A well-matched damper and spring combination can give a car razor-sharp handling without the harsh ride that sometimes come with aftermarket suspension kits. The key to getting the best of both worlds is to have dampers that are tuned or "valved" to match the "stiffness" or rates, of the springs.
Striking the perfect balance between spring and damper rates isn't a simple matter. The more reputable suspension tuning companies spend huge amounts of time and money continually developing, testing and refining their products until they get it just right. When they finally get everything right, the payoff comes in the form of a coilover kit that strikes that elusive balance of precise handling and good ride quality that's so important in a track/street car.
One of the nicest things about many aftermarket coilovers is the wide range of adjustability they offer, including the option of swapping out the springs for stiffer or softer ones or having the dampers revalved. Leaving the coilover in its original configuration will best suit the vast majority of people, but there are cases where the standard spring and/or damper rates just might not cut it.
For example, say you spend lots of time at triple-digit speeds and want a little more high-speed stability, or maybe your roads are covered with pot holes and you need a plusher ride. Or maybe you just want to experiment a little: Dial in some oversteer with some stiffer springs in the rear, maybe eliminate some excessive oversteer by installing softer springs in the rear... whatever you want, you can have by revalving or swapping springs.
Damper rates typically have a bigger effect on ride quality than spring rates do. So even if you're not swapping springs, revalving is still something to consider if you want a more compliant ride. If you make anything other than modest changes to the spring rates, you're going to need to have your dampers revalved to maintain that sweet balance between the damper and spring that the manufacturer worked so hard to achieve. The R&D is why you paid the big bucks for your suspension kit. So, if you change your spring rates, do yourself a favor and call the manufacturer to ask if your dampers need to be revalved to match the replacement springs.
Nothing Shocking
Many of us know dampers help smooth out bumps and keep our cars from porpoising down the highway like a herd of dolphins... but beyond that, most know little about how dampers really work... or how they actually improve performance and ride quality. Just what is it inside those magical tubes that can make our cars ride and drive so well under many different conditions?
To answer these questions, we took a trip to the TEIN USA headquarters to pick their brains about dampers. TEIN spends a great deal of time developing and fine-tuning its suspension kits. TEIN's R&D engineer, Katsuma Nakai, is a 10-year TEIN employee who previously worked for TEIN in Japan as an engineer. He's now in charge of developing and tuning new suspension systems for TEIN USA.
 |  Here's a TEIN twin-tube damper...  Here's a TEIN twin-tube damper that's been disassembled and is ready to be revalved. There are two basic types of automotive dampers: twin tube and mono tube. In the picture, you can see three major parts in the tray. The big green thing is the dampers external housing and threaded sleeve. The tube to the left of the external housing is the inner tube (hence the name twin-tube). The third part in the tray is the damper piston shaft assembly and is where the shims and piston are located and what will receive the most attention. |  As you can see, the oil in...  As you can see, the oil in dampers gets dirty just like the oil in an engine. Here's the fluid Nakai poured out of the old damper next to some fresh oil. One of the less-mentioned advantages of having a high-quality coilover setup is that they are rebuildable... something many lower-quality suspension setups cannot claim. |
 Once the damper's been opened...  Once the damper's been opened up, the next step is to disassemble the damper shaft/piston/shim assembly. Here's the bare shaft after all its parts have been removed. The parts that you see above the damper go inside the shaft and are what make the damper adjustable. After final assembly, a knob will be placed on the end of the shaft, allowing the user to adjust the damper. |  Once the damper is completely...  Once the damper is completely apart and cleaned, reassembly can begin. Here is the top of the shaft assembly where the piston and shims will be located. |  Here the same shaft after...  Here the same shaft after the new piston and shims have been installed. The piston is the big black donut with the small holes around the outside edge. The washer-looking thing on top of the piston is a shim. This assembly goes inside the internal-tube of the damper, which in turn goes into the main tube. Got it? |