Overall, the Infiniti Q45 represents an excellent effort that entirely succeeds with its engine performance and handling balance. We enjoyed plenty of seat time in both models, both of which offered distinction and character.
The ride quality is firm yet sophisticated. Compared to the previous generation, the latest Infiniti Q45's four-wheel independent suspension features revised geometry up front, and a redesigned multi-link system in the rear that is lighter and has less friction. Infiniti claims somewhat hyperbolically that the Q45 feels like a car "half its size," and although the Premium model's handling was responsive (with its sport suspension and 18-inch wheels), we had little doubt of the car's size when we were cornering. Still, when you pitch this big baby it stays with you. It's easy to control when the tires squeal, and doesn't fight you for control. We found the speed-sensitive power-steering rate to be a bit insensitive, reacting slowly when the input was subtle, as on long curves.
In terms of ride quality, the suspension levels out the bumps really well on a straight road. But when the bumps get more complex, and come in turns, the suspension seems to dip at the corners and sides, and you get subtly rocked. This feeling could be from the limited seat bolstering, however.
The Premium model's adjustable suspension can be set in a Sport mode, but we couldn't feel much difference between the Normal and Sport modes when the driving was sporty. Normal mode was firm enough to be good in the twisties. But we did feel a big difference over sharp bumps. You don't want to be in Sport mode over potholes or at slow speeds. So we couldn't find much use for Sport. If Normal were softer, then both modes would be used.
Run-flat tires (17-inch only) are also available. Nissan says they can run 50 miles at 55 mph after a puncture. They might significantly change the feel of the ride, making it harsher, but this is speculation as we have not tried them out. Run-flat tires have very stiff sidewalls, bit tire makers continue to improve the ride quality.
The 340-horsepower engine really starts to kick ass at 3000 rpm. A computer (Electronic Torque-Demand Powertrain Control) keeps much from happening from a dead start, but at 3000 rpm it sets the engine loose. The mid-range response is great, with a whopping 333 pounds-feet of torque at 4000 rpm. This year's numerically higher 3.133:1 final-drive ratio makes the Q45 feel livelier still. The engine makes a wonderful growl, which you can mostly hear only with the window down. It is, after all, a luxury car.
On paper, the Q45 wins the power-to-weight race against the BMW 540i and Lexus LS430. The Infiniti's 32-valve engine features continuously variable valve timing, a variable flow intake manifold, titanium valves, microfinished camshafts and crankshaft, and lightweight pistons.
The sweetest thing about the Infiniti Q45 is its full-throttle upshifts at about 6500 rpm. The current model's five-speed automatic transmission is 50 pounds lighter than the four-speed it replaced, with the extra gear improving acceleration and fuel mileage. The new transmission is also designed to handle more power. On the downside, it shuddered on us at slow speeds, upshifting into second gear, as if it were confused by a throttle signal ("What does this guy want?"), which may have been the case.
The manual mode is to the right of the Bird's Eye Maple shift lever, and moves forward and back, engaging with a satisfying click. But "manual" is rarely if ever taken literally with transmission designer/programmers, and we found the program shifting more than we wanted it to, overriding our wishes and plans, so we pretty much stopped using it, and just let the transmission shift where it wanted to. It did fine, but we were disappointed that manual gear selection had been offered, then effectively taken away from us. We wanted to play more.
The four-wheel anti-lock vented disc brakes are big. The system includes Electronic Brake-force Distribution (EBD), which balances front and rear brake force depending on the load. Passengers and cargo upset the brake balance in any car, and EBD is designed to correct this, stopping the car quicker and more controllably. There's also Brake Assist, which reduces pedal effort under hard braking. It's a simple mechanical system that reduces pedal pressure during panic stops when ABS is activated, unlike the German electronic systems that take over your brake pedal, presuming to know better than you what you want your car to do. Infiniti says that during testing of the system, stopping distances were reduced by 10 percent to 15 percent, which can make the difference between hitting that rear bumper and not hitting it.
Vehicle Dynamic Control reduces power and applies the brakes at individual wheels when traction is lost at any wheel. We pushed the Infiniti Q45 until the VDC corrected us, which it did subtly on a hard, sharp curve with loose gravel over pavement; we would have slid a few feet, but VDC caught the car. There's also a traction control system, which we liked better than the Mercedes system because it doesn't cut the throttle so radically or for so long.
Infiniti also offers Intelligent Cruise Control, which will maintain a set distance between your Infiniti Q45 and the car ahead of you. Look ma, no feet. It works very well, but you still need to pay attention to your driving.
