IMO bardzo ciekawy artykuł, który świetnie tłumaczy np. sensowność montażu twardszych sprężyn z tyłu w niektórych autach z lekkim tyłem.
This thread is really for people that are thinking of taking suspension tuning past buying some shiny parts and just bolting them on part of our hobby. What I hope to cover here is some basic tuning thoughts on how springs work with our suspensions and how to pick them to help you reach your handling goals.
First, just picking spring rates buy weight of the car does not work well with our cars. The reason for this is in the differences in the design between the front and rear suspensions. The best term to describe this difference is motion ratio, that is how much the shock/spring combo moves for every unit the wheel moves.
Here are the motion ratios(MR) for our cars..
Front MR = .909
Rear MR = .588
What this means is if the front wheel hits a 1 inch bump, the shock/spring combo moves .909 inch's upward and if the rear wheel hits a 1 inch bump its shock/spring combo moves upward .588 inch's. Well, since there is such a difference between the front and rear MR's , the rear of our cars need stiffer spring/shocks than the front even though there is more weight over the front wheels than the rear.
OK, now that you understand MR(I hope), lets get into how to pick your spring rates for the type of driving we hope to do. To do this we need to use "car math" to put the MR together with the sprung weight and a spring rate to get the suspension frequency.
The fist thing you need to do is find the wheel rate(WR), here is the formula...
WR = (spring rate) ( MR^2)
Here is a example for a 375lb spring on the front...
WR = (375)(.909^2) = 309.75
Here is a example for using a 600lb spring in the rear wheel..
WR = (600)(.588^2) = 207.6
Next you need to find the Suspension Frequency(SF), here is the formula.....
SF = (187.8)(SQRT(WR/SPRUNG WEIGHT))
You are going to need the "sprung weight" for this formula. The best number I have found is....
Front sprung weight=740lbs
Rear sprung weight=460 lbs
......note, sprung weight = the weight of that corner of the car less the weight of the suspension on that corner(suspension parts/wheels=unsprung wt).
Lets try this for that front number with the 375lb spring.....
SF = (187.8)(SQRT(309.75/740)) = 121.5
Here is the formula for the 600lb spring on the rear.....
SF = (187.8)(SQRT(207.6/460)) = 126.1
Now you have to convert the SF to Hertz(Hz). Here is the formula for that....
Hz=SF/60
Here is the final numbers for the front and rear suspensions
Front
Hz = 121.5/60 = 2.025Hz
Rear
Hz = 126.1/60 = 2.10HZ
So, what the heck does that mean? Well now you have a numbers that mean somthing....what do they mean? The stock springs are 249lbs ft and 440lb r, that comes out to 1.65Hz ft and 1.80Hz rear. If you like the way the stock car works but you are going to tires with more grip, you want to keep the difference of .15Hz, If you want more rotation, you might want to up the difference between the ft and rear to .2 Hz....Now, If you are going to go hard core autoX with R-compound tires, look to get 2.5Hz in the rear and 2.3 Hz in the front(thats 525lb+ft and 850lb+ rear). If you don't like bleeding from your kidneys or you are not running total gum ball tires, you might want to keep things between 1.8Hz and 2.1Hz.....
Ok, here is a brake down for what the spring rates mean in suspension frequancy.....
Front(lbs)/(Hz)...........Rear (lbs)/(Hz)
Stock...249/1.65.................................440/1.80
...........375/2.03..................................480/1.88
...........440/2.19..................................500/1.92
...........500/2.34..................................550/2.01
...........550/2.45..................................600/2.10
...........600/2.56..................................650/2.19
...........650/2.66..................................700/2.27
...........700/2.72..................................750/2.35
.................................................. .........800/2.43
.................................................. .........850/2.56
.................................................. .........900/2.58
.................................................. .........950/2.65
.................................................. ........1000/2.71
Ok, you should get the idea. I only posted the spring rates that Ground Control sells in the 2.25x6inch sizes.....But there are other spring dealers like Hyper Coil out there......
Another note, I have listed these spring rates in pounds/in, If you want to change over to Kg, just devide the lbs by 56....
example.....700lb = 700/56 = 12.5K
W wolnym czasie zmienie jednostki na metryczne.