Bilstein Shock Cover - The Big Cover-Up - Tech

So in a sense this design is even more traditional than a T-10 transmission, small-block anything, or Ford 9-inch axle. At the same time, they're more sophisticated than most other damper designs, including many of the trick-looking billet ones (most are nothing more than twin-tube dampers with trick-looking bodies, according to Duck).

As compelling as they are, those aren't the only reasons you should consider Bilstein dampers for your next car. A number of smaller stories-sidebars, we call them-outline the other virtues of the design. Take the time to read through them. You may just come to the conclusion that there really is more to a damper than just another pretty face ... or body.

Performance Under Pressure
If you've paid attention for the past, oh, 30 years you've heard about gas-charged shocks (dampers). Gas charging increases the pressure exerted on the oil inside the damper, but do you know why it's a big deal?

All fluid has a boiling or vapor point. But that point isn't etched in stone; it varies considerably depending on the pressure exerted upon the fluid. Water's boiling point varies by about 3 degrees F per pound pressure. At sea level that's 212 degrees; at Pike's Peak, it's 187. Inside a cooling system under 13 psi greater than atmospheric pressure, it's about 243 degrees F.

We typically don't think of oil as boiling, but it does. In fact, oil can boil spontaneously at room temperature as it passes through the piston head. Whether called cavitation or aeration, the force of millions of these little bubbles imploding as the fluid pressure equalizes can generate enough heat to melt the seals out of a damper.

To combat this, Bilstein (and tuners like RCD) pressurize the fluid within the dampers to around 200 psi. As a result, the damper maintains its effectiveness at higher speeds and over rougher roads. It's a feature that reveals itself especially on cars with stiff-sidewall bias-plies or low-profile radials.

Right, Right Out Of The Box
Within the past generation little knobs started appearing on dampers intended for the hot rod, street rod, and custom-car market. By simply turning them, those knobs could tune a damper to suit a particular application. At least that's what manufacturers proclaimed.

To a market conditioned to shop for dampers at the local parts store and choose them on their physical dimensions, adjustable dampers were a bit of an improvement. A '76 Cadillac Fleetwood damper might fit a buggy-sprung Model A roadster, but it'll likely make the car ride like a buckboard. So at least the adjustability allowed these new dampers to perform adequately on our cars.

But when did you ever describe your hot rod as adequate? Most adjustable dampers are nothing more than standard twin-tube pieces that rely on bleed valves exclusively. Turning the knob on one selects how many of those bleed valves operate. The damper may be adjustable, but in the end it's just as limited as any fixed-rate damper that's tuned to behave a certain way. Tuned one way it might ride well at lower speeds or smooth roads but may rattle your kidneys on rougher roads or at higher speeds.

Chances are you'll never see a tuning knob on a Bilstein. It's because Bilstein and the independent tuning companies like RCD build dampers for specific applications. While Bilstein maintains a catalog of part numbers for most cars, RCD filled in the gaps with more specific applications. So if you need one for, say, a big-block-powered '57 Chevy passenger car or an F-100 with a GM clip, RCD has you're covered. It even lists a few off-the-shelf part numbers for various-length dampers, whether bare or coilover, for live-axle cars.