When starting modding and even if you have some experience in modding, here is perhaps something useful I stumbled upon, some reference values and information to help to understand why everything is as it is:
Anything relatively modern seem to be quite low, for racing purposes 2-2.5Hz is good aim, anything around 3Hz or more of wheel rate must have downforce or load added, I believe, to get Hz you can use this tool, just remember that motion ratio and difference in wheel rate and spring rate, adjust numbers you input accordingly.
Edit 25.1.2012 6:50AM:
Attached latest version of my calculator spreadsheet, all formulas are now verified and working, added also new stuff to damper calculation as I finally came accross to info I remembered seeing years ago, but only until now managed to find anything about it.
That was Rebound to Bump damping ratio, so I made three values for that to make it easier to pick appropriate bump damping for calculated rebound damping, also added some explanation of that to orange area.
That calculation should now help a bit more to get dampers in range, but as always drive and test car well, try to find measured data from dampers, but from my experience that is really hard, during 5 years I have came accross only Miata damper results and some generic data, but nothing really useful apart from that.
Damper calculations should be verified with real world data, might try Miata stuff some day and see if I can get them converted to rF units and find all the data from those cars to make comparision of real data and what my calculator gives, but for me calculator produced values seem to work quite well, feedback however is always welcome.
According to this site:
Frequency for road car is 1.33 - 1.67Hz (CPM to HZ = CPM / 60) and from presentation you can see how modern cars have 1.1-1.3Hz at front, of course modern cars are hardly a 1000kg weighting either. For 1000kg race car they suggest max of 2.17Hz.
For example Corvette C6 HDV has front spring at 22500 and in comments there is mention of 1.3Hz rate and that is a sports car.
ISI ZR has frequency of 2.11Hz at front, that is in HDV, so it is full grown race car with only looks of steet car at base A tune, any upgrades will make frequezy just higher, getting weight reduced will make frequency higher so that is partly why it has that feel of go-kart instead of a car.
Many mods have been using values close of 100 000 or even higher resulting suspension that is close to iron bars instead of springs as modders have not had information how things are in reality.
Often modding is guesswork when there is no data available and result is more or less questimate, but with this information it can be closer questimate. Of course better if one has the data.
Using real world spring values is making sense only when motion ratio is known, if not known, then set wheel rates and get frequency to proper range, even better if one can get it measured from real car. AdjustSuspRates= is setting to adjust depending from if one likes to set wheel rates or spring rates + motion ratio.
To get those US spring units into rFactor units you can use this, multiply by 1000 is required though to get right unit to HDV as I believe in HDV unit is N/m and to convert mm to m (meter) you need to multiply by 1000:
That should give some insight of how to make car act like a car instead of go-kart, inertia and cg height (link to get idea what is range where those should be
) plays part in that too as well as dampers (Need to be enough soft to allow easy body movement and after braking typically one bounce, but remember firm ride is often made with dampers, not just by stiffening springs, one need to adjust according to vehicle), so it is always sum of many, but by reading and understanding presentation chance of success is multiplied by many times
Same applies to rF2 also, there might be of course some different parameters to play with, but frequency is still same stuff and same goes to any sim in that matter.
Hopefully this is some help for someone in a future.
edit: Here are few links that contain real world skidpad results of various kind of cars. Please, do note that peak G forces what you see at Motec when driving around the track can be higher, skidpad results are often constant G force when driving at steady maximum possible speed while still keeping same line on 200ft or 400ft circle, you need such test track which preferrably has real world road parameters, means that track friction should not be too optimistic. I have been told that 1.0 would be too high for such, but then again I don't know much about track making.
Anyway here are the results that might give some insight of what to except from street cars, there are also some sport cars and I think one can be considered as race car:
Here is bit insight to old vs new american muscle for those interested, 1969 Z28 getting 0.8G:
Anyway those should give at least some direction to what kind of numbers can be excepted, tires of course are big part, but suspension and Center of gravity (CG height, CG rear) are big part in there as are springs and dampers too.
When building a car, if nothing else, one should try to get into correct range of performance and cornering as that is what gives players immersion of driving that actual car and not just car that looks like that actual car, when you get skidpad results, acceleration, braking, top speed, inertias, cg height and suspension frequency close, it is almost certain win already in my books at least.
Okay, let's put up some information here about springs.
Let's say you have pulled of coil spring out from your car and try to figure out how on earth I get this into rFactor.
No worries, Mid-West Spring and stamping to the rescue!
I think that is the most accurate spring calculator, I have tried lot of those online calculators, but those don't seem to quite cut it, often I end up way too high rates, but this tool seem to get it much closer.
Good thing is that it is very light and fast.
Measure spring, input units, in case you live in metric world, you need to convert measured units to imperial ones first, active coils is usually total coils -2.
Choose compression spring and if your spring ends are cut so that top of spring is flat, then use ground button, if ends are not cut then the button on left of ground button, after than push calculate.
At lower section next to Buckling ratio is button with letter M push that and you see Newtons at Rate box, rememember to multiply that by 1000 to get right units for HDV.
You might be lucky and find spring data from internet too and you can use this tool to calculate them to proper units.
Just remember that often there is motion ratio of something else than 1 and that must be put into springmult= but mostly all McPherson setups are 1. Alternative is to work with wheel rates, then this tool is not so useful.
Motion ratio or wheel rate are both very difficult to come by however, easier to find such vehicle from junkyard perhaps and measure there or if doing your own car it can be measured from the car. Google measuring motion ratio will give lot of help with this one.