The increasing SUV and truck popularity, and discount-fueled sales of some midsize cars, helped U.S. auto industry to its best August in 11 years last month, with sales rising 5.4 percent from a year ago.

DETROIT — The seismic shift in American car-buying toward trucks and crossover SUVs is creating great deals on compact and midsize cars.

The shift, which has been going on for more than a year, is hurting car sales so much that automakers are offering bigger discounts to keep moving metal.

The change became even more pronounced in August, with companies such as General Motors and Chrysler reporting that truck sales, including crossover SUVS, were up while car sales fell.

The increasing SUV and truck popularity, and discount-fueled sales of some midsize cars, helped U.S. auto industry to its best August in 11 years last month, with sales rising 5.4 percent from a year ago to 1.58 million, according to Ward’s Automotive. While prices remain high for trucks and SUVs, they’re either falling or rising only slightly on cars, and that’s good news for consumers.

“It’s definitely a good time to buy a midsize car,” says Jessica Caldwell, senior analyst at the Edmunds.com automotive website. Every midsize sedan is comfortable, looks good and performs well, so price is nearly the only differentiator, she says.

Automakers spent an average of $1,841 per car to discount compacts last month, up 7 percent from a year ago, while prices fell 1.2 percent, according to estimates from Edmunds. On midsize cars, companies spent an average of $2,344 on discounts, up 4 percent. Average sales price rose slightly as buyers added features.

Of major automakers, only General Motors and Volkswagen reported sales declines last month. GM was down 1.2 percent; VW was off nearly 13 percent.