The average length of a car loan was 48 months a few years ago, according to the auto industry consulting firm AutoPacific.
These days, it's 66 months.
"There are quite a few 96-month loans out there, which is kinda scary to think," says the group's Ed Kim.
"If you're doing a 96-month loan, you're going to be upside down on that car for a very, very long time."
Honda Financial recently said it would not offer the longer term loans, because they depress future car sales.
But other lenders are still offering them.
"People aren't going to be able to replace their cars as quickly as they have in the past, because they're going to be upside down on those loans for a significantly longer time," says Kim.
The longer loans are one reason Kim is forecasting a decline in car sales beginning in 2018.
Another big reason is the length of time that younger millennials are staying out of the car market.
He says it's more difficult for younger drivers to get a license, because so many states have adopted graduated licensing requirements.
And he says many millennials are substituting socializing with friends via social media, rather than face-to-face, so they have less incentive to own a car.
AutoPacific forecasts car sales will reach 17 million in the U.S. this year, and increase to 17.2 million in 2016.
If that happens, it will be a record. The cyclical U.S. car industry has never had seven straight years of car sales increases.
Kim says the departure from the trend reflects how bad car sales were during the Great Recession.
"There was really no where for the industry to go but up."
