On the inventory side, growth is being driven especially by crossovers, Smoke said.
"If you're a consumer shopping for a crossover you've got more supply than you've ever had on both the new and used lot," he said.
At the same time, it has become increasingly difficult to find lease deals on cars such as Honda Accords or Toyota Camrys. That is boosting prices for older, used versions of those vehicles, which are also in dwindling supply, he said.
The shift in used-car and truck sales has been accelerating since the first quarter of 2015, when the two categories were nearly even, with cars holding a slight edge, according to J.D. Power figures. In that year's first quarter, both categories grew, with cars up 5 percent and trucks up 10.7 percent. Used-truck sales have subsequently grown in each first quarter, rising 6.5 percent in 2017, 9.6 percent in 2018 and 4.1 percent in 2019. That compares with declines for cars of 6.4 percent in the comparable period of 2017, 1 percent in 2018 and 8.8 percent in 2019.
Auction volume of compact SUVs soared 30 percent year-over-year to 183,756 vehicles in the first quarter, passing midsize cars, which had been the dominant segment in 2018, according to J.D. Power. Midsize cars dropped 11 percent, but still came in at a hefty 176,830 vehicles, Banks noted. Wholesale volume of midsize cars is expected to continue to decline, while that of midsize SUVs will rise, he said. That should set up some interesting dynamics for prices in these segments.