Run-flat tires (17-inch only) are available ($400). 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, but tire makers continue to improve the ride quality. The most responsive handling comes from the Premium version with its 18-inch wheels and tires.
The engine and transmission are very responsive. The Q's V8 engine provides lots of power: 340 horsepower. That compares with 290 horsepower from a Lexus LS 430. The 4.5-liter V8 feels particularly strong starting at 3000 rpm. The mid-range response is great, with a whopping 333 pound-feet of torque at 4000 rpm. Its full-throttle upshifts at about 6500 rpm are exciting. A final-drive ratio of 3.13:1 adds to the Q45's lively character. The 32-valve, four-cam engine makes a wonderful growl, which you can mostly hear only with the window down. This is, after all, a luxury car.
Shifting is silky smooth. The five-speed automatic transmission was very responsive, so we preferred to leave it in Drive. However, it does offer a manual mode: From Drive, push the wood-trimmed shift lever into a separate gate to the right, then move it fore or aft to change gears. The shifter engages with a satisfying click. The system is programmed to override the wishes of the driver when those wishes don't compute, however.
The four-wheel anti-lock vented disc brakes are big, over 11 inches front and rear. 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, as does the forward shifting of weight as the car stops, 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. Infiniti uses 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 its system, stopping distances were reduced by more than 10 percent, which can make the difference between hitting and stopping before hitting the rear bumper in front of you.
Vehicle Dynamic Control reduces power and applies the brakes at individual wheels when traction is lost at any wheel. 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-Benz system because it doesn't cut the throttle so radically or for so long.
Intelligent Cruise Control (included in the Premium package) will maintain a set distance between your Q45 and the car ahead of you, slowing your car down when the car ahead slows down. Look ma, no feet. And if you close on the car ahead too quickly, the Preview Braking feature pre-pressurizes the Brake Assist system, optimizing brake response when you do finally wake up and step on the pedal. It works very well, but we recommend that you still pay attention to your driving. Next Page