car. (The exception is the very first year of a model, when a percentage of MSRP is used to set premiums.)

Jeff De Turris, assistant vice president at ISO, says that each vehicle is assigned a number between 1 and 27 to represent the cost of comprehensive and collision coverage. A vehicle with a higher rating will have a higher premium.

"Insurers may, at their own discretion, use them without modification, modify them or not use them," Turris says. "Many factors other than the symbol also affect the premium."

ISO won't disclose exactly how it determines its ratings, except that they are based on loss history. According to ISO's Web site, it's unlikely that a $30,000 minivan would generate the same amount of theft losses as a $30,000 sports car, or that the damage sustained in an accident for a $40,000 luxury car with a fiberglass-based body would be the same as damage to a $40,000 sports utility vehicle. Turris adds that even styles within the same model can carry different ratings. That means that the EX, LX or touring-edition vehicle of the same model won't necessarily have the same rating.

State Farm's own Vehicle Saftey Ratings are accessible to the public on its Web site. Among other information, it shows if you will be charged a "standard premium," "significantly higher-than-standard" or "significantly lower-than-standard" premium by State Farm. For example, Honda's Odyssey and Pilot both fall into State Farm's "significantly less-than-standard premium" category while a Lamborghini Gallardo or a Lotus both cruise into a "significantly higher-than-standard premium" category. A Ford Taurus falls into a standard premium category.

Sports cars take you higher

If you drive a certain sports car, you could pay hundreds of dollars more annually for insurance. For example, according to an online insurance quote from GEICO, a single 40-year-old male who works as a hospital administrator in a Chicago suburb, and who hasn't had an accident or ticket in the past 5 years, will pay $547.80 a year to insure a Honda Odyssey. (This buys him $300,000 of bodily injury coverage, $100,000 for liability damage, and comprehensive and collision coverage.) He would pay $1,438.80 for the same coverage for a Porsche 911. That's $891 more per year.

If you're planning to purchase a new car, your insurance agent can tell you how much your premium will go up or down, or you can find out by requesting insurance quotes online.

"Having that information may affect the purchase decision and avoid unpleasant surprises after the purchase," Turris says.