Everyone is talking about it, but Nissan`s Infiniti division is the first to actually come up with it-active suspension.
Actually, ”active” is something of a misnomer, because the suspension system is designed to keep the driver and passengers inactive when the car goes through the typical jostling that occurs when the tires meet the road.
Active suspension controls vehicle motion-up, down and sideways.
Active suspension is called an ”intelligent” suspension. Special sensors detect any change in body level in order to regulate motion and therefore body position.
The Infiniti Q45 sedan is available with active suspension for the 1991 model year.
Active suspension, like just about everything in today`s cars, relies on computers, sensors and microprocessors to reduce road harshness, smooth out roller-coaster undulations in the road and eliminate body roll in corners and turns-both your body`s and the car`s.
To better understand what active suspension means, we drove the Q45 without, then with the system.
Without active suspension, the Q45 performs well, but you feel the bumps in the pavement and the roller-coaster movement over a stretch of concrete suffering from moisture upheaval. You also lean a bit in sharp turns or bends such as the merger ramp onto or off the expressway.
Active suspension doesn`t mean roads automatically become smooth, as we quickly found after switching into a Q45 with the system.
You are only slightly more cushioned from the force of the blow, as we determined after seeking out rough pavement.
Where the change is most noticeable-actually eerie-is when you approach that exit ramp, the one that stands a few stories in the air and twists sharply to the left to enter Interstate Highway 94.
With active suspension, we took the ramp 10 m.p.h. faster than without it. The reason is the car sits flat in a turn. We didn`t slow down to compensate for body lean, because there was little or none.
What`s it like? Next time you`re behind the wheel, make a sharp right swing down a merger ramp; your body will tilt and lean into that turn, as will the car. With active suspension, you continue to sit upright-no lean-and so does the car.
If there`s a drawback, it`s that you tend to drive a bit faster in those bends in the road. On a ramp leading off the Southfield Expressway onto Dearborn`s Michigan Avenue, we accelerated while the drivers ahead were tapping the brake pedal. While we could go faster, we had to back off the pedal to compensate for those ahead.
It`s similar to driving a four-wheel-drive Blazer or Cherokee in a snowstorm. You can pull yourself through 6 inches of snow but are still at the mercy of the rear-wheel-drive Mustangs and Camaros slipping and sliding and blocking the path ahead of you.
There`s another time when active suspension will boggle your mind-the simple act of braking. At 40 or 50 m.p.h., when you apply the binders, your body will lurch forward. The shoulder harness retracts to keep you from kissing the steering column. Your hands grip the wheel hard to keep your body in place as it moves forward.
With active suspension, at 40 m.p.h. you apply the brakes and rather than nosedive, you move down in the seat. It`s as if someone pushed the power seat button marked ”down.”
Rather than move toward the wheel, you stay put, only now you`re an inch lower in the saddle.
Flat corners and turns and downward rather than forward movement when braking mean you have total control over the car in those situations in which overdriving can get you in trouble.
The system is so good when it comes to driver control that the folks from Infiniti feel compelled to issue warnings.
”It`s not a magic carpet ride,” insists Peter Harris, national product manager for Infiniti and the guru in charge of engineering for the luxury car line.
”We purposely designed some feedback into the wheel so you will continue to feel the road surface,” he said. ”Harshness is reduced but not eliminated.”
We agree. You`ll have a difficult time telling whether a car has active suspension just by driving a few miles on a rough road.
”Where you really feel the motion control of active suspension is when the car sits flat over wavy roads and in sharp turns,” Harris said. ”The floating sensation and feeling of motion you get in most cars is what makes kids carsick on those long rides.
”The key benefit with active suspension is control over motion,” he added.
”In corners, the inexperienced driver will compensate for lean and roll by moving the steering wheel. With active suspension, the suspension adjusts for you.”
Harris said Infiniti could have dialed in an even softer ride ”and even flatter handling, or could have made the car body tip in a corner like a motorcycle. But we wanted to give the driver a seat-of-the-pants warning to know he was reaching the limits of tire-holding capability.
”We dialed in just enough road feel, just enough lean in corners and turns so that the driver would feel something and not abuse the system.”
A hydraulic pump activates the suspension magic. Harris said the pump`s oil and filter must be changed every 60,000 miles to keep the system functioning properly. The pump holds a little more than 4 quarts of oil.
A disadvantage of the system, other than remembering the oil and filter change, is that it can drain about 5 horsepower from the engine in tough maneuvering, which translates into about a 2 mile-per-gallon loss in fuel economy.
The Q45 already carries a $500 gas guzzler penalty for failing to obtain 22.5 m.p.g. city/highway combined mileage from its 4.5-liter V-8. The rating is 16/22. With optional active suspension, add $550 to the guzzler penalty, for a $1,050 tax because of its 14/20 rating.
One side benefit is less wear and tear on tires, because the car sits flatter, meaning the patch of steel-belted radial that meets the road sits flatter, reducing the side-to-side movement that causes wear.
The Q45 offers antilock brakes as standard, but active suspension is a $4,000 option, which includes the $1,050 guzzler tax.
Traction control is a $1,500 option. Traction control prevents wheel slippage while the vehicle is moving. But active suspension and traction control can`t be combined yet.
”We`re working on combining the two for 1992, but I can`t guarantee we`ll have it by then,” Harris said.
Active suspension provides what might be described as a ”calm” ride on dry roads, but it`s not designed for ice and snow the way traction control is. The Q45 starts at $39,000 for 1991, up $1,000 from `90.
William Bruce, Infiniti general manager, said he expects 15 percent of all Q45 buyers will opt for active suspension.
”The market will tell us if people want more,” he said.
