How the Tesla Model S Narrowly Missed A Poor Crash Test Rating

The Tesla Model S narrowly escaped being given the lowest score possible on an important Insurance Institute for Highway Safety (IIHS) crash test. The story started when the Tesla Model S was first crash tested by IIHS this past winter. The Model S scored only “Acceptable” on the small frontal overlap test. This was a surprise for Tesla, who had for many years bragged that the Model S was the safest car in America. A test that everyday cars like the Honda Civic and Chevy Bolt earned a score of “Good” on with no problems had just tripped up the $100K Model S.

Background On The Small Frontal Overlap Crash Test

The small frontal overlap test was designed by IIHS and other parties to simulate a vehicle traveling at 40 MPH crashing into a utility pole or an oncoming vehicle, but only with 25% of the front of the car making contact. This test puts a lot of force on a small part of the front structure and is the most difficult to ace crash test American market vehicles are subjected to. The old-school NHTSA tests do not match the difficulty of the IIHS tests and are conducted at lower speeds. Speed matters a lot in crash tests since kinetic energy is increased by the square of the velocity.

When first tested, IIHS reported the problems that the Model S had, saying, “Tesla ran into problems in the test when the safety belt allowed the dummy's torso to move too far forward. That allowed the dummy's head to hit the steering wheel hard through the airbag. Measurements from the dummy indicated that injuries to the head, along with the lower right leg, would be possible in a real-world crash of the same severity.”

Tesla Model S Struggles To Earn A Good Score On Crash Test

As the Institute sometimes does, it granted Tesla a second chance at the test because Tesla had claimed to have addressed this problem with a production revision. A re-test is no small undertaking. A new vehicle would need to be destroyed. Even the least expensive Model S costs over $75,000. The second test had the same overall result but uncovered a bigger concern than an “Acceptable” rating might indicate.

Background – Vehicle Fire Possibilities In Crash Testing

Some background is required on crash testing and how IIHS scores vehicles that may catch fire. In a liquid-fueled vehicle test, IIHS drains out the gasoline from the vehicle and replaces it with Stoddard Solvent, a fluid that is less volatile than gasoline. The fluid is weighed before and after the test to determine if any leaked out, and the fluid is dyed purple so there can be a visible inspection for leaks. When testing EVs, IIHS is similarly careful to take note of any damage to the battery pack or the high-voltage power systems. Damage to a battery pack can lead to a fire (and has) so IIHS takes added precautions to avoid a fire in the facility. Just one of the special measure IIHS takes is to reduce the charge of the EV’s battery pack prior to the test. IIHS’ spokesperson Russ Rader explains the scoring of test vehicles, saying, “If there’s a fuel leak in a conventional vehicle, or damage to the high-voltage system in an electric car, the rating is an automatic Poor.”

Tesla Model S Battery Case Damaged In Crash Test

The Model S crashed in the second IIHS small frontal overlap test still had injuries to the dummy that resulted in an “Acceptable” rating. However, the two tests didn’t have similar results with regard to the left front wheel’s movement back into the passengers' space and vehicle platform. IIHS says in its report, “Maximum intrusion increased from less than 2 inches (in test 1) to 11 inches (in test 2) in the lower part and to 5 inches at the instrument panel in the second test.“ IIHS goes on to mention an important detail, adding, “The greater deformation in the second test also resulted in damage to the left front corner of the battery case.” (Don't Miss Tesla's Response On Page 2)

The battery case in an electric vehicle surrounds and protects the high voltage system of the vehicle. So why didn’t IIHS immediately score this test “Poor?” The reason is that not all Model S cars are the same. The trim tested by IIHS was the least expensive trim, called the 60. The 60 had the least number of battery cells in its battery compartment of the available trims for sale during testing. Other models, like the 75, 90, and 100 have more batteries and the added batteries occupy that space in the battery case in those models. IIHS says that the reason it didn’t follow its normal default protocol to score this test a “Poor” result is, “The deformation was limited to an area that didn't contain battery cells in the tested vehicle, so this damage didn't affect the rating. Higher-performance variants of the Model S could have battery cells in this area, but, according to Tesla, they also have different structure. They haven't been tested separately and aren't covered by this rating.”

It appears that Tesla was cut some slack and that IIHS took Tesla’s word for it that the added structure in other trims would withstand the damage of the crash. The resulting score of "Acceptable" didn't come from the damaged battery case at all, but as David Zuby of IIHS explains in the video below, were because Tesla's claimed correction didn't stop the dummy's head from missing the airbags and hitting the steering wheel hard.

Following the release of the report of the IIHS testing of large cars, which included the Model S, Tesla issued the following statement to CNBC: "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."