Overall, the Infiniti Q45 is an excellent effort that entirely succeeds with the engine and handling balance. We got plenty of seat time in two separate models, both of which offered distinction and character. The ride quality is firm yet sophisticated. The four-wheel independent suspension features revised front geometry, and a redesigned rear multi-link system that is lighter and has less friction. Infiniti hyperbolically offers that the Q45 feels like a car "half its size," and although the handling was responsive (with the Sport package, including 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. You can push it until after the tires squeal, but it doesn't fight you for control. We found the speed-sensitive power-steering rate to be a bit insensitive (slow-reacting) when the input was subtle, like 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 corners, 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 suspension can be set in a Sport mode, but in the two cars we drove, we couldn't feel much difference between the Normal and Sport mode 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.

New run-flat tires (17-inch only) are also available. They might significantly change the feel of the ride, making it harsher, but this is speculation as we have not tried them out. Earlier run-flat tires had very stiff sidewalls, and tiremakers continue to improve the ride quality.

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The new 340-horsepower engine really starts to kick ass at 3000 rpm. The Car's Own Brain (Electronic Torque-Demand Powertrain Control) keeps much from happening from a dead start, but at three grand the powertrain is set loose. The mid-range response is great, with a whopping 333 foot-pounds of torque at 4000 rpm. The engine makes a wonderful growl ("the sucker roars," said our taped notes), which you can mostly only hear with the window down. It is, after all, a luxury car.
The Q45 will do 0-60 in just 6 seconds and the quarter-mile in just under 15 seconds. Its horses carry it to first place in the power-to-weight division, against the BMW 540i, Mercedes-Benz E430 and Lexus LS430 (and its base price is lowest, by $700, $2000 and $3500, respectively). Technically, the new 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 Q45 is its full-throttle upshifts at about 6500 rpm. The new five-speed automatic transmission is 50 pounds lighter than the four-speed it replaces, 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 lever, and moves forward and back rather than side-to-side, 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 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 beefy. (Fronts are 11.4 inches by 1.1 inches thick, rears measure 11.5 by 0.6 inches.) The system includes Electronic Brakeforce Distribution, 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 the car to do. Infiniti says that during testing of the system, stopping distances were reduced by 10 percent to 15 percent.
As for the Vehicle Dynamic Control, which takes over the throttle and brakes at individual wheels when traction gets dicey … we pushed the 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 is also offering more of the technological future, with Adaptive Cruise Control, which will maintain a set distance between your Q45 and the car ahead of you. Look ma, no feet.