John Archibald Purves looked at the automobile and decided it contained too many wheels. Around 1930, the British engineer demonstrated the Dynasphere, a motorized monowheel in which the vehicle, engine, driver, and passengers all occupied the inside of one enormous rolling shell. Purves reportedly called it the high-speed vehicle of the future. The future declined.

The mechanism was stranger than simply enlarging a tire. Engineer Margaret Partridge described an outer hollow sphere with its opposite sides cut away, a loose tramway-like track inside that shell, and a heavy powered carriage running on the inner track. As the carriage tried to move along the inside, its weight and motor drove the outer ring across the ground. Versions could seat two or more people inside the lattice.

Purves demonstrated the machine at the Brooklands motor-racing course and on the beach at Weston-super-Mare. The rotating lattice looked like it should make forward vision impossible, but Partridge argued that the bars crossed the eye so quickly they blurred away, leaving the country ahead visible between them. She praised the machine's mobility and economy and noted that its controls resembled those of an ordinary car. Period photographs treated the giant wheel as a plausible new era rather than a parade prop.

One wheel also concentrated several problems. Balancing, steering, accelerating, and braking all happened through the relationship between the inner carriage and the outer shell. Popular Science later described the risk of "gerbiling": a sudden change could send the passenger carriage spinning inside the wheel instead of remaining politely at the bottom. The comparison has outlived the machine because it explains the failure instantly.

The Dynasphere never became a commercial success. It survives instead as a beautifully literal invention: put a car inside its own wheel and let the engine climb the interior until the world rolls underneath. Purves removed three wheels and discovered that each of them had apparently been doing something important.