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The 1960s: Prototyping the ATC

If necessity was the mother of the first ATV, Honda engineer Osamu Takeuchi was its father. In 1967, American Honda asked Honda R&D Ltd. for a new product dealers could sell when motorcycle sales cooled off in the winter. Mr. Takeuchi was assigned to lead the project, along with a small group of engineers. This was clearly the group for the job, since Takeuchi and company had been working to develop other new recreational vehicles that never saw production. These projects gave Takeuchi the tools to develop Honda's first ATV, the US 90.
Forget the proverbial blank sheet of paper. Takeuchi started in the shop with a head full of ideas and an eclectic assortment of components. Two, three, four, five and even six-wheeled configurations were examined, but the three-wheel concept delivered the best combination for the machine's intended mission. It dealt with snow, mud and assorted slippery conditions a two-wheeler couldn't, while providing more maneuverability than other configurations.

In the early stages, a Honda ST70 motorcycle gave up its 70cc four-stroke single-cylinder engine for the cause, along with assorted chassis parts. An extended rear axle carried cultivator wheels designed to handle rough terrain. Two driving wheels in the rear worked well. Cultivator tires didn't. The biggest challenge would be finding a tire capable of getting a grip on soft, changeable terrain such as snow, sand and mud. Two wheels, three wheels, four wheels or more? Motorcycle tires weren't an option.
The design process quickened when Takeuchi received an American invention called the "Amphi-Cat¨ that rolled on six 20-inch low-pressure, high-flotation balloon tires. The light bulb went on. Revamping his ST70-based prototype to accept the new low-pressure rolling stock, he went to work on his own tire design, ending up with a 22-inch design inflated to 2.2 psi. With the tire dilemma solved, the 70cc engine lacked the muscle necessary to push a full-sized rider through snow or mud. A 90cc engine running through a special dual-range four-speed gearbox added the requisite flexibility over varied terrain.
The next phase of development was optimizing the chassis to match the new engine and tires. Testing over rough roads, sand hills and slopes as steep as 35-degrees gradually established chassis dimensions effective for recreational riding as well as agricultural work. Laid out in the shape of an isosceles triangle with the footpegs located outside the triangle to optimize control, the ATC design was unique enough to let Takeuchi patent the arrangement.
Exhaustive testing brought other lessons to light as well. Using a thumb throttle instead of the typical motorcycle twist grip let riders shift their weight for optimal vehicle maneuverability while maintaining precise throttle control. A rear differential was considered, but discarded when a live axle performed better. Though suspension is an integral part of the modern ATV, Takeuchi's original balloon tires soaked up rough terrain best by themselves. Exerting less pressure on soft or sensitive terrain than the average human foot, those tires let the vehicle go places others couldn't, leaving little or no evidence of their passing--an advantage that looms large in hundreds of modern ATV applications.