Variable spring rate chassis

Prior art handles come with matching hardware. Changing handles can mean the need for a change in hardware so that the spring bias is suitable for the weight of the handle or lever. Provided herein is a interchangeable handle set comprising interchangeable handle set having a housing; a spindle rotatably mounted to the housing; a spring collar rotatably mounted to the housing; an installed handle comprising either a first handle or a second handle, each configured to be rotationally coupled with the spindle and each including a manually graspable portion and a shank extending from the manually graspable portion, wherein the second handle includes an engagement feature and the first handle includes a disengagement feature, wherein the engagement feature and the disengagement feature is defined by the shank of the respective first and second handles, wherein the engagement feature is configured to rotationally couple the second handle with the spring collar, and wherein the disengagement feature is configured to permit the first handle to rotate relative to the spring collar. This provides selective coupling of the spring collar to one type of handle, for example a heavy lever, and selective decoupling of another type of handle, for example a lighter knob.