The subcompact car segment suddenly finds itself with several new models just as it once again becomes quite relevant. As gasoline prices bump up against the $4-gallon threshold, will buyers embrace these new competitors for a longer period of time? Will these innovative small cars really become profitable for their makers? Will these products become more than just a fad, the latest flavor of the month in the auto industry?

Well, the early signs are positive as this crop of rivals — a blossoming class that includes the Ford Fiesta, the all-new Chevy Sonic, the Mazda 2, Honda’s established Fit, an all-new Toyota Yaris, plus the Korean twins, the Kia Rio featured here plus Hyundai’s Accent — is starting to generate much higher sales figures as well as greater consumer interest. Nissan’s Versa is sometimes considered part of this class, however it lacks a hatchback model and it is much longer than most of these cars. Suzuki’s SX4 could be considered a contestant here as well. Chrysler has no offerings in this segment.

That the cars themselves are much more credible, with more safety features, better levels of refinement and equipment, plus, finally, interesting styling, proves that the automakers are serious about making inroads in the high-mpg, small car segment.

Interestingly, most of the new subcompacts presented in the U.S. market share similar styling attributes that mirror the winning designs from Europe, where these cars have dominated sales for decades. While there are some sedan variants in this group, most of the aforementioned rivals are selling well as five-door hatchbacks — a layout that affords greater versatility and functionality, attributes inherently more beneficial in a package that is much smaller than many drivers are accustomed to.

Small cars have historically made great sales gains when the price of gasoline rises, but once consumers become accustomed to the higher prices or grow weary of the small car experience, sales level off or die altogether. That may not occur this time as A) the B-class subcompact cars are generally much better than anything we have previously experienced, and B), higher fuel prices are exacting a far greater economic toll than ever before.

Year to date, the sales numbers help define that story. Incredibly, Chevy’s new Sonic has rocketed up the sales charts to lead the category with over 13,000 units sold in the first two months of 2012. Hyundai’s Accent is number two, the Fiesta is in the number three slot, while Honda’s Fit — the former segment leader and supposed benchmark vehicle — has slid all the way to fourth place. The Kia Rio and the Toyota Yaris are neck and neck for fifth place, with everyone else in the rear-view mirror. Total segment sales have doubled over last year.

Critics have lauded the Honda Fit for several years, but the sales numbers partially illustrate why that car has been eclipsed by the new entries in this class. This week’s Kia, as well as the Accent and Chevy’s Sonic, all offer direct-injection 138-horsepower 1.6-liter engines (the Chevy also offers a turbocharged 1.4-liter engine with the same power and more torque). This is 18-32 more horsepower than the rest of the class with no apparent mileage penalty as the Kia, the Hyundai and the Chevy all earn the valuable 40-mpg EPA highway mileage number that is perfect for advertising bragging. The weakly powered Yaris, Fit, Suzuki and Mazda do not. (The Fiesta earns the big 40-mpg number in special versions.)

In the real world, that 40-mpg number is the new bellwether of your efficiency — automakers club each other when they earn it and tout it repeatedly. Achieving this number, however, is quite elusive.

The EPA test for highway miles per gallon includes a relatively flat land area in a temperate climate with a maximum speed of 60 mph. There are no long grades, no freezing temperatures, no heavy winds and no cruising at 75-80 mph like most of America travels on the freeway. E-10 gasoline — the bane of truly efficient driving — is used.

After my test Rio arrived on an 86-degree March day, the weather took a much more seasonal turn. Snow returned, the wind blew — a lot — and the mercury hovered closer to freezing than it did the delightful temps of our early spring. Mileage was affected.

This was clearly evident on a long highway run north to Presque Isle into a strong headwind. With the Rio’s on-board trip computer indicating 36 mpg (two to three miles a gallon optimistic) at the entrance to I-95, the cold, gusting northwest wind quickly exacted its toll as the car’s speed matched the new higher limit on the long road north. The combination of the heavy wind, the long grades headed north and the elevated speed of the highway, often caused the Rio’s six-speed automatic transmission to drop out of overdrive sixth gear for long periods. By the time we exited the highway at Houlton, the Rio’s trip computer indicated only 27.4 mpg — a number that quickly became only 25.4 mpg once the 11-gallon tank was refilled. EPA mileage estimates for the Rio are 30-mpg city, 40-mpg highway.

On the return trip southbound, the temperature had increased 10 degrees to 31 and the wall of wind was now at my back. The Rio was much more relaxed — with the transmission rarely downshifting out of sixth gear — and, traveling at the same exact pace, returned an actual 33.2 mpg.

While many of today’s new car buyers eschew the standard manual transmissions on small cars, the Kia’s performance indicates that the six-speed manual may be the hot ticket for maximum power and fuel efficiency. Acceleration testing by third parties confirms this impression.

Over the course of 730 miles together the Kia revealed several other impressions.

Inside, the Rio pummels its rivals with a lengthy list of equipment and features. There is a price-leader LX model that starts at only $13,400 — tying the Fiesta for lowest price in the segment (add $200 for the five-door hatchback edition) while the fully loaded SX version tested, $17,700, makes you forget why you previously had such an aversion to small cars.

With an upscale audio system including Sirius, Bluetooth access, steering wheel controls and multiple auxiliary jacks the Kia distances itself from Honda and Toyota. Add automatic headlamps, fog lights, heated mirrors with turn signal lamps, full trip computer, one-touch lane change action, cruise control, one-hand folding rear seats, plus a 10-year/100,000-mile warranty and the Kia moves ahead of the Fiesta, Mazda and Nissan.

The Rio’s small hatch reveals a deep cargo bin and a surprising amount of space. Flip the seatbacks forward and there is an amazing amount of cargo room compared to a conventional subcompact sedan. Rear seat space is also surprisingly adult-friendly with ample foot and headroom for 6-foot-tall passengers. Two adults will easily fit in the back, with two more 6-footers upfront, so no passenger compromises are necessary.

While one would wish for more range from the tilt/telescoping steering column, and a power seat might offer a greater range of comfort, the Rio’s real shortcoming is the chassis’ compromised ride dynamics. On smooth roads, the suspension is a model citizen; steering feel is a bit numb (like most cars today) while the handling is perfectly acceptable. Throw out some rough surfaces and an undulating path and the chassis reacts with a plodding that belies unrefined damping and soft springs that are apparently confused. This is not just a Rio trait, but a malady that afflicts almost every Korean car. While the majority of drivers might never be offended — or even notice this trait — those buyers who consider themselves something more than steering wheel operators will reflect on the Kia’s comparatively unsophisticated suspension performance.

Chassis engineering is definitely a soft-science that eludes many automakers — either by cost choice or philosophy. Just ask the automakers that continue to chase BMW.

If Kia, and Hyundai, connect the dots in this area — like they have with their expressive exterior styling and feature-laden interiors — then these cars will be top-notch competitors in every perspective and pricing will be irrelevant.

The newest Rio looks a lot like the Fiesta, the new Sonic and the Accent. That tells us this is the Euro-template that everyone has arrived at for success in the American-marketplace. Budding sales confirm that the subcompact segment has legs and the new entries mean business. Watch Rio sales continue to climb in the coming months.

The Kia Rio comes in three flavors, LX, EX and SX. All are powered by a direct-injection 1.6-liter four-cylinder with 138 hp and 123 pound/feet of peak torque. Buyers can select either a six-speed manual or six-speed automatic transmission in sedan or five-door hatchback body with EPA mileage estimates of 30/40-mpg. EX models are available with an optional stop-start feature and push button ignition.

Rio five-door measures 171.9 inches long on a 101.2-inch wheelbase. Base weight is 2,400 pounds. By comparison, the Rio is 1 inch shorter than both the Ford Fiesta and Chevy Sonic but 10 inches longer than the Honda Fit and 18 inches longer than the Toyota Yaris hatchback. The Rio’s wheelbase is the longest amongst this group.

SX trim includes 17-inch alloy wheels, hill assist control, electronic stability control, UVO entertainment system, manually adjustable driver’s seat, steering wheel cruise and audio controls, rear cargo cover, LED lamps and Sirius satellite radio.

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