NEW YORK (CNNMoney.com) - Not too long ago, if you wanted a real high-performance vehicle -- one that started fast, accelerated quickly and cornered hard -- you bought a sports car.

These days, you can buy a family sedan, a station wagon or even an SUV that would blow the doors off a sports car made only a few years ago. The performance of these vehicles, which is often astounding given their size and weight, owes a lot to small engineering improvements made, in many cases, for other reasons.

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Many of these improvements were referred to in a recent article on the increasing fuel efficiency of vehicles over the past 20 years, while fuel mileage actually stayed the same. That is because technological gains in fuel efficiency, instead of being used for better mileage -- something that American car buyers seem to actually care little about -- were used for increased size and speed.

The average vehicle weight has gone up by about 900 pounds over that time, from 3,200 pounds to almost 4,100 pounds. Despite that, vehicles are also faster today. Overall, the average zero-to-sixty time for all passenger vehicles in America in 1981, as calculated by the EPA, was 14.1 seconds. Today, the average is 9.9 seconds.

At the extreme end of these trends are SUVs, station wagons and big four-door cars that perform in ways that would have been unthinkable 20 years ago or, in some cases, even 10 years ago.

Unibody construction, in which a vehicle's roof, door frames and floor pan are part of a unified, rigid structure, has made vehicles lighter and stiffer. That, in turn, means that vehicles are less subject to twisting forces in hard turns. It also means that vehicles can use stiffer suspension systems without all the bolts and doors shaking loose.

More powerful engines mean that even heavier vehicles can accelerate quickly. Sports cars could accelerate quickly with a little over 100 horsepower because they were extremely light. The big V-8 engines in some high-performance SUVs now have over four times that much power, enough to take a 4,000-pound vehicle to 60 miles an hour in under six seconds.

"We're starting with vehicles that are far superior to what we had 20 years ago," said Cole Quinnell, a spokesman for DaimlerChrysler's Chrysler Group engineers.

Computer modeling allows today's auto engineers to precisely design vehicles, engines and transmissions, down to the smallest detail, for maximum strength without having to repeatedly build and test actual components over and over along the way, said Quinnell.

More sophisticated suspension systems mean that big vehicles can maintain a firm sense of control in hard turns without needing to have a punishing ride. Still, for a high performance SUV like the Jeep Grand Cherokee SRT-8, the suspension does have to be stiffer than drivers of ordinary SUVs would probably like.

Many more-expensive vehicles today have adjustable suspensions which can be set by the driver by just pressing a button, for cushy cruising or aggressive driving. Others have suspension systems that automatically sense how hard the driver is cornering and automatically adjust shock absorbers' stiffness to give the best handling.

Land Rover's Range Rover Sport uses anti-sway bars that are engaged only when sensors detect that the vehicle is going through a fast turn. In slower driving, the anti-sway bars aren't engaged, allowing for better off-road performance.

Improved automatic transmissions have also had a big effect in allowing for performance in larger packages. Few buyers of large vehicles want a stick-shift transmission. But a stick shift offers the advantage of being able to change how you shift gears depending on the situation. If you're after performance, you can stay in lower gears longer for maximum acceleration and you can downshift, using drag from the engine to help slow the car.

Many automatic transmissions today have a "sport" setting that holds off on upshifts as long as possible and that keeps the gears engaged even when the driver takes his foot off the accelerator.

While the degree of control still isn't as precise as a manual transmission, just changing the shift points can make a vehicle feel like it's suddenly grown a much bigger engine. Allowing for the quick change means that a big car can get reasonably good fuel mileage in ordinary driving but rev high when more performance is wanted.

Run-flat tires have also added performance capabilities. Because of their size and weight, it would be prohibitive to have a spare for the performance wheels and tires on many of these vehicles.

Tires themselves are also better at maintaining the kind of grip needed to keep heavy vehicles on the road during hard cornering.

"Today we have materials like Kevlar and carbon fiber in tires that can handle the speed capabilities of these vehicles," said Matt Edmonds, vice-president of TireRack.com, a tire retailing Website.

Technology like electronic traction control and electronic stability control also add a degree of safety when putting high-powered vehicles like these on the street. Although manufacturers and experts are careful to point out that these systems can't undo every fool-hearty driving maneuver, they can, at least, prevent a slight misjudgement from becoming an automatic disaster.

There is still a place in this world for good old-fashioned sports cars, of course. Performance for those types of vehicles has improved over the years, as well, so a modern sports car will still perform far better than any SUV. That's why Porsche still makes the 911 sports car in addition to the Cayenne. But try picking up some plywood sheeting in that 911.

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