When members of TrueDelta’s panel sell an enrolled car and buy a new one, they email me so I can make the change. In recent months, I’ve noted many cases where a large, powerful vehicle was traded for a smaller, more efficient one. And very few cases of the opposite.

It seems that size and power are on the way out, in the face of rising gas prices and a probable economic downturn.

This week leading industry trade journal Automotive News also noted this trend with a front page story, “Downsizing arrives – with a vengeance.” Apparently, Ford executives are calling the current shift in consumer preferences “seismic.”

In other words, it’s not expected to be momentary. The age of the 268-horsepower Toyota Camry may be at an end. Sales of four-cylinder cars are surging, while Chrysler’s HEMI is just so 2006.

The hottest car in TrueDelta’s panel right now? The tiny, three-cylinder Smart ForTwo. The car only recently became available in the United States, yet already nearly 50 are enrolled in the panel. We’ll even have an initial result for the car in May.

The opposite can be seen in the number of Chrysler 300s, Dodge Chargers, and Dodge Magnums enrolled: 75 2005s, 140 2006s (when the Charger and SRT8s arrived), 28 2007s, and only 6 2008s.

Expected to get hurt the most: Detroit auto makers, who over the course of the 1990s and the first few years of this decade relied more and more on large trucks for sales and profits.

I performed some research for my Ph.D. inside GM back in 1996 and 1997. Back then, and probably still today, GM spoke of having a “product portfolio.” I suggested that they manage this portfolio the same as they would a stock portfolio, and diversify. By having a broad range of products and the ability to flexibly shift production among them, they wouldn’t always be one step behind the market. Instead, wherever the market shifted to, they’d already be there.

But this isn’t what they did. And so, once again, they–along with Ford and Chrysler–are a step or two behind.