Polyurethane bushes have become popular, as they noticeably stiffen the suspension and are claimed to outlast the OEM rubber equivalents. The same effects could be accommodated by using harder rubber compounds or by changing the tube diameters. However most users do not understand how torsion bushes are intended to work and how these alternatives differ in principle and the problems they create. The recent popularity of polyurethane after-market replacements has drowned out the advantages of the proven designs, resulting in stiction, binding, squeaking, harshness, and need for regular greasing.
Polyurethane is used in place of the rubber portion of the factory bushes. Unlike the rubber bushings, these bushes are not bonded to an inner and outer sleeve and are sometimes used simply because they are easier to fit. However, if easy to fit then there is no interference and hence a loss of stiffness will result. In typical automotive use, movement of the control arm will cause the internal surfaces of the sleeves and bush to slide to accommodate the shearing forces. This raises the issues of stiction and binding, both of which can affect steering predictability under extreme handling conditions.
