P.S. i just wanted to add a brief overview of how damping and springs work, as i couldnt easily implement it above...
a damper (very) basically consists of a cylinder filled with oil with a hole in the top that a shift can move in and out through. on the end of the shaft is a piston which seals to the sides of the cylinder, but contains some form of bleed mechanism which allows oil to pass through in controlled amounts. the system is varied depending on the direction the piston moves in, which gives you your bump and rebound valving. something il say here which isnt really related, but which most people understand wrongly is that "gas" dampers (aka gas filled struts, emulsified dampers (gas mixed with the oil, some dampers have gas in a seperate chamber),etc) still contain oil. ALL dampers have oil in them, and dampers without gas when compressed will stay compressed, they dont pop back out. the gas inside dampers will cause them to push the rod back out, but this is at such a tiny force it had no effect on the car. the gas pressurises the inside of the damper so that it can allow for expansion of the oil under heat and allow for fast movement of the oil and prevent/reduce cavitation in the oil
so youve got bump damping and rebound damping. the sole purpose of the damper is to control the SPRING, it is the job of the spring to control the ride of the car
so the spring is compressed, it pushes the damper down and the dampers bump characteristics control the rates at which the spring can be compressed. all the damper really does is offer up an opposing force to the spring. the car pushes the spring and damper together and inside the damper the piston being forced through oil offers up resistance, which manifests itself as an upward force opposing the movement of the car and spring. stiff bump damping leads to a slower rate of compression. the way it works is quite simple, its the fine details in what sort of rates of compression you want which is where it gets complex lol
rebound is the opposite of bump, this is the force which resists the damper expanding again. as said above about gas dampers, the damper itself doesnt possess enough force to push the cars weight back up, they dont generally possess enough force to overcome a human pushing the rod in, depending on the gas pressures used. if there wasnt a spring on the car, the damper would expand back out. in rebound, the spring is trying to expand (as it naturally does) and in order for it to do this it has to pull the rod back out of the damper. the damper offers a force to resist this. stiffer rebound causes the spring to expand more slowly, again, its a fairly simple concept.
now to consider dampers with relation to spring rate. if you have a soft spring then the cars loads will compress it more easily. thus you ideally need stiffer bump damping to stop the spring from compressing really quickly and unsettling the car and causing excessive initial body roll. the rebound however can be softer because there is less force from the spring trying to expand the damper. since the damper is only there to control the spring, and the spring is pulling on it less hard, it makes sense that less rebound is required (generally, im stating this in very basic terms here, things are rather more complex in real life, but the basic principles still apply on the most part)
stiffer springs on the other hand compress less, and are less willing to compress, so bump damping can be softer. rebound on the other hands needs to be much stiffer, its basically the opposite of the above
now here are the 2 issues....
1. damping is there to control the springs, but the rate at which the wheels move is the key to a car gripping and handling well. so if you are needing to crank rebound up to cope with a stiff spring, you are also going to sacrifice traction on driven wheels for example. cars are dynamic objects, everything affects everything else
2. most people dont change dampers, the first thing they opt to change is springs (usually for lowered items). jap cars come with tons of rebound from the factory, japanese roads are really smooth, and japanese manufacturers like their cars to be pointy and feel like go karts, it sells well to people who dont really know how to truly drive the car. and this excessive rebound means that the car lends itself well to stiffer springs, as the dampers control the spring just fine in rebound and so people think this is what is best. the problem is that the bump damping is then far too soft for the stiff spring and the balance isnt there. it usually feels good, but it isnt fast. how many times have you seen scoobies and evos getting destroyed on track days by mk1 golf, 106 gti's, clio 172's, etc which are 200bhp down on them, but just destroy them around corners? most scoobies and evos are on cheap import dampers that are overly stiff on rebound, and are then stuck on stupidly stiff springs. the fastest track evo's run about 1-200lbs softer on spring rate than the average track day car, and their damping curves are basically turned upside down lol
thats not a particularly comprehensive guide on the basics of damping, its just a brief overview so that some of the above will make more sense. damping force changes dependant on speed, and its the fine tuning of low speed, mid range and high speed damping that determines how well a car sticks to the road, and the feedback and confidence that it gives the driver. but hopefully it gives enough insight to get people thinking :)
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Originally Posted by Jim-SR
