What The Hell Is Going On With Tesla Model S Wheels On Impact?

There’s no doubt that the Tesla Model S is a safe car; it obtained a five-star safety rating from the National Highway Traffic Safety Administration and Euro NCAP.
However, following crash tests conducted by The Insurance Institute for Highway Safety (IIHS), it rated the car’s small overlap front crash test (conducted at 40mph) as ‘acceptable’ (out of good, acceptable, marginal and poor). IIHS had this to say:

The Model S, a large luxury sedan, earns good ratings in all IIHS crashworthiness evaluations except the challenging small overlap front crash test, in which it earns an acceptable rating. Despite lengthening the side curtain airbags to improve small overlap protection in the Model S, 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.

By contrast, the Chevy Volt, Toyota Prius Prime and BMW i3 all scored ‘good’ ratings in this area. What’s more, the headlight crash test (yes, that’s a thing) scored the Tesla the lowest ‘poor’ rating, with the i3, Prius and Volt scoring ‘Acceptable’, ‘Acceptable’ and ‘Good’ respectively.

Of greater concern, however, is the behaviour of the car’s aluminium alloy wheel. On small frontal impact, the wheel cracks and dramatically shatters, further reducing crash structure integrity and launching projectiles into the surrounding area. (The wheel does not crack in the greater, load bearing moderate frontal impact test).
We reached out to Tesla and were given this statement (not directly related to the problem wheel, but hopefully something it will look into with immediate effect):

“We are committed to making the world’s safest cars, and Model S has previously received a 5-star safety rating from the National Highway Traffic Safety Administration and a 5-star rating from Euro NCAP. Model S still has the lowest ever probability of injury of any car ever tested by NHTSA.

We proactively develop updates and aggressively implement changes onto the production line in record time any time there is a substantial benefit to customer safety. One of the improvements recently introduced in January 2017 specifically addresses the “Acceptable” (or second highest) rating that the Model S achieved in the small overlap frontal crash test, and we expect new tests to yield the highest possible rating (“Good” rating) in the crashworthiness category.

Additionally, IIHS tested a vehicle that was in transition with new Autopilot hardware, but without the new software that enables Automatic Emergency Braking. In the coming weeks, Automatic Emergency Braking will be deployed via a free over-the-air software update, and IIHS will be testing a new vehicle. We expect to receive the highest possible rating in every category, making Model S eligible for the IIHS Top Safety Pick award.”

The combustible wheel doesn’t only concern me in extreme crash tests like this, because I now question what could happen at 100mph on the Autobahn if a pothole were to be struck or a stray object (like a rock or a piece of car) were to be run over…