This App is a very simplified calculattion methode for estimating the rubber bearing basic stiffness (+/- 1mm) in depend from Shore (Shore hardness range: 30-90) and geometry. This calculation only applies to natural rubber.
Attention: Calculated values are only reference values! No warranty, guarantee or liability is accepted!

For a correct calculation of the circular and rectangular shape, the ratio between the pressing area (Pi/4*D^2 - red color in the sketch) / free area (Pi*D*h - black color in the sketch) must be < 2,5.
For bushing shape too, the ratio between rubber thickness (D-d)/2 and height h must be < 5. If the geometry ratio is not correct, a warning appears with a request to change the geometries. For bushing shape - outer surface (Pi/4*D^2) is fixed and red surface (core) is movable.

Calculated stiffnesses can differ in reality. Accuracy problem arises from unknown material values. Poisson's ratio of rubber can vary between 0.45 and 0.49995 (some FEM program use 0.475 as default value), so the bulk modulus and tension-compression stiffness can vary greatly. The correct values can be determined in the material laboratory.

The influences of radii, overflows, temperature and preloads were not taken into account here. Therefore it is recommended to check the final design of the rubber bearing with the FEM program.