spring rates

[johntolson510]

Hey every one I'm thinking of getting a pair of coilovers from t3 and they want to know what spring rate I Whould like so my question is dose anyone know what the mean and what Whould be a good spring rate for use as a day lie driver and for mountain runs

[john510]

Assuming its a 510 and for the front a 200 lb. spring is plenty.

[datzenmike]

Spring rate very simply is how many pounds needed to compress the spring one inch. Hold that thought.

 

The springs are what the car rides on so it's integral with handling performance and comfort. Stiffer spring rates limit suspension travel and for the most part affect handling in a positive way while affecting ride comfort in a somewhat negative way. You may have to give up some comfort to get the handling where you like it. No one can tell you what that is, you would have to find out by experiment or by driving a similar car with a known spring rate and see if you like it.

 

The stock 510 front spring rate is about 89 pounds each. Serious racers run 300 lb/in springs and more. Remember that there are extreme pressure exerted on the chassis and the springs when racing around a track at over a hundred MPH that are not felt on the street at fifty. Three hundred pound springs may not be for everyone on a street car. I have a 710 wagon and run a 150 lb/in front spring and enjoy the ride and handling increase from the stock 100. After some traveling and getting used to it I'm of the opinion that increasing to 175 might be even better and perhaps in the future I will do so, but I realize that at some point it will go the other way and be hard to live with. I would estimate that a 200 lb/in would be an average spring rate perhaps to start with and go up or down from there. I know.... others will say start higher but I can't say what you will feel is right.

 

Now the rears. They should roughly follow the fronts for rate. Too much front spring stiffness or too much soft rear spring will increase understeer and adversely affect the cars neutral handling*. The 510 rear springs are located not above the wheel center line but forward slightly on the control arm. Effectively there is a mechanical advantage placed on the spring by this arrangement of about 2.8. Think of a pair of pliers where the spring is moved towards the hinge point and away from your hand. It becomes easier to compress so the spring rate has to be increased to get the same effect at the wheel. If the rear spring rate (at the wheel) is to be about 90 pounds per inch, to match the fronts, then the actual spring rate will be 90 X 3.8 = 338lb/in.  Yes, race cars run 1,200 and 1,300 lb/in springs!!!

 

Take note that if converting the 510 rear springs to coil overs they will be almost over the wheel center line and the 3.8 times does not apply.  

 

 

Too much front spring stiffness or too much soft rear spring will increase understeer and adversely affect the cars neutral handling*. Keep in mind that increasing the front spring without increasing the rears will affect how the car handles by adding understeer. This is the tendency of the car to plough straight ahead when turning a corner instead of turning. Any spring change should be viewed as affecting the whole cars handling so look at probably increasing the rear springs as well.

 

 

Spring rate can also be calculated fairly easily for those who would like to trim a part coil off their springs to increase the rate. Keep in mind it's one way, stiffer, and can't be reversed. (this will likely lower the ride height) Also an unknown spring or a known spring rate can be checked by a few easy measurements and calculations. It only looks like rocket science.

 

Never ever heat a spring to lower a car. Just putting that out there.

[Dime Dave]

Mike,

I have always used 3.8 x wheel rate for calculating the spring rate of stock position 510 rear springs . If you are looking for a 200# wheel rate you would need a 760# spring in stock position. (200# x 3.8).

 

As you noted, the stock front springs are 89#. Stock rear spring rate is 357#. Using 3.8 as the rear wheel rate factor, the 357# rear spring yields a 94# wheel rate (357# / 3.8) basically the balanced front to rear wheel rate that everyone recommends when changing out springs.

[datzenmike]

Thanks Dave. Yup I totally got it wrong. Corrected. Over 300 sounds much better.

[KlassicMotion]

Here is some info:

 

http://community.ratsun.net/topic/59228-understanding-spring-rate/