A lower residual value means either lease customers have to finance a bigger amount or auto lenders have to spend that much more on incentives to keep monthly payments low.
But purchase customers could also be affected because lower residual values imply lower resale values, Lyman said in an interview last week.
"People do tend to think of residuals being only important to lease customers," he said. But "unless you plan to keep a car until it's rusted out 20 years down the road, you're going to turn it over at some time in the near future." The residual value therefore "should be a consideration in your purchase decision," he said.
Gas prices, of course, aren't the only factor driving residual values. Consider supply.
Large used pickups and SUVs are relatively scarce right now compared with historical volumes due to weak sales of new vehicles two and three years ago. Small-car volumes are correspondingly bigger, and the supply of small, fuel-efficient cars is expected to grow even more in coming years as automakers shift production to more of those vehicles. Indeed, some analysts predict a glut of small cars will torpedo their residual values.
For instance, ALG said that in the September/October issue of its Residual Value Guide, it will cut its 36-month predicted residual value for the Ford F-150 by $376. That's the net effect of an $849 cut connected to anticipated higher gas prices, offset in part by a $473 boost based on the scarcity factor, the company said.
Conversely, the Honda Fit will get a $503 boost for fuel efficiency, but that's more than erased by a negative $1,552 for an expected abundant supply, resulting in a $1,049 cut in its residual value, ALG said.
Using buyer behavior for the past 10 years, ALG recently took a new look at how vehicle purchases changed when gas prices went up and when they went back down, Lyman said.
The latest analysis showed that for every $1 that gasoline prices increase, residual values for full-sized pickups and SUVs should drop about 10 percent. At the same time, residuals for compact cars should rise about 10 percent. That's isolating gas prices as a single factor, without taking relative scarcity or abundance of different vehicle segments into account.
ALG predicts that three years from now, gasoline will cost around $4 a gallon, Lyman said. On average that's not much higher than today's prices, and many areas are already paying $4 or more. According to the AAA Fuel Gauge Report, the national average for regular unleaded was about $3.68 on Tuesday, July 19. That's 96 cents higher than a year ago, but down from a recent peak of about $3.95 in May.
Lyman said the effect on residuals could be greater if gasoline prices rise more quickly or if they pass some psychological barrier, such as $5 a gallon or, say, $100 per fill-up. He added: "We are not taking into account any expected psychological impact."