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Discussion Starter #1 (Edited)
ZF Sachs' Nivomat self-leveling monotube shock is a proven and inexpensive way to improve vehicle stability.

ZF Sachs Nivomat shock absorber system reduces the trade-off when tuning the suspension. With Nivomat you can tune for the best optimal ride in the un-laden condition knowing that the system will optimize the vehicle in the fully loaded state.

Nivomat (from the French Niveau, meaning of a higher class or different position and mat, as in automatic) is a monotube designed shock absorber that provides a mechanical self-leveling feature utilizing the energy that is generated by the relative movement of the axle and body when driving.

Nivomat is a semi-supporting system working in combination with a mechanical spring. The Nivomat shocks are only mounted on the rear where most of the additional weight is located.

Nivomat looks like a standard shock absorber with a piston rod with damping valves at the end, an outer tube and a cylinder tube. Several components are added to provide the leveling function. Two reservoirs are contained in the outer tube, an oil reservoir (or low pressure reservoir) and a high pressure chamber. Inside the piston rod is the pump chamber (with inlet and outlet valve) and the pump rod, which serves as a height sensor or regulator and a release bore which releases the pressure after the vehicle has reached level.

A load initially causes static compression of the vehicle's suspension. Once the vehicle begins to move, the pump is activated by the relative movement of the body.

Extension of the piston rod causes oil to be drawn through the inlet valve into the pump. Compression then pushes the oil through the outlet valve into the high pressure chamber. The pressure in the oil reservoir decreases as the pressure in the high pressure chamber increases. The increasing pressure acts on the piston rod and raises the vehicle at a continuous rate.

Once the vehicle has reached optimum height, oil is no longer drawn in. The height regulator opens a bypass between the high pressure chamber and the pump chamber preventing oil from flowing out of the oil reservoir.

When the vehicle is unloaded the vehicle begins to rise. The height regulator opens the release bore. Oil flows out of the high pressure chamber into the oil reservoir, the pressure drops in the high pressure chamber and the vehicle lowers to the initial height.

"It takes very little input to actuate the pump," says Hunt, "about plus or minus a millimeter is all it needs, so even on smooth roads the Nivomat pumps up quite quickly."

But the Nivomat system doesn't just level the vehicle under load. As the load increases, the pressure inside the shock increases oil is displaced from the reservoir to the inside of the unit, compressing the gas volume. This creates a progressive increase in spring rate and damping with little or no change to ride frequency.

"At a high GVW or max load, the ride frequency would be almost the same as curb position, but would never go as low as a conventional suspension," says Grasse.

"Rear air leveling is the direct competitor to this product," says Hunt. "But with either a conventional suspension or air-leveling suspension you don't get a significant increase in spring rate with load like you do with Nivomat."

Grasse adds that Nivomat offers significantly improved roll stability at gross vehicle weight without a penalty to curb weight. On a Chevrolet Suburban the Nivomat system adds 442 Nm/deg roll rate.

"A very noticeable improvement in roll stability," says Grasse.

ZF Sachs currently supplies Nivomat shocks to nine OEMs in Europe and North America, including DaimlerChrysler, Ford, Fiat, General Motors, Jaguar, Kia, Mitsubishi, Opel, Saab and Volvo. The system is available on the GM Suburban and Tahoe as part of a towing package. Hunt says that if there is a downside to the system it's that Nivomat is rather stealth to the user. There is no compressor sound and dealers don't often tout the systems capabilities.

"It seems," adds Hunt, "that people aren't realizing what they're getting."

Nivomats are typically found at the back end of minivans, wagons and SUVs -- vehicles that see a lot of rear axle load when all the people pile in or when a trailer is latched on. Nivomats are very high pressure monotube dampers, but they also function as adjustable rate springs that have internal ports that vary the amount of support they give based on how far the suspension is compressed. If you add load and compress the suspension, the motions associated with driving "pump" them up using pressure stored in an internal accumulator. Unloading the trunk of a car with "pumped" Nivomats will result in an overly-raised "ass-up" attitude, but that simply exposes a second internal port that drains fluid back into the accumulator until equilibrium is restored.

Sound complicated? It is. All you have to know is that Nivomat load leveling shocks are self contained, with no compressor or external connections of any kind.
In a typical Nivomat installation, only 65 to 75% of the rear spring duties are carried out by the actual coil springs; the remainder is carried-out by the Nivomat unit itself. What that means is that you can't simply toss-on any aftermarket shock in an attempt to tune your suspension because this Nivomat is an essential part of the spring force that supports the rear of the car. It has to stay here at all costs unless you put on new springs that can go it alone without Nivomats.

All of this begs the question: What is a pair of load-levelling shocks doing on the back of a Dodge Challenger?

Turns out that Nivomats are very good at combatting axle hop during hard drag-style launches. They help put the power down when you drop the clutch.

So that's a second reason why you want to leave these babies alone if you throw aftermarket "upgrade" parts at your suspension. And when it's time for new shocks on an unmodified car, you'll need to buy new Nivomats.
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