Tesla Upgrades Battery Protection With Aluminum and Titanium Shielding

In November HybridCars.com interviewed safety experts about Tesla’s underside armor who suggested strengthening would be advisable following two U.S. fires, and today CEO Elon Musk said Tesla has done just that.

And, the federal government dropped its investigation of battery fires, a seemingly independent decision but with murkiness as to what was said between Tesla and government regulators.

Effective Mar. 6, Model S electric sedans rolling off the Fremont, Calif. assembly line were equipped with a triple shield made of aluminum and titanium designed to prevent underbody damage that could puncture the battery and precipitate a fire.

Although the car was the subject of a federal investigation, Tesla reported no news from that.

In follow-up with the National Highway Transportation Safety Administration, the agency said this upgrade has satisfied its investigation.

It did not answer specific and repeated questions as to whether the Tesla upgrades were resultant from discussions with NHTSA, either by suggestion, direct federal order, or otherwise. NHTSA only issued a brief boilerplate statement which did not answer whether the armor was purely Tesla’s decision, or not.

Safety is our top priority. The National Highway Traffic Safety Administration has decided to close our investigation of the Model S Vehicle. NHTSA believes the company’s revision to the vehicle’s ride height and increased underbody protection should reduce both the frequency of underbody strikes and the risk of resulting fires. Consumers should have their vehicles serviced promptly once they receive notification from Tesla Motors.

Musk said the new shield has deflected all sorts of hardened objects in 152 tests simulating a car running over something at random on the road, such as a three-ball trailer hitch.


Tesla even positioned a spear in the road and let the electric sedan hit that and no fire resulted. Other items included an automotve alternator and concrete block, both of which were crushed and deflected.

The trailer hitch was a concern as such an item caused a fire last fall in Washington by a “piking” event – essentially a high-force lever action that sent the hardened steel through the underbody.

Tesla’s new system prevented that from happening.

Triple Shield

The first of three shields is a rounded hollow bar made of aluminum. This is intended to either completely deflect objects of with something like a three-ball trailer hitch which is “self stabilizing,” absorb and force it to pike far in front of the battery pack.

Instead the plastic aeroshield and frunk liner may be pierced but this hasn’t been shown to disable the car or affect occupant safety.

Another shield is a high strength-to-weight titanium plate protecting sensitive front underbody components.


These two by themselves are enough to have deflected most objects, Musk said, but a third shield was added.

“For the rare piece of debris that remains intact, we added a third shield, which is a shallow angle, solid aluminum extrusion that further absorbs impact energy, provides another layer of deflection and finally causes the Model S to ramp up and over the object if it is essentially incompressible and immovable.

The new shields do slightly affect range, but their effect is minimal, said Musk.

“In total, the shields only have a 0.1 percent impact on range and don’t affect ride or handling. Wind tunnel testing shows no discernible change in drag or lift on the car,” he said.

Optional Upgrade

Musk said the Model S was already super safe, despite overblown headline coverage suggesting the opposite.

“The odds of fire in a Model S, at roughly 1 in 8,000 vehicles, are five times lower than those of an average gasoline car and, when a fire does occur, the actual combustion potential is comparatively small,” said Musk of the original Model S aluminum cladding under the battery pack.

The company also did an on-air software adjustment that increased the default ground clearance, and now this updated triple shield is icing on the cake, essentially.


“Nonetheless, we felt it was important to bring this risk down to virtually zero to give Model S owners complete peace of mind,” he said.

Musk also gave dramatic evidence of the previous car’s safety citing the high-speed crashed that ripped the wheels of a Model S in Mexico, and said the new shields will prevent a fire in such a scenario.

“This happened after the vehicle impacted a roundabout at 110 mph, shearing off 15 feet of concrete curbwall and tearing off the left front wheel, then smashing through an eight foot tall buttressed concrete wall on the other side of the road and tearing off the right front wheel, before crashing into a tree,” said Musk. “The driver stepped out and walked away with no permanent injuries and a fire, again limited to the front section of the vehicle, started several minutes later.”

In follow-up with NHTSA asking whether it ordered Tesla or not to make the upgrades, an answer not addressing the questions was returned.

Is the underside of the Model S the only thing being shielded, or is Tesla’s reputation also? This question remains after further followup with NHTSA and evasive answers dodging pointed questions as to its degree of involvement in Tesla’s decision.

From HybridCars.com:

Questions were the ones I asked originally. I would rather talk with you, but in advance of that, did NHTSA collaborate on the design or testing of the shield? Was the shielding at the recommendation or direct order of NHTSA? I need the background story on these apparently two separate events. – Thanks!


On background and attributable to NHTSA:
After further discussion between NHTSA and Tesla, the automaker stated it would conduct a free-of-charge service campaign to modify the SVs by adding three new components to the vehicle’s undercarriage to protect the HVB. A low-hanging transverse member and an additional underbody plate would be mounted forward of the HVB case and a third plate would overlap the leading edge of the case. While NHTSA’s investigation has formally closed, the agency will continue to monitor all available data and take future action if warranted.

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