Explained in detail: Adaptive dampers and how they work

FSD dampers are slightly better than standard ones, but are no match for proper electronically controlled adaptive ones.

BHPian d3mon recently shared this with other enthusiasts:

The dampers are electronically controlled, adjusting every few ms.

The FSD dampers are slightly better than standard ones, but are no match for proper electronically controlled adaptive ones.  Technical documentation on these is hard to come by because car companies are highly secretive about this kind of stuff. But let me try to summarize what this adaptive damping is all about.

First, let me introduce what a damper dyno is. It shows the measured resistance (force) that a damper applies to the spring in order to control the body movement. If you have a low damping force (underdamped), the body would continue oscillating for a very long time after encountering a bump. And if the damping force is too much (overdamped) , the spring would not get enough compression, and a lot of impact would be transferred to the body, and the wheel may even lift off the ground, losing traction. This would feel make the car feel quite skittish.

With the right amount of damping (critical damping), the spring compresses once, and then just settles back to the original position as quickly as possible, without going up and down multiple times.

Needless to say, the critical damping value required at every moment to control the wheel and the body motions changes constantly. The force required to control a large bump at high speed vs a small bump at low speed are vastly different. Fixed dampers do provide varying forces which changes with the speed of motion of the damper (up / down) in compression / rebound.

But these are inherently limited in which speeds or what kind of driving they are tuned for.

Many performance upgrades like the Bilstein B6 offer an increased damping force across the entire velocity spectrum, by a factor of about 1.5 to 2x.

Remember this number. Compare the B6 vs the BMW OEM in the graph below and you'll make that out fairly easily.

That lends to much better body control on the highways, but every single review of the B6 put on F30s (plenty of them on TBhp) mentions that the ride gets quite busy at city speeds. This is the inherent limitation of fixed dampers - you can't have both a pliant and comfortable ride, and also good highway manners.

Enter adaptive dampers. The below image from Porsche is the closest that I could find that shows what electronically controlled adaptive damping can do.

Here, you can see the damper dyno for compression and rebound is no longer just a straight line, rather it's an area. The top and the bottom lines for compression / rebound are the upper and lower limits of the characteristic curves that can be called upon by the vehicle dynamics ECU at a (few) millisecond's notice. Which just means that there's a lot of latitude that the ECU has in what kind of forces to apply via the damper.

If you look at actual values for the forces at a particular damper velocity, let's say 0.5m/s, you can see that the rebound force produced by the dampers can be varied between around 1500 to almost 6000N. That's a spread of 4x! And the compression stage goes from about 1000 to 3000N, which is about 3x.

Compare that to the 1.5x-2x FIXED factor provided by a suspension upgrade like B6, and you'll start realizing what a game changer these dampers are.

It's literally like having a stock suspension + B6 or B8 + softer than stock suspension all at the same time, available for the car to optimize as per the driver's request and the road conditions.

On top of all of that, all 4 dampers are independently controlled, based on the individual bumps encountered by each wheel. They react differentially (left vs right, or front vs back) in order to control body roll and pitch under braking / acceleration, by instantly stiffening up the damping forces when the ECU detects steering, brake or throttle inputs.

And the mechanism for operation is usually via an electric motor that just turns a valve inside the damper, pretty similar to how a coilover works. Just that the control is electronic, and happens continuously while driving, while coilovers require you to pull over and set it up once. There are zero reliability issues with these dampers, unlike air suspension, where the rubber components naturally degrade over time and have to be replaced periodically.

All this is just theory - please come and experience it yourself. Let's plan a breakfast drive soon.

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