In order to enable the appropriate amount of understeer to be produced in a suspension wherein the rear wheel is steered to produce a toe-in effect by a lateral rod/knuckle arm arrangement, a device which in some embodiments is hydraulically controlled and in others is mechanical, permits distortion of the elastomeric bushes which form part of the suspension unit to produce a relatively large amount of understeer at high speeds and restricts the distortion at lower speeds to reduce the amount of understeer to a level suitable for that speed.