Quick! For one million dollars, name the single part that’s shared by the Cadillac XLR, Chevrolet Corvette (F55 or ZR1), Acura MDX, Ferrari 599, and Audi TT! Stumped? Well, it’s the shock absorbers.

Since 2002, the suspension division at Delphi has been refining and expanding its line of magnetic rheological shock absorbers (MRSAs), which are simple in concept but complicated in execution, requiring lots of iterative software development and Delphi’s engineers working hand-in-hand with development engineers from each client company.

MRSAs have suddenly become popular with a number of manufacturers because they are relatively straightforward in construction and they work much faster than conventional, hydraulic shock absorbers. They use a special fluid composed of oil and microscopic, uniform iron particles. Acted upon by an electromagnetic force, the fluid becomes a semisolid and offers greater resistance to the moving parts of the shock absorber and suspension, whether a wheel has dropped into a pothole or been jounced upward by a speed bump. The amount of change in the behavior of the fluid is directly proportional to the amount of electrical current applied, usually in a range between zero and five amps. That’s what differentiates the MRSAs in the Ferrari from those in the Acura.

The suspended-iron fluid is a patented compound devised by Lord Corporation of North Carolina after years of experimentation. In the early stages, the iron filings would settle to the bottom of the chamber when cold, but now the viscosity of the fluid and the uniform particle size have solved that as well as some other problems. Lord also sells the fluid for use in devices as diverse as prosthetics and heavy-truck seat suspension systems.

MRSAs don’t operate in a vacuum, out at the four corners. Instead, an MRSA control system receives constant updates—every millisecond—from vertical acceleration sensors, yaw and lateral g sensors, brake pressure sensors, wheel speed sensors, and wheel stroke sensors, typically about 15 sensors per vehicle. Depending on the information received, the mathematical algorithms tell the system what to do.

When the input force is low, such as while cruising down the highway over good pavement, the shocks behave normally, gently cushioning the suspension’s movements. When the pavement gets rough or when the vehicle corners, dives, or pitches, the computers come into play, instantly assessing the situation and applying more or less magnetic force to the fluid in each shock absorber. The system can stiffen the shocks in about five milliseconds, much faster than conventional shocks can react—about twenty to thirty milliseconds, or four to six times slower than MRSAs. In a curve, the outside shocks go full hard to combat roll while the inside shocks go full soft to preserve a level ride.

Part of the beauty of the system is that each corner of the car is free to act independently, depending on inputs from the road, so that the system becomes a sort of near-active suspension for far less money than a true active suspension would cost.

Most MRSA applications feature normal and sport modes that can be switched by the driver via a dashboard or console button. On some Cadillacs, the driver switches modes via a display-screen selector. Switching to sport mode changes all the MRSA system’s algorithms instantly to provide a much flatter, sportier ride.

The Delphi MRSA system, called MagneRide, was introduced in 2002 on the Cadillac Seville. It appeared the following year on the 50th Anniversary Corvette and was later adapted to the

Cadillac STS, DTS, and SRX, then the C6 Corvette, and most recently the Buick Lucerne—all of which are products of Delphi’s No. 1 client, General Motors.

But the technology quickly expanded to Europe and Japan with Ferrari, Audi, and Acura applications. It was the first time in Ferrari history that the company relied on an American electronics supplier for such an important part on its world-class sports cars.

David Hoptry, marketing manager of Delphi chassis systems and a twenty-one-year Delphi veteran, says the company has a very complete set of tools that allows them to adapt the

MRSA system from vehicle to vehicle regardless of the suspension layout, from a premium sports car to an SUV to a luxury sedan to a performance coupe. He says it usually takes about six months to work out the hardware, installation, and calibration of the system and then about twelve months to get to volume production. Once mounted, MRSA shock units are expected to last the life of the car.

Hoptry says the Delphi MRSA units will be applied to three more passenger cars before the year is out—one European and two Asian vehicles, none of which will be sold here.

He says the company has three manufacturing centers for the MRSA system: in Kettering, Ohio; Krosno, Poland; and Chihuahua, Mexico. With the international expansion, there are now four development centers: in Krosno, Paris, Tokyo, and Detroit, employing about 100 engineers. It looks like they will all be very busy from now on.