By Jim Meachen and Ted Biederman

The Infiniti Q50 (formally known as the G37) is a good example of how to improve an already first-class mid-sized luxury sedan enhancing the car's driving behavior, modernizing exterior and interior styling, and adding cutting-edge technology and safety features taken to the next level.

The Q50, in its second year of production, advances the brand with an outstanding V-6 powertrain that actually produces the same horsepower and torque ratings as the last G37 in 2013 — 328 horsepower, 269 pound-feet of torque routed through a seven-speed automatic — but feels more responsive thanks to the outstanding transmission that stands ready to explore the vast reaches of the rev band.

The bottom line is that Infiniti made an excellent decision to retain this very capable 3.7 that defies its published performance numbers. The numbers are solid — 0-to-60 in just a tick or two above five seconds and a quarter mile 13.5 seconds at 102 — but the car actually feels stronger in real-world driving conditions, perhaps because of its flexible power delivery.

Some automotive reviews to the contrary, our test car handled one of our favorite stretches of winding road in exemplary fashion. Where does the recurring "disappointing handling when pushed" mantra come from? We discovered that we were driving a different car than those criticized by reviewers who found issues with the sedan's high-speed handling and cornering, and therein lies the strange aspect of the Q50 and our asterisk.

Let us explain. The biggest difference comes where the rubber meets the road, in other words — tires. All trim levels as well as the hybrid variant of the Q50 come with all-season Bridgestone run-flat tires. Reviewers have complained about lack of grip and audible protests from those tires when pushed hard. To get first-class handling traits — something owners of the G37 have come to expect — opt for the $1,800 Performance Wheel Package on the Q50S (Sport) trim level that brings 19-inch summer performance tires. The Q50, which sits on a two-inch wider body and sports a new rear suspension — together with a sport-tuned version in the Q50S model — produces smile-inducing road-carving traits with the non-run-flat summer tires.

Another bone of contention is Infiniti's pioneering drive-by-wire steering system technology, called Direct Adaptive Steering (DAS). Some reviewers like it while others say the computer-controlled steering feels artificial and doesn't offer as much feedback as conventional steering.

Our test car came with the standard electric power steering — which we found quick and responsive — so we cannot report first-hand on the DAS system. But the downside to forgoing the Direct Adaptive Steering option is that it comes bundled with the Deluxe Touring Package, which means you will also have to forego such desirable options as power tilt-and-telescoping steering wheel, Nissan's outstanding Around View Monitor with Moving Object Detection, front and rear paring sensors, and rain-sensing windshield wipers.

On top of that this forty-thousand dollar plus car, as configured, is without a blind spot monitoring system and the rear view camera is missing a cross-traffic alert scheme.

The Q50's interior is well designed and attractive with quality materials throughout. The dash is dominated by a dual central touchscreen that control most of the systems. The new center stack has hard buttons down the side of the second screen for controlling climate functions. Radio controls are not so handy, but a six-preset configuration looms large on the screen and is easy to use while under way.

The Q50 is offered in base, Premium, Sport (Q50S) and Hybrid trim levels and in rear-wheel or all-wheel drive. Starting price for the base model is $38,055. The Premium trim begins at $40,905, the Sport at $44,555, and the Hybrid at $47,705. All-wheel drive adds $1,800 to all models.

Standard features on the base model are generous including keyless entry and ignition, cruise control, dual-zone climate control, leatherette upholstery, eight-way power front seats, tilt-and-telescoping steering wheel, rearview camera, the twin touchscreen displays, Infiniti's InTouch infotainment system with voice controls, Bluetooth connectivity, and a six-speaker sound system with CD player, satellite radio, iPod interface and two USB ports. There are several desirable and worthwhile packages available on all trims above the base model including Navigation and Technology.

Our Q50S test car came exactly the way we would equip it if we were investing in the car — excluding the Direct Adaptive Steering, but including the non-run-flat performance tires — and that's probably why Infiniti in providing that model for journalists. The Q50S starts at $44,555 and the bottom line on our test car was $47,755 with the navigation and the tire options.

Essentials
Base price: $38,055; as driven, $47,755
Engine: 3.7-liter V6
Horsepower: 328 @ 7,000 rpm
Torque: 269 foot-pounds @ 5,200 rpm
Transmission: 7-speed automatic
Drive: rear wheel
Seating: 2/3
Wheelbase: 112.2 inches
Length: 189.1 inches
Curb weight: 3,713 pounds
Turning circle: 36.7 feet
Luggage capacity: 13.5 cubic feet
Fuel capacity: 20 gallons (premium recommended)
EPA rating: 29 highway, 20 city, 23 combined
0-60: 5.2 seconds (Motor Trend)
Also consider: BMW 3-Series, Cadillac ATS, Acura TL

The Good
• Muscular V6 engine
• Attractive, user-friendly interior
• Cutting edge technology

The Bad
• Tire option necessary for best results

The Ugly
• Direct Adaptive Steering is a work in progress