Chicken Soup for the Suspension

You've heard of the book Chicken Soup for the Soul. It espouses fundamental upgrades to one's lifestyle and philosophy that enhance spiritual well-being.

Extend that idea to what Tenneco Automotive is seeking with its new Monroe Reflex shock absorbers: an elemental "fix" for suspension engineers' most vexing problem, the traditional damping-calibration tradeoff between firm, sporty handling and genuine ride comfort. There's always been an implicit compromise between a state of suspension tuning that provides crisp handling and body control and one that offers plush ride characteristics.

"The ride-control compromise is a graphic equation that simply says that for each measure of increased control, the vehicle driver will experience an equal decrease in comfort," says Terry Heffelfinger, Monroe's chief engineer, aftermarket engineering.

What Mr. Heffelfinger and his Monroe engineers sought was a simple way to deal with that "ride control compromise." What they delivered was the Reflex shock absorber, which incorporates a valve technology that briefly "releases" the firm damping designed into the shock when the vehicle hits a bump or pothole. As soon as the large bump or series of bumps is over, the Reflex shock returns to the normal, firmer-than-average damping characteristics that provide superior handling and body control.

This, of course, has been tried virtually since suspension was first adopted for passenger vehicles. Lately, advanced electronics have tempted engineers to rig all manner of complex "active" suspension designs in the crusade for firm handling and cushy ride all in one suspension - all of which, for the most part, didn't work. Recent advances, like Mercedes-Benz's Active Body Control (see WAW - June, '99, p.44) have moved closer to suspension nirvana, but electronically controlled systems remain complicated and decidedly expensive.

Monroe wanted the simpler "chicken soup" fix. The Reflex shock features "Impact Sensor Technology," the company's catch phrase for a simple but elegant new valving system and improved materials. Most important is the new Reflex valve system: On even surfaces, a floating intake valve in the base valve - located in the shock chamber - stifles fluid flow, which delivers that firm body control.

Hit the bump with 1.5 g or more of vertical wheel acceleration, though, and in 15 milliseconds the compression of the shock causes a second spool valve to open, exposing extra fluid passages and also passing fluid through the spool valve itself. This has the effect of "softening" the damping instantly; if frequent bumps occur, the spool valve remains open. When it's all over, the spool valve immediately shuts, and all that extra fluid now must flow through the "normal," more-restrictive channels, returning the firm-control effect.

Monroe convinced Nissan Motor Co. Ltd. chassis engineers, apparently, because the company was awarded an OE contract to supply the Reflex shock absorbers for Nissan's '00 Altima SE.

A hard-charging test of the Reflex-equipped Altima SE at Michigan's serpentine Waterford Hills race track convinces us, too. Even in SE trim, Altima is not meant to be an all-out sports sedan, yet the Reflex shocks help make the new Altima an entertaining handler - much more so than the previous model, which most would consider was tuned for the "ride comfort" side of the above-mentioned ride/handling tradeoff. More satisfying, though, is the enhanced body control during normal driving, where with many cars and sport/utility vehicles (SUVs), nonsensically excess body roll makes even turning corners on city streets at nominal speeds a wearying experience.

The Reflex shocks are offered for SUVs and light trucks, too, and deliver a meaningful upgrade in particular for SUVs, given their typical propensity for ride height-induced body roll.

Monroe says it has tested a previous-generation Grand Cherokee, upon which the Reflex shocks improved body roll by 12% in a J-turn; just as satisfying to those sick to death of the "pitch" always present in SUVs, company engineers report a marked 18% reduction in braking-induced pitch.