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AUTOMOTIVE CHASSIS DESIGN has a relatively concise history: Body-on-frame follows practices dating back to horse-drawn carriages. Unibody is a 20th-century innovation. And skateboarding is likely to be the 21st-century norm.
Richard Truett’s “The EV Skateboard: The Innovation That’s Redefining the Auto Industry,” Automotive News, September 5, 2022, is replete with tidbits about this transition. I supplement with my usual Internet sleuthing (including some SimanaitisSays items.)
Body-on-Frame. Coachwork perching atop a structure containing the mechanical bits is the traditional idea, and it’s still with us today in full-size pickups, large SUVs, and commercial vehicles. A stout chassis is amenable to off-road and other rugged use. What’s more, it enables easy styling changes: Only the body gets revamped; the mechanical bits below can carry over. (Remember this restyling idea when we come to skateboards.)
These days, one body-on-frame disadvantage is its less than optimal energy-absorbing crumple zones for crash safety. Another can be weighty construction.
Unibody. Truett observes, “The first high-volume unibody vehicle was the 1934 Citroen Traction Avant. Among other early unibody cars was the Chrysler Airflow, also introduced in 1934.”
Unibodies are ubiquitous today in cars, crossovers, minivans, and even a few pickups. Truett cites weight savings and hence fuel economy as advantages of this integration of chassis and bodywork. Rigidity and energy-absorbing controlled crush are beneficial in crashworthiness.
There are unibody disadvantages as well: Styling changes are difficult and complex. Accident and rust repair are more costly than body-on-frame’s.
The Next Step: Start with a Talented Team. Chris Borroni-Bird was director of GM’s Advanced Technology Vehicles Concept group. Larry Burns was GM R&D chief. Together with MIT’s William J. Mitchell, they wrote Reinventing the Automobile: Personal Mobility for the 21st Century in 2010.
Truett writes, “It was Borroni-Bird’s team, empowered by former GM R&D chief Larry Burns, that created the AUTOnomy skateboard concept, which debuted at the 2002 North American International Auto Show in Detroit.
“That first skateboard,” Truett notes, “was not designed for BEVs, however. GM’s vision for the first application was for a hydrogen fuel cell and drive-by-wire technology, all of which was packaged in the 6-inch-thick skateboard chassis. Later, a skateboard would underpin GM’s fully driveable Hy-Wire hydrogen concept car.”
Skateboard Benefits. Borroni-Bird tells Truett, “”When you think about a ground-up design for an electric vehicle, the skateboard is the obvious choice, the obvious solution. You lower the center of gravity, improve road-holding, have more freedom in design, you get better crash protection for the front of the vehicle, and there’s more storage, so it creates a lot of benefits.”
The skateboard is not without disadvantages: It lacks the heavy-duty benefits of rugged body-on-frame. Its integration of mechanicals is not particularly amenable to repair or maintenance.
Nevertheless, Truett reports, “The skateboard chassis just might be the most important piece of automotive hardware created this century. Not only has it been key to making EVs viable, it has also opened a door for dozens of startups looking to seize the opportunity.”
Skateboard surf is up. ds
© Dennis Simanaitis, SimanaitisSays.com, 2022