referring to fig1 a wheel suspension 10 includes a wheel 11 which rotates on an axle 12 . axle 12 passes through a pair of aligned and opposing openings 19 in a pair of spaced planar and generally parallel side walls 14 . bearings 13 are mounted within a central axial opening 21 of wheel 11 and are adjacent the outer surface of axle 12 . a resilient connection 22 between the ends of axle 12 and side walls 14 includes a pair of inner cover plates 15 having a disk shape with a central opening and attached to the outside of side walls 14 around openings 19 . the connection can be made by such means as welding or fitting . inner cover plates 15 each have protruding annular bosses 18 for sitting in openings 19 of side walls 14 . resilient connection 22 further includes a pair of elastomer members 17 having a generally disk shape with a central axial opening for passing axle 12 and bonded to the outer surface of inner cover plate 15 . a pair of outer cover plates 16 have a disk shape similar to inner cover plate 15 with an axial opening defining an inner diameter . however , the inner diameter of outer cover plate 16 is smaller than the inner diameter of inner cover plate 15 so that radial movement of axle 12 causes interference , first between outer cover plates 16 and axle 12 and then interference between axle 12 and inner cover plates 15 . elastomeric members 17 are bonded to both the adjacent surfaces of inner and outer cover plates 15 and 16 so that movement of outer cover plates 16 is damped or resisted in that a shear force is applied to elastomeric members 17 . nuts 20 are attached to the outer ends of axle 12 and abut the outer surfaces of outer cover plates 16 . advantageously , at least one of the nuts has internal threads mating with external threads on axle 12 so that nuts 20 can be tightened toward each other and apply a compressive force on elastomeric members 17 . such compressive force can be used to reinforce the bonding force between elastomeric members 17 and cover plates 15 and 16 of wheel suspension 10 . the assembly of wheel suspension 10 typically includes forming generally circular openings 19 in side walls 14 and attaching side walls 14 to the cart or truck which is to be supported . elastomeric members 17 are bonded between inner cover plates 115 and outer cover plates 16 . the inner sides of inner cover plates 15 are attached to the outer faces of side walls 14 adjacent openings 19 . wheel 11 is positioned between side walls 14 and axle 12 is threaded through openings 19 and central opening 21 of wheel 11 . attaching nut 20 to the ends of axle 12 prevents axle 12 from slipping out and provides for compression of elastomeric members 17 . in operation , wheel suspension 10 provides a linear suspension or damping force when deflection of wheel 11 causes deflection of axle 12 . that is , the travel of axle 12 is radially limited by the radially most inward portion of inner cover plates 15 and side walls 14 around openings 19 . that is , elastomeric members 17 continue to increasingly deflect until axle 12 hits against the limit of travel which , as illustrated in fig1 is the innermost boundary of inner cover plates 15 . further movement of axle 12 causes corresponding movement of side walls 14 and , indeed , of the truck or cart which is supported . the force for damping or suspension provided by elastomeric member 17 as they are deflected or sheared from a rest position to a maximum displacement is linear with respect to the displacement of axle 12 . referring to fig2 a nonlinear suspension or damping force can be obtained from a wheel suspension 50 wherein like numbered components are similar to the components of wheel suspension 10 . bearings 13 &# 39 ; are attached to the interior of wheel 11 &# 39 ; and against the outside surface of axle 12 &# 39 ;. openings 19 &# 39 ; and side walls 14 &# 39 ; pass the ends of axle 12 &# 39 ; to nuts 20 &# 39 ; which are at the end of axle 12 &# 39 ;. however , in contrast to wheel suspension 10 , a resilient connection 51 includes three pairs of elastomeric members 60 , 61 and 62 and four pairs of cover plates 55 , 56 , 57 and 58 which all have a central axial opening defining an inner diameter . inner cover plates 55 each have protruding annular bosses 65 for sitting in openings 19 &# 39 ; of side walls 14 &# 39 ;. the pair of cover plates 55 is adjacent the exterior of side walls 14 &# 39 ; around openings 19 &# 39 ;. continuing successively outward from cover plates 55 , there is a pair of elastomeric members 60 , a pair of cover plates 56 , a pair of elastomeric members 61 , a pair of cover plates 57 , a pair of elastomeric members 62 and a pair of cover plates 58 . nuts 20 &# 39 ; abut the outermost extremity of resilient connection 51 and can be tightened to apply compressive force to resilient connection 51 . elastomeric members 60 , 61 and 62 are each bonded to the adjacent cover plates 55 through 58 so that deflection of cover plates 55 through 58 causes a shear force to be applied to elastomeric members 60 , 61 and 62 . both the elastomeric members and the cover plates have decreasing diameters as resilient connection 51 extends outwardly from side walls 14 &# 39 ; to the connection with axle 12 . the inner diameter of outermost cover plates 58 is substantially equal to the outer diameter of axle 12 &# 39 ; and responds immediately to movement of axle 12 &# 39 ;. the deflection created by such movement is applied to the adjacent elastomeric members 62 . when axle 12 &# 39 ; has deflected sufficiently to engage the larger inner diameter of the next innermost cover plates 57 then cover plates 57 also moves with further movement of axle 12 . as a result , there is no further increase in the applied shear force to elastomeric members 62 but there is an increase in the applied shear force in the elastomeric members 61 , inward of cover plates 57 . similarly , when deflection of axle 12 &# 39 ; is such that the outer surface of axle 12 &# 39 ; strikes the inner diameter of cover plates 56 , there is no further increase in the shear force applied to pairs of elastomeric members 61 and 62 but there is additional shear force applied to elastomeric members 60 . finally , when the outer surface of axle 12 &# 39 ; reaches the innermost diameter of cover plates 55 no further increase in the shear force is applied to elastomeric members 60 , 61 and 62 and no further deflection of axle 12 &# 39 ; may be realized . the above described sequence in the increase in stiffness introduced successively by stopping elastomeric members 60 , 61 and 62 from further deformation provides a nonlinear suspension system . that is , when the two cover plates adjacent an elastomeric member both contact axle 12 &# 39 ; there is no further deformation of the elastomeric member between the cover plates and wheel suspension 50 has an increased stiffness . such a suspension system is particularly advantageous because there can be effective damping of a relatively broad range of travel of axle 12 &# 39 ; without it being necessary to have particularly high damping at the beginning of travel of axle 12 &# 39 ;. instead , there can be a substantial increase in the damping force as axle 12 approaches the end of its travel . advantageously , cover plates 55 through 58 are made of a metal which is nonresilient and is easily attached to both side walls 14 &# 39 ; and elastomeric members 60 , 61 and 62 . elastomeric members 60 through 62 are sufficiently resilient that the opposing major faces of each member can be displaced with respect to each other by distances equal to the differences between the radii of the central axial openings of adjacent cover plates . the material of the elastomeric member is chosen so that for this displacement there is a desired shear force resistance . the size and number of layers of elastomer will be determined for each application according to the payload range and the desired dynamic characteristics of the system which includes the caster and the payload . the amount of shear stiffness supplied by elastomeric members 60 , 61 and 62 is also dependent upon the radial extent of each of the members . as shown in fig2 the outer diameters of elastomeric members 60 through 62 are also decreased in accordance with the decreasing inner diameter of the elastomeric members 60 through 62 . similarly , the outer diameter of cover plates 55 through 58 decrease . it should be recognized that the damping force provided by resilient connection 51 can be varied by varying the outer diameter of the elastomeric members and cover plates . further , the inner and outer diameters of each the cover plates and each of the elastomeric members need not be constant with axial distance along axle 12 &# 39 ; or 12 . for example , the outer diameter of the elastomeric members may vary so that there is a smooth connection between the outer diameters of adjacent cover plates . the elastomer members in accordance with this invention do not rotate and as such are not subject to varying deflection as a function of the speed of rotation . such deflection causes heat loss due to such reasons as hysterisis which results in energy being dissipated without performing useful suspension work or forward travel . the nonrotating elastomeric rings are flexed only when a load is applied to the wheel and that there is no deflection as a result of wheel rotation alone . further , the relative position of the elastomeric members with respect to the wheel suspension is advantageous in that there is sufficient room radially outward and axially outward for a variety of elastomeric configurations . various modifications and variations will no doubt occur to those skilled in the various art to which this invention pertains . for example , the resilient connection may extend inward from the side walls to connection with the axle instead of , as shown , extending outwardly . these and all other variations which basically rely on the teachings through which this disclosure has advanced the art are properly considered within the scope of this invention .