Tesla defends the Model S and its safety record.

In a statement to CNBC, a Tesla rep said: “Tesla’s Model S received the highest rating in IIHS’s crash testing in every category except for one, the small overlap front crash test, where it received the second highest rating available. While IIHS and dozens of other private industry groups around the world have methods and motivations that suit their own subjective purposes, the most objective and accurate independent testing of vehicle safety is currently done by the U.S. government, which found Model S and Model X to be the two cars with the lowest probability of injury of any cars that it has ever tested, making them the safest cars in history.”

It’s true the National Highway Traffic Safety Administration has given both the Model S and the Model X five-star safety ratings, the highest score possible. In fact, the Model X is the only SUV to ever earn a five-star rating from the federal government.

So, why the difference between the two crash tests? NHTSA’s evaluation does not include small overlap front-end collisions, which the IIHS blames for about a quarter of the injuries and fatalities in front-end crashes.

“We would argue, that to be considered the safest vehicle on the road, it should earn a ‘Good’ rating from the IIHS as well as a five-star safety rating from NHTSA,” Zuby said.

Of the six large cars to be tested by IIHS, three received the designation of being “Top Safety Picks.” Those models include the Lincoln Continental, Mercedes-Benz E-Class and Toyota Avalon.

Questions? Comments? BehindTheWheel@cnbc.com.