Nissan says its 2.5L 4-cyl. ’13 Altima midsize sedan should earn a segment-best 38 mpg (6.2 L/100 km) highway when it goes on sale this summer in the U.S.

The fifth-generation Altima debuts today at the New York International Auto Show, while the ’12 coupe carries over for ’13.

The 38-mpg highway rating for the new Nissan 4-door exceeds the ’13 Ford Fusion’s expected 37 mpg (6.4 L/100 km) for models powered by a 1.6L EcoBoost gasoline engine. The current midsize best-seller, the Toyota Camry, achieves 35 mpg (6.7 L/100 km) highway from its non-hybrid 2.5L 4-cyl. models.

The 2.5L-equipped ’13 Altima is expected to earn 27 mpg (8.7 L/100 km) city and 31 mpg (7.6 L/100 km) combined, Nissan says.

The carryover QR25 engine, now making 182 hp compared with 175 hp in the ’12 2.5L Altima, adds variable valve timing on intake and exhaust camshafts and a thermoplastic resin intake manifold for reduced weight and improved efficiency.

Torque still peaks at 180 lb.-ft. (244 Nm), but for a flatter curve Nissan’s new intake system opens valves at a higher rpm, the auto maker says.

Class-leading fuel economy and an overall premium feel were two development directives for the new Altima.

“The targets were to have this car appear to be something higher up than a midsize sedan, for both interior and exterior,” Scott Shirley, a director and chief marketing manager for Nissan, says at a recent Detroit media preview at Nissan’s Farmington Hills, MI, tech center.

The ’13 Altima, on sale in the U.S. in July, has flowing lines reminiscent of Nissan’s luxury Infiniti-brand models, as well as the Nissan Ellure concept car from the 2010 Los Angeles auto show.

A longer sloping rear roofline and taller trunk “combine to create a more fluid silhouette,” Nissan says. The car also sports a new front fascia with a concave grille design. A prominent character line starts above the front wheels, dipping below the front door handles, rising again above the rear door handles and then straightening out.

The new midsize sedan retains the current Altima’s wheelbase but has 1.4 ins. (3.6 cm) wider front and rear tracks and 0.8 in. (2.0 cm) deeper fenders.

A glimpse of the 3.5 SL grade’s interior at the Farmington Hills center reveals a circular knit headliner fabric that also covers the visors, soft-touch materials on the upper instrument panel and door panels, and matte metallic and carbon-fiber-like trim.

Nissan says it used zero-gravity research from the National Aeronautics and Space Administration to create fatigue-reducing seats in the Altima, noting continuous support from the pelvis to the chest lessens muscular and spinal loads and improves blood flow.

To quell cabin noise, Nissan increases overall body rigidity and uses new engine- and exhaust-mount designs, as well as 30% more noise-absorption materials in the new Altima compared with the outgoing 4-door.

High-strength and ultra-high-strength steels take 80 lbs. (36 kg) out of the sedan’s body, which Nissan touts as already one of the lightest in the class at 3,180 lbs. (1,442 kg).

Because 10% of Altima sales are V-6 models, the auto maker will continue to offer the engine option, unlike the upcoming Fusion and Hyundai’s Sonata. The current 3.5L 270-hp “VQ” engine, a 14-time Ward’s 10 Best Engines winner, carries over to the ’13 model.

Most of the fuel economy gains for both the 4-cyl. and V-6 powertrains are due to a 70%-redesigned continuously variable transmission, Nissan says. The new CVT has 40% less internal friction than the previous unit and expanded gear-ratio coverage, which not only cuts fuel use but also lessens noise and improves drivability and responsiveness.

The 3.5L mated to a CVT is estimated to achieve 22/30 mpg (10.7-7.8 L/100 km) city/highway, or 25 mpg (9.4 L/100 km) combined, Nissan says. A manual-transmission will not be offered for the new Altima sedan.

A new hybrid model also is due, the auto maker promises.

Nissan says it benchmarked luxury sport sedans such as the BMW 3-Series and its own Infiniti G in crafting the ’13 Altima’s new multilink rear suspension. New connect bushings improve toe angle control, and improved camber angle control increases the amount of tire contact with the road in cornering maneuvers.

ZF Sachs shock absorbers balance body control and provide a smooth, flat ride, Nissan says.

The auto maker touts a few segment-first technologies on the ’13 model, including a predictive Active Understeer Control system. Designed for everyday use, it employs the Altima’s standard traction and stability control systems to brake inside front wheels as necessary in cornering, via intelligent control logic and brake actuators.

A 4-view rearward camera, now with a wider field of vision, is available, as are blind-spot and lane-departure warning systems and moving-object detection.

A 4.0-in. (10-cm) color display is standard on all ’13 Altima sedans. Fuel economy, audio settings, tire-pressure readouts and navigation information are viewable.

The ’13 Altima sedan will be the first Nissan with the auto maker’s new NissanConnect telematics system. NissanConnect includes Bluetooth, Pandora, USB port and SiriusXM Satellite Radio. It also has a text-messaging assistant that reads incoming messages from paired smartphones and offers preset answers such as “driving,” “can’t text” or “running late.”

The ’13 Altima begins at $21,500 for a 2.5 grade model with CVT and tops out at $30,080 for the 3.5 SL grade. S and SV grades are slotted in between base and SL models.

A $590 navigation package is available for SV grades, while a technology package that includes navigation is $1,090 for SL models. Destination and handling is $780 for the ’13 Altima.

Serial production begins May 15 at Nissan’s Smyrna, TN, plant, followed three weeks later at the Canton, MS, facility, which is the primary source of the car.

In addition to the U.S., the ’13 Altima will be sold in the Middle East, Russia and China. Nissan exports about 15%-20% of the current-generation Altimas built in the U.S. to 45 countries, Shirley says.

The auto maker sold 268,981Altimas last year, making it the second best-selling midsize sedan in the U.S., WardsAuto data shows. Nissan says about 20% of current-generation Altimas are sold to fleets, with most going to corporate fleets rather than daily rental.

cschweinsberg@wardsauto.com