Hendricksonโs Progressive Load Spring for its Haulmaax vocational rear suspension system is an elastomeric spring that works with the rubber bolster springs in the companyโs Vari-Rate Spring system to facilitate improved ride quality in both loaded and unloaded conditions. The PLS is engaged continuously to help improve unloaded ride performance, and as payload increases, the spring further engages and functions together with the bolster springs to help provide additional stability. The load springโs constant engagement also helps eliminate the need for shim adjustments for most applications.