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The Infiniti FX is designed to be driven enthusiastically, borrowing its chassis architecture from the rear-drive Nissan 350Z and Infiniti G35. Rather than an SUV, we'd call it a fine luxury sport wagon with a higher seating position. We should note that it has more interior space than the sport wagons can offer, and we think it is also more exciting to drive than most of them.
Plant the V8-powered FX45's accelerator to the floor and you'll be rewarded with a healthy hot-rod roar. As revs rise, the sound becomes a higher-pitched hum. Brisk acceleration makes the big FX feel athletic and nimble. You get the feeling you can pass anything in front of you. And Infiniti's design objectives come more clearly into focus.
The Infiniti FX45 offers comparable acceleration performance to the Porsche Cayenne S, managing the sprint from 0 to 60 mph in slightly more than 6 seconds.
The V6-powered FX35 is no slouch, either. It launches impressively from a stop, largely because it has substantially more horsepower and torque than most other six-cylinder SUVs. There's as much oomph here as most owners will ever need. We found its acceleration performance entirely satisfactory. The V6 engine that powers the FX35 is the same engine used in the Nissan 350Z sports car. It's powerful, giving the Infiniti FX35 responsive performance. While driving the FX35, we never found ourselves wishing for the more powerful FX45.
Granted, the step up to the V8 is noticeable, particularly when you stab the gas at, say, 60 mph. The Infiniti FX45 will rocket to 80 at a much greater rate than the FX35. However, with gas prices rising, one must note that the V8 also chugs fuel at a much greater rate, reducing range between fill-ups by anywhere from 25 to 75 miles, according to the EPA's numbers. Both FX models are electronically limited to a top speed of 130.
All this power is managed with sophisticated electronics with names that sound like alphabet soup. The ATTESA E-TS (Advanced Total Traction Engineering System for All Electronic Torque Split) all-wheel-drive system improves handling in limited traction situations due to its optimum 50/50 front/rear torque distribution, which can shift rearward up to 0/100 when conditions require. The system provides good starting traction and stable acceleration in snow-covered or off-road situations, since it always starts off with the torque split 50/50.
The VDC (Vehicle Dynamic Control) electronic stability control system reduces engine output and/or lightly applies braking force to individual wheels when entering a corner too fast. It engages so gradually that we couldn't detect when it was working.
The Infiniti FX suspension is stiff, reflecting Infiniti's decision not to make this SUV an off-road vehicle. With its limited travel and taut feel, the suspension gives the FX excellent handling on smooth, winding roads. However, we noted that the stiff suspension made the FX less than ideal when traveling any distance on an unpaved road. And while the FX offers a high ground clearance of 7.6 inches, it doesn't have skid plates, underside armor, or the long travel and compliant suspension tuning of a true off-road vehicle.
On tight and sweeping corners, however, the body stays incredibly level, which is the plus side of its stiff suspension. We drove it hard, as we would drive a sports sedan. Understeer, or the sliding of the front tires that is the default skid condition in most vehicles, begins very gradually when you aim the Infiniti FX into a corner, and the front wheels continue to push only slightly until you get near its very high cornering limits. If really pushed, the VDC allows a slight amount of power oversteer while cornering (a satisfying fish-tail effect in the rear), although we were never able to break the mammoth rear tires completely loose. As in the 350Z, the FX's steering is quick. It doesn't feel as telepathic as a Porsche's, but it doesn't feel light and loose like that in many SUVs, either.
The brakes are good. The Infiniti FX45 remains confident and stable under heavy braking, allowing us to drive it very quickly, without any scary moments, on twisty roads. However, braking quickly reminds the driver of how much mass has to be slowed down. A vehicle as heavy as the FX, but also as nimble, can require acute awareness from the driver, because it feels so well-mannered that it's easy to forget how fast it's going and how heavy it is. The best brakes and most sophisticated stability electronics devised can not defy the laws of physics.
Still, the Infiniti FX offers a new braking trick that until recently was reserved for the most expensive luxury sedans. Called Preview Braking, it comes on FXs equipped with the traffic-sensing Intelligent Cruise Control system. The radar sensors that manage the active cruise control can sense when the FX is closing on an object at a high rate. When they do, the system pre-pressurizes the brake hydraulics before the driver even touches the pedal; that speeds brake activation by critical fractions of a second once the driver's foot and the pedal meet.
With their sports supensions, the FX45 and the FX35 with the Sport package are reasonably comfortable in freeway driving. There, the FX rides smoothly enough and feels relaxed. The Infiniti FX45 cruises at 80 mph in fifth gear with the engine turning a low, quiet 2,800 rpm. The cabin is quiet and isolated enough for delicate cell phone conversations, but it's not the serene environment of a true luxury sedan.
The FX35 without the Sport package rides more smoothly and more pleasantly. It's still plenty nimble and quick and fun to drive. But its suspension is slightly more compliant, more comfortable in most situations, and its higher profile tires take some of the crack out of bumps and expansion joints. However, even the FX35's suspension is on the firm side and the ride gets a little bumpy on rough streets at low speeds. Some drivers prefer the ride quality of the FX35 over that of the FX45.
The Lane Departure Warning system recognizes lane markings through a small camera mounted behind the rearview mirror. Above 45 mph, a microprocessor uses the camera's signal and the vehicle's speed to calculate both the distance between the FX and the lane markings, and the lateral velocity at which those markings are getting closer. The system sounds a buzzer if it decides that the vehicle is wandering out of its lane. The system is temporarily disabled by the turn signals, and it can be shut off entirely with a manual cancel switch. It automatically resets itself when the vehicle is restarted.
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