Awhile back Lee asked me to post some of the stuff that I have found out about spring selections. Here are a couple of links that I use to figure out what my wheel rates for the BMod car are. Now, understand that wheel rates are not necessarly the same as spring rates. Wheel rates are the effective rate of the spring as measured from the wheel. This takes into account the leverage advantage that your suspension has on the spring.
Typical MacPherson strut type suspension has a leverage ratio of 1.1 to 1. Other types of suspension you will need to calculate the leverage ratio. At the Strawberry Hill Cobra website ( http://eaglewoman.rscsites.org/cobra/index.htm ), click the link "Tweaks", then select "Measuring the Motion Ratio". They give a very good description of how to measure and then calculate your Motion Ratio.
Once you have calculated your Motion Ratio's (front and rear) then you can go to:
There are a few things that you'll need to know before you can calculate your wheel rate.
1) Corner weight
2) Unsprung weight
3) Spring rate
Once you have those values you can plug them into the calculator.
In box number 2) Suspension Leverage, select "I know this value" and enter the leverage ratio that you calculated earlier.
Once you have entered this information it will calculate your:
1) Efective Coil Rate
2) Wheel Rate
3) Static Deflection
4) Wheel Frequency
5) Natural Frequency
Below the results is a general guideline on types of cars and Wheel frequencies.
From the Competition Car Suspension book.
60 - 80 cpm Comfortable road car.
80 - 100 cpm Sports road car.
100 - 125 cpm Racing cars without wings or ground effects.
200 - 350 cpm Current racing cars with downforce.
- 500 cpm Ground effect era cars.
Another note to keep in mind when selecting springs is to keep the front to natural frequency about 10% higher towards the front.
Hope this is helpfull!