"Longer loan terms, coupled with the current low interest rate environment, increases the affordability of new vehicles for consumers," said Thomas King, senior director of consulting and analytics at J.D. Power.
(Read more: Americans rethinking how they buy cars)
As the auto industry has rebounded over the last five years, consumers have been looking for a way to pay for more expensive vehicles, while keeping their monthly payment as low as possible.
Another factor behind the trend is the rising popularity of leases. J.D. Power said 26.5 percent of retail sales this month are leases, a new record high. The previous record was 26 percent, set in May 2000.
(Read more: Tesla soars, Ford down: 'Consumer Reports')
"Unlike buyers who finance their vehicle and have considerable discretion regarding when to return to market, consumers who lease their vehicle must come back into the market when their lease terminates," King said.
"The current level of leasing means there will be a steady and significant stream of lessees returning to market three years from now."
—By CNBC's Phil LeBeau. Follow him on Twitter
Questions? Comments? BehindTheWheel@cnbc.com.