In the automotive world, there is a perverse version of "trickle-down economics" taking place. Makers of new vehicles are suffering, and those who deal in used vehicles are feeling the pain as well.

Shares of CarMax Inc. fell 4% Wednesday after the operator of used-car dealerships said comparable same-store sales fell 17% for the months of June and July, falling off dramatically after Memorial Day weekend, when the price of gasoline spiked to about $4 a gallon.

Outside gasoline, one reason used-car dealers such as CarMax are getting hit is because of the massive inventory clearance undertaken by the major automobile companies, who have again increased incentives and lowered prices.

The newest problem that has cropped up for the big auto makers is in the leasing market. Ford Motor Co. and General Motors Corp. took large write-downs based on the reduced residual values of cars that had been leased but are not being purchased by consumers.

Many of these are SUVs, and the prices of used SUVs have declined by about 28% on a year-over-year basis, much more than anticipated.

In a sense, used cars have become an ersatz collateralized-debt-obligation market, where the value of the underlying asset is believed to be at one level until the discovery later shows the value is actually much less. The timing couldn't be worse for the auto industry.

"The problems with [declining] residual values are not new either to the domestic or import markets, but everything is magnified now," says Rebecca Lindland , director of automotive-industry research at Global Insight.

Why does this hurt the likes of CarMax? They are put in the position of having to reduce prices on their own cars, hurting margins. Furthermore, CarMax operates primarily in late-model used cars, a more volatile market than used cars in general, according to Zacks Investment Research analyst Paul Raman , who adds that competition in this area increases advertising costs.

Shares of the stock closed at $14.87 Wednesday, compared with a 52-week high of $25.55 reached Aug. 8, 2007 and a 52-week low of $10.53 reached July 15 of this year.

Oddly enough, the decline in the leasing market may eventually benefit CarMax.

With car companies curtailing their use of leases, late-model used cars could become "a more attractive option for some consumers," writes Scot Ciccarelli , analyst at RBC Capital Markets. "Nevertheless, we think it is too early to get involved in the stock given the lack of visibility."