Spherical Tires: Might Autonomous Cars Be Borne on Airless Basketballs?

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All tires are round, right? Yes, but only when viewed from the side. From straight ahead or above they’re kind of rectangular, which is why they only roll in two directions. How limiting! Wouldn’t omnidirectional, spherical tires be awesome? They’d allow slide-in parallel parking with millimeters to spare, zero-yaw lane changes, and pivot-in-place U-turns.

I paid scant attention when Audi teased the idea with its RSQ product placement in the 2004 Will Smith future film, I, Robot. After all, it’s called science fiction for a reason. But Goodyear has now brought successive generations of its Eagle 360 tires to two successive Geneva Motor Shows. Are spherical tires about to become a thing?

Here’s Goodyear’s vision: Because there’s no place to put a Schrader valve and no easy way to access it, the tires are airless. Some type of foam—the company is cagey about its composition—would permit the deflection required to achieve a useful contact patch. At the center is a smaller rigid graphene sphere that houses an array of powerful permanent magnets. These magnets are used to levitate the bodywork above the tires. They’re also used to provide acceleration, braking, and turning in response to powerful electromagnetic windings in the wheel housings surrounding these spheres. Frictionless drive—another plus!

Goodyear Eagle 360 Urban Spherical Tire

Goodyear freely admits to having expended little or no effort toward sorting out the vehicle integration aspects of making its wheel/tire concept propel a car such as the RSQ except to say that such a car would be autonomously driven (thus eliminating the control challenges of steering four omnidirectional tires). San Jose State University made a motorcycle run (to 10 mph) on spherical tires back in 2012, but that concept punted on the mag-lev and touchless electric drive in favor of a series of motor-driven rollers that provided friction drive directly to the tires.

Can Goodyear’s vision work? Being a mere mechanical engineer, I reached out to Tim Grewe, GM’s general director of electrification to find out. Surprisingly, he foresaw no technological roadblocks. Yes, you could mag-lev a car body. And yes, you could simultaneously accelerate and steer wheels that were also providing magnetic levitation—even with windings that can’t completely surround the rotor. But it would take a lot of power. You could even brake a vehicle this way, though generating sufficient electric braking force would require resistors or big ultracapacitors capable of disposing the surplus energy that the battery couldn’t absorb.

I also batted the idea around with our favorite engineering techspert COTY judge, Chris Theodore. We concluded that full damping and body motion control would probably be best provided by mechanical means over and above the mag-lev, which would then only be required to maintain its consistent (small) gap to the tires. We also reckoned parking would require stanchions that deploy to support the vehicle when the mag-lev energy was cut.

What neither Chris nor Tim could envision was a scenario under which this ultra-complicated concept would prove more efficient or effective than supporting and driving a vehicle by more mechanical means. Some sort of casterlike omnidirectional steering of conventional wheels and tires with hub motors could achieve most of the same maneuverability goals far more simply.

Rather than holding my breath for spherical tires, I’m therefore keeping an eye out for the other technologies demonstrated by the Eagle 360 tires: internal sensing of the tread-wear status and road surface grip levels with the ability to communicate this information to the driver and other road users via V2X technology, self-healing 3-D-printed tread compounds that behave like a natural sponge—stiff when dry, softer when wet—a bionic skin made of a super-elastic polymer that can modify its tread pattern to suit driving conditions with the help of actuators beneath the surface, and possibly even airless foam-supported construction. But for now, I’m considering those Genevois basketball tires a long way from a slam dunk.

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