There can be huge advantages to using a spring Pre-Loader on your race car. It is most commonly used on the right rear and allows you to run a soft spring but pre-load it so it has a high static load. You will get the benefits of running a heavy spring to get you into and through the center of the corner but also have the benefit of a lighter spring for more traction coming off the corner. For example, if you have a 500lb spring in the right rear of your car and it has 500lbs of weight on it, it should be compressed 1". If it travels another inch it will have 1000lbs on it. Now if you use a JOES Spring pre-loader and compress a 125lb spring 4 inches it will have 500lbs on it. If it travels another inch it now has 625lb on it, 375lbs less than a 500lb spring. Fits all major shock brands and 10”-12" springs.