Ever wonder why you see some companies listing their spring rates in kilograms (kg) and some in pounds (lb)? Well the short of it is that most companies headquartered in the United States will still use the Imperial system of measurement (pounds, lb), while those headquartered throughout Europe and Asia will use the Metric system of measurement (kilograms, kg).
When it comes to spring rates it is customary to measure how soft or stiff a spring is by how many units of force or weight, pounds or kilograms, it takes to compress the spring within a given distance increment, typically inches and millimeters. While companies using the Metric system will often list their spring rates with either k or kg, it really should be listed as kg/mm (kilogram per millimeter). So if a spring is listed at 5k it would mean it takes 5 kilograms of force to compress the spring 1 millimeter. If your spring rate is 450lb/in (pounds per inch) it will mean it takes 450 pounds of force to compress the spring 1 inch.
To test the spring rate, the spring is placed into a spring rate tester, like shown above, and is pre-compressed one inch (or millimeters if you’re using that measurement) and then compressed further to get the measurement for the next inch of compression. This will then tell you what the spring rate will be for that inch. You can then take another inch measurement if your machine will allow. Depending on the type of spring, this first measured inch will be sufficient but there are specific types that may require getting more than one inch of measurement.
Now unfortunately without having a spring rate testing machine of some sort, there really isn’t a way to home test a spring for its spring rate. Sometimes you can get lucky and the spring will have the spring rate printed on one of the coils. Often times this will be written like ‘400#’ or ‘#400’ letting you know the spring is 400lb/in. In most cases it will be best to call the manufacturer or supplier of the spring to confirm spring rate if it is not known.
Check back with us as we’ll be having more posts about springs, shocks, and other technical areas in future posts. Have suggestions on what you’d like to see explained in the future? Comment below and we can address those suggestions in future posts. Have any questions regarding springs or spring rates? Feel free to give us a call, 801-365-1440, or shoot us an email, [email protected].