TIRUPUR, India — When Alan Greenspan ran a consulting firm and wanted to know where the economy was headed, he would often look at sales of men’s underwear as a guide.

Mr. Greenspan, who later served as chairman of the Federal Reserve, believed that when times were tough, men would stop replacing worn-out underwear, which no one could see, before cutting other purchases.

By that measure, India is in a serious slump.

“Sales are down 50 percent,” said Jeffrin Moses, gesturing toward the boxes of cotton briefs and tank tops bulging from the shelves of the Tantex undergarment emporium in Tirupur , the southern city where most of the country’s knitwear is made.

It’s not just underwear. Car sales plunged 32 percent in August, the largest drop in two decades, and carmakers are w arning of one million layoffs as shoppers balk at rising prices and struggle to get loans from skittish lenders. Macrotech, a big real estate developer that has teamed up with President Trump on a residential tower in Mumbai, just laid off 400 employees as demand for new housing sinks.