Are declining sales the beginning of the end of modern muscle? TIGHTENING POCKETS COULD BE THE DEATH OF MODERN MUSCLE MACHINES

After hitting a five-year peak in 2015, combined sales of the Ford Mustang, Chevrolet Camaro and Dodge Challenger have declined 8.4 percent this year.

So is it time to worry about America's fabled muscle-car troika?

Possibly not, because the decline this year nearly matches the 8.5 percent drop in overall car sales as crossovers and SUVs keep rolling up gains. Yet the cool-down of America's muscle-car mania could have deeper meaning.

Customers who buy Mustangs, Camaros and Challengers do so because they want modern evocations of 1960s performance icons, not because they need them, says Karl Brauer, senior director of insights for Kelley Blue Book. And that could be a problem.

"You have the canaries in the coal mine -- cars that are more discretionary rather than functional purchases, and cars that you see starting to decline first" when the market starts to plateau or dip, he says. "We're seeing that in two areas -- luxury brands are struggling more, and so are these performance cars."

Indeed, luxury car sales have fallen 13 percent year to date in a total market that's up 1.1 percent.

In 2015, muscle-car sales shot up 22.6 percent for the first seven months. In 2014 and 2015, the three cars handily outperformed the overall car market.

But sales of all three cars have dropped this year: Mustang down 5.5 percent to 72,530; Camaro down 15.4 percent to 42,354 and Challenger down 5.5 percent to 39,998.

Chevrolet spokesman Jim Cain attributes the Camaro's steeper drop to the fact that last year, Chevrolet was headed into a model change-over.