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Electric vehicles weigh a lot; are the safety issues surrounding possible rollovers keeping automakers from building more open-air EV models?
We now have electric sedans, SUVs, pickup trucks, supercars, and even hypercars. But what about convertibles? The pickings are slim, and one reason for that may be safety. Standard practice is to put heavy battery packs underneath the floor, which increases interior space and beneficially lowers the vehicle’s center of gravity.
But in a rollover situation, that heavy battery pack could easily crush the fragile soft top—and the occupants inside. The good news is that the same down-low pack acts to prevent a rollover in the first place.
Volkswagen is considering a convertible version of the ID.3 electric hatchback, but plans may not have gone much beyond the renderings (as seen at the top) shown last year from SRK Designs. Other concepts have come from Bentley (the EXP 12 Speed 6E, circa 2017) and Nissan (a Leaf convertible, circa 2018), though there are no production plans. Mini seems intent on offering an electric convertible by 2025.
Plug-in hybrid (PHEV) fans can order their Jeep Wrangler 4xe (the bestselling PHEV in America) with a power retractable soft top, but that’s essentially a large folding sunroof—not a full convertible. The forthcoming Jeep Recon EV, which will start production in 2024, is also open-air, with “a one-touch powertop, removable doors and glass,” Jeep said. The BMW i8 PHEV was briefly offered in convertible form, but is discontinued.
EV convertibles we’ve lost include the Smart Fortwo Electric Drive Cabrio and the original Tesla Roadster. A new edition of the latter is reportedly coming, but despite the name it’s not really a “roadster” in the classic sense. It has a removable glass roof that can be stored in the trunk, a targa-type configuration. The heavy Hummer EV also has removable panels.
Those recent designs, and that of the Jeep, might suggest that automakers are consciously keeping some type of hard roof over the heads of people in EV convertibles. The VW ID.3 concept and the Mini design are outliers as full ragtops, but the VW at least is more of an idea than a car.
The law isn’t going to stop full-convertible EVs. Michael Brooks, acting executive director of the Center for Auto Safety, points out that the National Highway Traffic Safety Administration (NHTSA) regulation governing roof crush resistance, #216a, specifically exempts convertibles (and school buses, if you can believe it). “It’s a challenge to build a temporary roof structure that will satisfy the standards,” Brooks said.
General Motors spokeswoman Natalee Runyan said via email, “The GMC Hummer EV pickup and the upcoming Hummer EV SUV both have removable roof panels for open-air driving, and we’ve committed to a future with electrified Corvettes.” It isn’t yet confirmed that the hybrid and/or battery electric Corvette, which could be called the E-Ray, will be available as a convertible, but GM Authority said, “We expect the Corvette C8 E-Ray to be available as a two-door coupe (with a removable hardtop panel) and a hardtop convertible.” The current Corvette is available in the latter format.
“All else equal, a lower center of gravity can certainly help keep a vehicle upright.”
—Joe Young, IIHS
Some EVs, including that Hummer EV pickup, are real heavyweights. The latter tips the scales at 9046 pounds, with a 2923-pound battery. “There are a lot of safety considerations involving weight,” said Brooks, who added that he thinks convertible EVs are “doable” with smart design thinking.
“A rollover would certainly pose a risk to someone riding in a convertible of any kind,” said Joe Young, director of media relations at the Insurance Institute for Highway Safety (IIHS). “Convertibles are exempt from NHTSA’s roof-resistance standards, but many include safety features like stronger A-pillars or roll bars to mitigate risk in a rollover. I can’t say how those features might hold up in a heavier battery-powered vehicle.”
IIHS crunched data on conventional convertibles and found that they aren’t statistically any more dangerous than vehicles with fixed roofs—though ejection was more common.
And the same battery pack that could be dangerous in an EV convertible rollover could also make it less likely to roll over in the first place. That’s according to Jake Fisher, senior director of auto testing at Consumer Reports. “Because they have so much weight low down, the propensity to roll over is very low,” Fisher said. “Having a low center of gravity puts these vehicles in a much better position.”
IIHS’ Young agrees: “All else equal, a lower center of gravity can certainly help keep a vehicle upright.” EVs overall seem to be doing fairly well in terms of safety.
Consumers who buy SUVs might be reassured by “having all that metal around them,” Fisher said, but SUVs also tend to have higher centers of gravity—which increases rollover risk.
Any discussion of EV convertibles has to reflect their fate in the larger market. Last year, convertibles were less than half a percent of sales in the US. Americans still love the Mazda Miata (especially on race tracks) but the company only sold 10,547 in the US for 2021. How many people would buy an electric Miata, which is said to be coming? If automakers are avoiding EV convertibles, it may just be that they don’t think consumers will buy them.
Share your thoughts on the feasibility of designing and building—and selling—convertible EVs in the comments below.