Primary Spring
Springs are color coded in order to tell them apart and to identify their rate. (see chart A) For example, SLP sells a spring that is solid red, but has a gold and black stripe up the side and is rated at a 55/225. The color in most cases is given a rate which is essentially a measurement in pounds per square inch (PSI). In the case of the red/gold/black, the red doesn't have a psi rating but the gold and black do, the gold representing the 55 and the black representing the 225. Each psi rating is an actual measurement of how many pounds you would see on a scale if you were to compress the spring down to a specific height. The first number, called the preload number or, as some call it, the initial rate, is measured on the scale with the spring compressed down until it measures 2.25 inches tall. At this point the scale should read around 55 lbs. The second number or final rate would be measured at 1.25 inches tall with the scale showing 225 lbs. of pressure.
Now keep in mind that not all manufacturers use the same measuring points so if you want to compare springs from two different spring manufacturers you will need to find out how they measure their spring rates. Most spring manufacturers print the measuring point on the spring chart. An example of this can be seen under the clutching section of the SLP website (www.startinglineproducts.com).
