Despite Harley-Davidson’s all-American reputation, the Thai plant will not be its first abroad — or even in Asia. The company opened a similar plant in Bawal, India, in 2011 to help it get around that country’s 100 percent tariff on imported motorcycles. It also assembles motorcycles at a plant in Brazil and has a wheel factory in Australia. The Thailand plant will assemble motorcycles for Asia that were previously imported from India or the United States.

Harley-Davidson’s made-in-Thailand motorcycles will avoid the country’s up to 60 percent tariff on imported motorcycles. They would also get a huge break on tariffs when exported to Thailand’s neighbors, thanks to a trade deal among the 10 members of the Association of Southeast Asian Nations, or Asean.

The Thai plant is also intended to help serve a vast market in mainland China. Asean is pursuing an enlarged free-trade area with Beijing. And Mr. McAllister of Harley-Davidson said the Thai plant would lower the transport and shipping time to the Chinese market to around five to seven days, from 45 to 60 days from the United States.

For big companies, “the economics are increasingly compelling, and Asean is again attracting the lion’s share of foreign direct investment into Asia, after China had been the primary destination for many years,” said Frederic Neumann, a co-head of Asian economic research at HSBC in Hong Kong.

By contrast, many of those nations charge steep tariffs on foreign-made goods like Harley motorcycles.