What is a damper valve stack?
A damper (or shock absorber) turns motion into heat by forcing oil through a valve. The valve itself is a stack of very thin steel discs called shims, sitting over the holes in the piston.
When the piston moves, the oil pushes against the shims and bends them open a little. The harder it is to bend them, the more force the damper resists with.
Why does the shape of the curve matter?
A suspension sees two kinds of motion: slow body movement and fast bumps. The shim stack sets how the damper behaves at both, so the same stack can be tuned for comfort or for control.
Drag the sliders to feel the trade-off. Adding shims or thickness lifts the whole curve; preload rings lift the low-speed end most, which changes how planted the car feels.
1. Set the shim stack
The three sliders set the stack: how many shims, how thick each one is, and how many preload rings sit on top. Together they decide how stiff the valve is.
2. The piston pushes oil
As the rod moves the piston through the oil, it forces that oil towards the passages in the piston face. The oil has to go somewhere, and the only way out is through the valve.
3. The shims bend open
Oil pressure lifts the edges of the shims just enough to let oil past. A stiff stack resists that bending, so it takes more pressure to open and bleeds less oil.
4. Force scales with speed
The faster the piston moves, the more oil is pushed per second and the more the shims deflect. That is why damping force climbs with piston speed, but flattens as the shims open further.
5. The setup shapes the ride
Low-speed force sets body control and how the car takes a corner; high-speed force sets how sharp bumps feel. The verdict readout names the balance your settings produce.
What is a shim stack, in plain terms?
It is a pile of thin steel discs that sits over the piston's oil holes. Oil pressure bends the discs open, and how much they resist sets the damping force.
Why does adding shims make the damper stiffer?
More shims make the stack harder to bend, so it takes more oil pressure to open. The stiffer the stack, the higher the damping force at every piston speed.
What do the preload rings change?
Preload rings press the stack closed before any oil pressure arrives. That mostly raises force at low piston speed, which is what you feel as body control.
Why is damping force not a straight line against speed?
Damping rises roughly with speed to the power 0.75, not in a straight line. It climbs quickly at first and then flattens, which is why the curve bends.
Does a stiffer stack always feel better?
No. A very stiff stack can feel harsh over sharp bumps and can hurt grip. There is a trade-off between control and comfort, which is what the tuning verdict hints at.
Are the low- and high-speed points real?
They are two representative piston speeds, 0.3 m/s and 2.0 m/s. Real dampers are tuned for both, because a suspension sees slow body motion and fast bump motion.