Editor's note- Springs are one of the most important (and noticeable) parts of a car's suspension to consider when preparing it for track use. Choosing spring rates in the most effective ballpark rates for your application and desired use can be tough, but the following is a good way to spend a little time calculating what might be the best "optimal" choice for you. Over the past 2 years, I've personally gone down in spring rates a great deal from what I initially ran on my racecar, and gained nothing but grip, speed, and confidence in the car. We hope you find this article interesting and informative! -Adam
By Promo Ravi
Stop Over Springing Your Car
I’ve been driving and instructing for nearly a decade now. Over-springing suspension is a common issue I’ve seen most drivers make, from novice drivers to semi-professional drivers alike. What I mean by that is they add too much spring (too high a rate of spring).
What is spring rate? It’s the suspension coil that dictates how much your strut/shock travels during suspension load. The "strength" of the spring as it is compressed. Why does this matter? If you have too little rate, you have excessive body roll. If you have too much rate, you’re potentially losing out on a lot of possible grip due to bouncing, shocking the tires to hard in transition, etc. How do you correct this? ...This part will take quite a while to explain.
Let’s start with your ride frequency. Your ride frequency is…well..... Let me allow Optimum G to explain this better than I ever can.
Let’s take a look at the ride frequency examples provided. The higher the ride frequency, the more “Racecar” the suspension is, to an extent. How do you calculate what spring is most optimal for your car?
Follow this link for a great spring rate calculator. - http://www.usrallyteam.com/content/tech/suspension_calculator.xls
We’ll use my EVO as an example. It has a DHP rear wing, 80” front splitter, and 12/14kgs spring rates.
The ride frequency of my car is 2.52 in the front, and 2.69 in the rear. It’s rated as a “High downforce racecar”. However, you need to take this with a grain of salt because my car is not a racecar as it barely runs. (And for a long time no one believed it existed - Austin) What do you need to pay attention to? What your ride frequency is and how you can determine what it is.
If the motion ratio of your suspension (the amount of shock travel for a given amount of wheel travel) can change your ride frequency, the slack and movement your bushings provide can also alter how well your springs are doing their job. Are you over sprung to make up for the fact your suspension allows for a lot of slack? Are you under sprung, and allowing the car to roll excessively? After you’ve calculated what your optimal ride frequency, how are you going to apply it to your car?
For this off season, take your time and build your suspension using all of the information available to you. Use the internet, Google is amazing. If your buddy suggests running 18/18k’s on your stock S2000, maybe ask him/her why those numbers were magically plucked from the air. Why do you need that much spring? How does it help you? Are you using spring rate to fix an issue, or are you using spring rate to assist your driving?