| Jeff Goji's Suspension Page - Shock Damping 101 |
| Alright ladies and gentlemen, I decided to share the shock absorber knowledge wealth and post up some shock dyno graphs for everyone's shock absorber education. I've also taken the liberty to write this somewhat brief explanation of how shock absorbers work, what the two different types of damping are, and a small explanation on what damping speeds are. The point of this thread is to help educate anyone looking for shock information or looking to find a dyno graph data which I'll supply as it becomes available to me. Shock absorber function: Shock absorbers, or more appropriately, Dampers, have the primary function of helping to control the energy stored up by the springs. A spring is a remarkable depository of energy. When the spring is compressed by a bump or a change in load on the spring, it stores the energy of the initial motion and feeds much of it back in the opposite direction. Without control, the spring would go through a number of cycles of compression and extending in response to it's first deflection, losing little energy with each cycle. If the springs were allowed to go uncontrolled (undamped) every time they encountered a bump or change in inertial loading, the car would be bouncing all over the place and be, for the most part, uncontrollable. Bump and Rebound damping: The shock absorber or "damper" has resistance to motion in two directions. It resist compression (making it shorter) and it resist extension (making it longer). When some force acts on the suspension system to compress the spring, it also compresses the shock. When the shock compresses, it's called "going on the bump." If the load is removed from the suspension, the spring gets longer and the shock extends - a state known as "going into rebound." Low-speed damping: Controls the springs through slower shock movements such as body roll movement or the speed of weight transfer. Too much low-speed damping will hurt overall grip, too little will make the car feel like a "boat at sea" and will be slower to react to driver inputs. High speed damping: Controls the spring under high speed movements such as when you hit a pothole or other sharp and abrupt bump. Too much high speed damping and the spring can't absorb the bump properly and you get a very rough ride and the tire can lose adhesion over multiple bumps such as on a rough road. Too little, and the spring energy isn't dissipated fast enough and the tire can lose adhesion over rough section of road or over an abrupt bump. Putting it all together: Low speed damping is the 0 - 2.5 IPS (inches per second) range and is where shock absorbers spend most of their life, unless you drive on bad (Houston) roads often. This is one of the reasons that Mazda commonly piles on loads of low-speed damping with their "sport package" options (99-Sport and Mazdaspeed Miatas). It gives the car a much "sportier" handling feel and makes the car feel like it's sporting stiffer springs than what it really has on it. Anything above 2.5 IPS is considered to be high speed damping, it's a sudden "spike" in shock speed when you run over a bump or hit a pothole. Everyone has an opinion on how much compression damping a vehicle needs... Some people believe that you let the springs do the actual work on the "bump" side and dial in just enough compression to adequately control your un-sprung weight. After all, if you have an actual spring, why do you need more compression than necessary to further dampen the un-sprung weight into almost a "death grip"? Well, this brings us to the second camp... This camp is like Mazda, they believe in using more compression damping then needed to control the un-sprung weight to give the vehicle a more sporting handling behavior and not have to fit stiffer springs. In theory this seems like a good idea, and in practice on dry, smooth as glass roads or on a smooth race track or autocross course, it can be applied with much success. The third camp, believes that rebound and compression are symmetrical and you need to increase one with the other to maintain a balance in all-out grip and handling, and maintain ride compliance. FatCat Motorsports tunes it's shocks along these lines, and it works. I've sampled suspensions from all three methods of damping as described above. I will flat out tell you that I'm a firm believer in the way FatCat Motorsports goes about tuning the damping as I've found that it just plain works and is the most effective method for bringing good ride quality and good handling into almost perfect harmony. The one thing every camp can agree on however, is damping on the rebound side. None of us want to over-damp a spring in rebound damping, as this leads to "jacking down" onto the bumpstops and will cause an overly harsh ride and even worse handling. Well actually... I say everyone, but in truth the Autocross community is one of the worst for running shock absorbers with entirely too much rebound damping (and often compression damping as well). You mostly see this in stock classes, where the rules prevent you from changing springs. Basically they crank up the shock absorbers as high as possible, giving up all-out grip in favor of transitional response and feel. The one time the average stock class autocross guru will go against this conventional wisdom of the herd is in the wet, where the higher grip of the more relaxed damper settings will payoff much better than the "death grip ultra responsive" over-damped settings. An example of this comes to mind back in 2007... Paul's MSM was on road race tires and stock MSM Bilstein shocks. The MSM Bilstein shocks have amazing amounts of low-speed damping, especially in the compression range, and are at home on a dry track. In the wet however, it was the slightly under-damped 2007 NC on less grippy street tires that I was better able to balance in the wet at the limit, and set times just as quick as the more powerful and higher damped MSM. Very surprising to me at the time given how absolutely horrible the NC felt to me in the dry. My personal opinion on shock absorber damping: I think it depends ENTIRELY on your use of the car and the condition of the roads, race track, or autocross course you are going to drive on. There just isn't one damper setting that will work for EVERY condition out there; this is the reason we are seeing more and more "magnetic ride selection" options being made available for various sports cars from various manufacturers all over the world. It's the reason the GT-R, Corvette ZR1, and Porsche 911 Turbo just to name 3 examples have multiple shock absorber damping profiles to fit varying conditions. The super soft under-damped shock absorbers found on the 06-08 NC sport models will not be optimal for autocross or track driving, and may not even be suitable for someone seeking a truly sporty handling vehicle. And the inverse is also true in that a autocross or track driving setup will not be optimal for the 06-08 NC owner seeking a comfortable cruising car. What's best for absolute grip in the dry on 225/50/15 R-comp tires on a smooth as glass autocross course will never work properly on the same car sporting 195/50/15 street tires on a bumpy road in the rain. Shock absorber damping is like anything in life, it's a compromise. The trick is figuring out the priorities, and spending your money accordingly knowing full well the pay-offs and compromises involved in your decision. - Jeff Goji. |