Digressive valving, Bilstein COB piston, what does that mean?

Our Spec-S suspension uses digressive valving and it's more than just a marketing buzzword..

Digressive shock valving refers to a damper design where the force builds quickly at low shaft speeds but then levels off, or “flattens,” as the velocity increases. On a dyno plot, this creates a steep initial slope followed by a plateau, instead of a straight linear ramp. This type of valving is intentional—engineers tune the piston ports and shim stacks so that the shock delivers firm control at low speeds, when body roll, pitch, and squat occur, but then opens up at higher shaft speeds to allow the wheel to move more freely over bumps. The result is a suspension that feels both tight and responsive when the chassis is moving slowly, yet more compliant and forgiving when the wheels encounter sharp impacts.

The key benefit of digressive valving is chassis stability without sacrificing ride comfort. Since most handling maneuvers—cornering, braking, and accelerating—happen in the low- to mid-speed shaft velocity range, having more damping force in that region keeps the car planted, reduces float, and sharpens driver feedback. At the same time, because the valving flattens out at higher shaft speeds, the shock doesn’t transmit excessive harshness from potholes, expansion joints, or rough terrain. This makes digressive shocks particularly well-suited for performance street cars, autocross, time attack, and even rally, where the suspension must balance precision control with compliance.

Another advantage of digressive shocks is tuning versatility. By adjusting the crossover point and plateau level, manufacturers can fine-tune how “stiff” the shock feels at low speeds versus how much comfort it provides at high speeds. Enthusiasts who want a car that feels sharp and responsive on smooth tarmac can run a more aggressive digressive curve, while those who want dual-purpose road and track use can select a milder setup. Compared to purely linear or progressive shocks, digressive designs give engineers more freedom to dial in handling balance without forcing the driver to accept an overly harsh ride.

The Bilstein COB piston is where cutting-edge engineering meets real-world performance. Designed with an advanced check-valve system, the COB piston gives your suspension the intelligence to know when to stay firm and when to let go. At low shaft speeds—during cornering, braking, and acceleration—it delivers the tight, controlled feel that keeps your car composed and razor-sharp. But when the road gets rough, the COB piston opens up, absorbing potholes, curbing, and harsh bumps with remarkable compliance. The result? Maximum grip, confidence, and comfort, no matter the surface.

Unlike conventional shock designs that force you to choose between ride quality and handling, Bilstein’s COB piston technology delivers both. It reduces heat buildup and resists fade, ensuring consistent damping performance even under the most demanding conditions—whether that’s a weekend at the track, a rally stage, or your favorite backroad. This is suspension technology born from motorsport and refined for drivers who demand more from their car. With the COB piston, you don’t just get better shocks—you get a smarter suspension system built to perform everywhere!