(Where is the Physics prefix? ;-) ) Just want to add this here as well since it applies to 5.3 as well: Case 747895 https://fogbugz.unity3d.com/default.asp?747895_gmsqj94tlfnrf6q3 Basically, wheel colliders will not roll unless they have motortorque applied. So, having a cart (without motor) and attempting to push it will not work with the current wheel collider implementation. Same thing goes for attaching a trailer to a car. The trailer will not roll even though the car is attempting to pull it with a large force. Only after applying motortorque (can be a very small value, say 0.1) will the wheels "wake up" and behave properly. This has been verified by QA, apparently bounced with the physics team (who considers it a feature). I have logged it as a feature request as well. https://feedback.unity3d.com/sugges...he-wheel-collider-to-enable-it-to-roll-freely) But really, this is a bug. Having the requirement of adding motor torque to a wheel in order for it to respect external forces applied to its rigid body has to be considered a bug. Please, please fix this. Having the wheels waking up when external forces are applied to the rigid body has to be a relatively simple check to add...? Thanks in advance!